Tropical cyclone

Tropical cyclone

Overview
A tropical cyclone is a storm system
Storm
A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...

 characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclone
Cyclone
In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...

s strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

 of water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

 contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easter
Nor'easter
A nor'easter is a type of macro-scale storm along the East Coast of the United States and Atlantic Canada, so named because the storm travels to the northeast from the south and the winds come from the northeast, especially in the coastal areas of the Northeastern United States and Atlantic Canada...

s, European windstorm
European windstorm
A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

s, and polar low
Polar low
A polar low is a small-scale, long-lived atmospheric low pressure system that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. The systems usually have a horizontal length scale of less than and exist for no more than a couple of days. ...

s.
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Encyclopedia
A tropical cyclone is a storm system
Storm
A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...

 characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclone
Cyclone
In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...

s strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

 of water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

 contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easter
Nor'easter
A nor'easter is a type of macro-scale storm along the East Coast of the United States and Atlantic Canada, so named because the storm travels to the northeast from the south and the winds come from the northeast, especially in the coastal areas of the Northeastern United States and Atlantic Canada...

s, European windstorm
European windstorm
A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

s, and polar low
Polar low
A polar low is a small-scale, long-lived atmospheric low pressure system that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. The systems usually have a horizontal length scale of less than and exist for no more than a couple of days. ...

s. The characteristic that separates tropical cyclones from other cyclonic systems is that at any height in the atmosphere, the center of a tropical cyclone will be warmer than its surroundings; a phenomenon called "warm core" storm systems.

The term "tropical" refers both to the geographical origin of these systems, which usually form in tropical
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

 regions of the globe, and to their formation in maritime tropical air masses. The term "cyclone" refers to such storms' cyclonic nature, with counterclockwise wind flow in the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

 and clockwise wind flow in the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

. The opposite direction of the wind flow is a result of the Coriolis force. Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane (ˈhʌrɨkeɪn, ˈhʌrɨkən), typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone.

While tropical cyclones can produce extremely powerful winds and torrential rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...

, they are also able to produce high waves and damaging storm surge
Storm surge
A storm surge is an offshore rise of water associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea...

 as well as spawning tornadoes. They develop over large bodies of warm water, and lose their strength if they move over land due to increased surface friction and loss of the warm ocean as an energy source. This is why coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

ing up to 40 kilometres (24.9 mi) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can relieve drought
Drought
A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...

 conditions. They also carry heat energy away from the tropics and transport it toward temperate
Temperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...

 latitudes, which makes them an important part of the global atmospheric circulation
Atmospheric circulation
Atmospheric circulation is the large-scale movement of air, and the means by which thermal energy is distributed on the surface of the Earth....

 mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

, and to maintain a relatively stable and warm temperature worldwide.

Many tropical cyclones develop
Tropical cyclogenesis
Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

 when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. The background environment is modulated by climatological cycles and patterns such as the Madden-Julian oscillation
Madden-Julian oscillation
The Madden–Julian oscillation ' is the largest element of the intraseasonal variability in the tropical atmosphere. It is a large-scale coupling between atmospheric circulation and tropical deep convection...

, El Niño-Southern Oscillation
El Niño-Southern Oscillation
El Niño/La Niña-Southern Oscillation, or ENSO, is a quasiperiodic climate pattern that occurs across the tropical Pacific Ocean roughly every five years...

, and the Atlantic multidecadal oscillation
Atlantic Multidecadal Oscillation
The Atlantic multidecadal oscillation is a mode of variability occurring in the North Atlantic Ocean and which has its principal expression in the sea surface temperature field...

. Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an eye
Eye (cyclone)
The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...

. On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. It is not possible to artificially induce the dissipation of these systems with current technology.

Physical structure


All tropical cyclones are areas of low
Low pressure area
A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...

 atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 in the Earth's atmosphere. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at sea level
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

. Tropical cyclones are characterized and driven by the release of large amounts of latent heat of condensation, which occurs when moist air is carried upwards and its water vapor
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

 condenses. This heat is distributed vertically around the center of the storm. Thus, at any given altitude (except close to the surface, where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.

Eye and center


A strong tropical cyclone will harbor an area of sinking air at the center of circulation. If this area is strong enough, it can develop into a large "eye". Weather in the eye is normally calm and free of clouds, although the sea may be extremely violent. The eye is normally circular in shape, and is typically 30–65 km (20–40 miles) in diameter
Diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

, though eyes as small as 3 kilometres (1.9 mi) and as large as 370 kilometres (229.9 mi) have been observed. Intense, mature tropical cyclones can sometimes exhibit an outward curving of the eyewall's top, making it resemble an arena football stadium; this phenomenon is thus sometimes referred to as the stadium effect. It is usually coldest in the center.

There are other features that either surround the eye, or cover it. The central dense overcast is the concentrated area of strong thunderstorm activity near the center of a tropical cyclone; in weaker tropical cyclones, the CDO may cover the center completely. The eyewall is a circle of strong thunderstorms that surrounds the eye; here is where the greatest wind speeds are found, where clouds reach the highest, and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land. Eyewall replacement cycles occur naturally in intense tropical cyclones. When cyclones reach peak intensity they usually have an eyewall and radius of maximum wind
Radius of maximum wind
The radius of maximum wind is the distance between the center of a cyclone and its band of strongest winds. It is a parameter in atmospheric dynamics and tropical cyclone forecasting. The highest rainfall rates occur near the RMW of tropical cyclones. The extent of a cyclone's storm surge and...

s that contract to a very small size, around 10 kilometres (6.2 mi) to 25 kilometres (15.5 mi). Outer rainbands can organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and angular momentum
Angular momentum
In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...

. When the inner eyewall weakens, the tropical cyclone weakens (in other words, the maximum sustained winds weaken and the central pressure rises.) The outer eyewall replaces the inner one completely at the end of the cycle. The storm can be of the same intensity as it was previously or even stronger after the eyewall replacement cycle finishes. The storm may strengthen again as it builds a new outer ring for the next eyewall replacement.
Size descriptions of tropical cyclones
ROCI Type
Less than 2 degrees latitude Very small/midget
2 to 3 degrees of latitude Small
3 to 6 degrees of latitude Medium/Average
6 to 8 degrees of latitude Large
Over 8 degrees of latitude Very large

Size


One measure of the size of a tropical cyclone is determined by measuring the distance from its center of circulation to its outermost closed isobar, also known as its ROCI
Radius of outermost closed isobar
style="float: right; clear: right; background-color: transparent; margin-left: 0em"|The radius of outermost closed isobar is one of the quantities used to determine the size of a tropical cyclone. It is determined by measuring the radii from the center of the storm to its outermost closed isobar...

. If the radius is less than two degrees of latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

 or 222 kilometres (137.9 mi), then the cyclone is "very small" or a "midget". A radius between 3 and 6 latitude degrees or 333 kilometres (206.9 mi) to 670 kilometres (416.3 mi) are considered "average-sized". "Very large" tropical cyclones have a radius of greater than 8 degrees or 888 kilometres (551.8 mi). Use of this measure has objectively determined that tropical cyclones in the northwest Pacific Ocean are the largest on earth on average, with Atlantic tropical cyclones roughly half their size. Other methods of determining a tropical cyclone's size include measuring the radius of gale force winds and measuring the radius at which its relative vorticity field decreases to 1×10−5 s−1 from its center.

Mechanics


A tropical cyclone's primary energy source is the release of the heat of condensation from water vapor condensing
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

, with solar heating being the initial source for evaporation. Therefore, a tropical cyclone can be visualized as a giant vertical heat engine
Heat engine
In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...

 supported by mechanics driven by physical forces such as the rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

 and gravity of the Earth. In another way, tropical cyclones could be viewed as a special type of mesoscale convective complex
Mesoscale Convective Complex
A mesoscale convective complex is a unique kind of mesoscale convective system which is defined by characteristics observed in infrared satellite imagery. They are long-lived, nocturnal in formation and commonly contain heavy rainfall, wind, hail, lightning and possibly tornadoes.-Size:A...

, which continues to develop over a vast source of relative warmth and moisture. While an initial warm core system, such as an organized thunderstorm complex, is necessary for the formation of a tropical cyclone, a large flux of energy is needed to lower atmospheric pressure
Atmospheric pressure
Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 more than a few millibars (0.10 inch of mercury
Mercury (element)
Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

). The inflow
Inflow (meteorology)
Inflow is the flow of a fluid into a large collection of that fluid. Within meteorology, inflow normally refers to the influx of warmth and moisture from air within the Earth's atmosphere into storm systems. Extratropical cyclones are fed by inflow focused along their cold front and warm fronts...

 of warmth and moisture from the underlying ocean surface is critical for tropical cyclone strengthening. A significant amount of the inflow in the cyclone is in the lowest 1 kilometres (3,280.8 ft) of the atmosphere.

Condensation leads to higher wind speeds, as a tiny fraction of the released energy is converted into mechanical energy; the faster winds and lower pressure associated with them in turn cause increased surface evaporation and thus even more condensation. Much of the released energy drives updrafts
Vertical draft
An updraft or downdraft is the vertical movement of air as a weather related phenomenon. One of two forces causes the air to move. Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding region, and so will rise...

 that increase the height of the storm clouds, speeding up condensation. This positive feedback loop, called the Wind-induced surface heat exchange
Wind-induced surface heat exchange
The wind-induced surface heat exchange is a positive feedback mechanism between the ocean and atmosphere in which a stronger ocean-to-atmosphere heat flux results in a stronger atmospheric circulation, which results in a strong heat flux. It has been hypothesized that this is the mechanism that...

, continues for as long as conditions are favorable for tropical cyclone development
Tropical cyclogenesis
Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

. Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. The rotation of the Earth causes the system to spin, an effect known as the Coriolis effect
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

, giving it a cyclonic characteristic and affecting the trajectory of the storm. In the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

, where the cyclone's wind flow is counterclockwise, the fastest winds relative to the surface of the Earth occur on the eastern side of a northward-moving storm and on the northern side of a westward-moving one; the opposite occurs in the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

, where the wind flow is clockwise
Clockwise
Circular motion can occur in two possible directions. A clockwise motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back to the top...

.

What primarily distinguishes tropical cyclones from other meteorological phenomena is deep convection
Deep convection
Deep convection is a convective process in a medium, usually in an atmosphere or ocean, that in some sense spans the vertical.Within the atmosphere, this means from the surface to above the 500 hPa level, generally stopping at or defining the tropopause at around 200 hPa...

 as a driving force. Because convection is strongest in a tropical climate
Tropical climate
A tropical climate is a climate of the tropics. In the Köppen climate classification it is a non-arid climate in which all twelve months have mean temperatures above...

, it defines the initial domain of the tropical cyclone. By contrast, mid-latitude cyclone
Mid-latitude cyclone
Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere . Cyclogenesis is an umbrella term for several different processes, all of which result in the development of some sort of cyclone. It can occur at various scales, from the microscale to the synoptic scale...

s draw their energy mostly from pre-existing horizontal temperature gradient
Gradient
In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....

s in the atmosphere. To continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the needed atmospheric moisture to keep the positive feedback loop running. When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly.


The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, which can influence subsequent cyclone development. This cooling is primarily caused by wind-driven mixing of cold water from deeper in the ocean and the warm surface waters. This effect results in a negative feedback process that can inhibit further development or lead to weakening. Additional cooling may come in the form of cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days.

Scientists estimate that a tropical cyclone releases heat energy at the rate of 50 to 200 exajoules (1018 J) per day, equivalent to about 1 PW (1015 watt). This rate of energy release is equivalent to 70 times the world energy consumption
World energy resources and consumption
]World energy consumption in 2010: over 5% growthEnergy markets have combined crisis recovery and strong industry dynamism. Energy consumption in the G20 soared by more than 5% in 2010, after the slight decrease of 2009. This strong increase is the result of two converging trends...

 of humans and 200 times the worldwide electrical generating capacity, or to exploding a 10-megaton
TNT equivalent
TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

 nuclear bomb every 20 minutes.

In the lower troposphere, the most obvious motion of clouds is toward the center. However tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine. This outflow produces high, cirrus cloud
Cirrus cloud
Cirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...

s that spiral away from the center. The clouds thin as they move outwards from the center of the system and are evaporated. They may be thin enough for the sun to be visible through them. These high cirrus clouds may be the first signs of an approaching tropical cyclone. As air parcels are lifted within the eye of the storm the vorticity is reduced, causing the outflow from a tropical cyclone to have anti-cyclonic motion.

Major basins and related warning centers


Basins and WMO
World Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

 Monitoring Institutions
Basin Responsible RSMCs and TCWCs
North Atlantic National Hurricane Center
National Hurricane Center
The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...

 (United States)
North-East Pacific National Hurricane Center
National Hurricane Center
The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...

 (United States)
North-Central Pacific Central Pacific Hurricane Center
Central Pacific Hurricane Center
The Central Pacific Hurricane Center of the United States National Weather Service is the official body responsible for tracking and issuing tropical cyclone warnings, watches, advisories, discussions, and statements for the Central North Pacific Basin...

 (United States)
North-West Pacific Japan Meteorological Agency
Japan Meteorological Agency
The or JMA, is the Japanese government's weather service. Charged with gathering and reporting weather data and forecasts in Japan, it is a semi-autonomous part of the Ministry of Land, Infrastructure and Transport...

North Indian Ocean India Meteorological Department
India Meteorological Department
The India Meteorological Department , also referred to as the Met Office, is an agency of the Ministry of Earth Sciences of the Government of India. It is the principal agency responsible for meteorological observations, weather forecasting and seismology...

South-West Indian Ocean Météo-France
Météo-France
Météo-France is the French national meteorological service.The organisation was established by decree in June 1993 and is a department of the Ministry of Transportation. It is headquartered in Paris but many domestic operations have been decentralised to Toulouse...

Australian region Bureau of Meteorology
Bureau of Meteorology
The Bureau of Meteorology is an Executive Agency of the Australian Government responsible for providing weather services to Australia and surrounding areas. It was established in 1906 under the Meteorology Act, and brought together the state meteorological services that existed before then...

(Australia)
Meteorological and Geophysical Agency (Indonesia)
Papua New Guinea National Weather Service
Southern Pacific Fiji Meteorological Service
Fiji Meteorological Service
The Fiji Meteorological Service is a Department of the government of Fiji responsible for providing weather forecasts and is based in Nadi. Since 1995, FMS has been responsible for naming and tracking tropical cyclones in the Southwest Pacific region...


Meteorological Service of New Zealand
: Indicates a Tropical Cyclone Warning Center


There are six Regional Specialized Meteorological Center
Regional Specialized Meteorological Center
A Regional Specialized Meteorological Centre is responsible for the distribution of information, advisories, and warnings regarding the specific program they have a part of, agreed by consensus at the World Meteorological Organization as part of the World Weather Watch.-Tropical...

s (RSMCs) worldwide. These organizations are designated by the World Meteorological Organization
World Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

 and are responsible for tracking and issuing bulletins, warnings, and advisories about tropical cyclones in their designated areas of responsibility. In addition, there are six Tropical Cyclone Warning Centers (TCWCs) that provide information to smaller regions. The RSMCs and TCWCs are not the only organizations that provide information about tropical cyclones to the public. The Joint Typhoon Warning Center
Joint Typhoon Warning Center
The Joint Typhoon Warning Center is a joint United States Navy – United States Air Force task force located at the Naval Maritime Forecast Center in Pearl Harbor, Hawaii...

 (JTWC) issues advisories in all basins except the Northern Atlantic for the purposes of the United States Government. The Philippine Atmospheric, Geophysical and Astronomical Services Administration
Philippine Atmospheric, Geophysical and Astronomical Services Administration
The Philippine Atmospheric, Geophysical and Astronomical Services Administration is a Philippine national institution dedicated to provide flood and typhoon warnings, public weather forecasts and advisories, meteorological, astronomical, climatological, and other specialized information and...

 (PAGASA) issues advisories and names for tropical cyclones that approach the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

 in the Northwestern Pacific to protect the life and property of its citizens. The Canadian Hurricane Center (CHC) issues advisories on hurricanes and their remnants for Canadian citizens when they affect Canada.

On 26 March 2004, Cyclone Catarina
Cyclone Catarina
Cyclone Catarina is one of several informal names for a South Atlantic tropical cyclone that hit southeastern Brazil in late March 2004. The storm developed out of a stationary cold-core upper-level trough on March 12...

 became the first recorded South Atlantic cyclone
South Atlantic tropical cyclone
South Atlantic tropical cyclones are unusual weather events that occur in the southern hemisphere. Strong wind shear and a lack of weather disturbances favorable for tropical cyclone development make any hurricane-strength cyclones extremely rare...

 and subsequently struck southern Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

 with winds equivalent to Category 2 on the Saffir-Simpson Hurricane Scale
Saffir-Simpson Hurricane Scale
The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...

. As the cyclone formed outside the authority of another warning center, Brazilian meteorologists initially treated the system as an extratropical cyclone
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

, although subsequently classified it as tropical.

Formation





Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active while November is the only month with all the tropical cyclone basins active.

Times


In the Northern Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, a distinct cyclone season
Atlantic hurricane season
The Atlantic hurricane season is the period in a year when hurricanes usually form in the Atlantic Ocean. Tropical cyclones in the North Atlantic are called hurricanes, tropical storms, or tropical depressions. In addition, there have been several storms over the years that have not been fully...

 occurs from June 1 to November 30, sharply peaking from late August through September. The statistical peak of the Atlantic hurricane season is 10 September. The Northeast Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November. In the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

, the tropical cyclone year begins on July 1 and runs all year-round and encompasses the tropical cyclone seasons, which run from November 1 until the end of April, with peaks in mid-February to early March.

Season lengths and seasonal averages
Basin Season start Season end Tropical Storms
(>34 knots)
Tropical Cyclones
(>63 knots)
Category 3+ TCs
(>95 knots)
Northwest Pacific April January 26.7 16.9 8.5
South Indian November April 20.6 10.3 4.3
Northeast Pacific May November 16.3 9.0 4.1
North Atlantic June November 10.6 5.9 2.0
Australia Southwest Pacific November April 9 4.8 1.9
North Indian April December 5.4 2.2 0.4


Factors


The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood. While six factors appear to be generally necessary, tropical cyclones may occasionally form without meeting all of the following conditions. In most situations, water temperatures
Sea surface temperature
Sea surface temperature is the water temperature close to the oceans surface. The exact meaning of surface varies according to the measurement method used, but it is between and below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a...

 of at least 26.5 °C (79.7 °F) are needed down to a depth of at least 50 m (164 ft); waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms. Another factor is rapid cooling with height, which allows the release of the heat of condensation that powers a tropical cyclone. High humidity is needed, especially in the lower-to-mid troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

; when there is a great deal of moisture in the atmosphere, conditions are more favorable for disturbances to develop. Low amounts of wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...

 are needed, as high shear is disruptive to the storm's circulation. Tropical cyclones generally need to form more than 555 km (344.9 mi) or 5 degrees of latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

 away from the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

, allowing the Coriolis effect
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

 to deflect winds blowing towards the low pressure center and creating a circulation. Lastly, a formative tropical cyclone needs a pre-existing system of disturbed weather, although without a circulation no cyclonic development will take place. Low-latitude and low-level westerly wind bursts associated with the Madden-Julian oscillation
Madden-Julian oscillation
The Madden–Julian oscillation ' is the largest element of the intraseasonal variability in the tropical atmosphere. It is a large-scale coupling between atmospheric circulation and tropical deep convection...

 can create favorable conditions for tropical cyclogenesis by initiating tropical disturbances.

Locations


Most tropical cyclones form in a worldwide band of thunderstorm activity called by several names: the Intertropical Front (ITF), the Intertropical Convergence Zone
Intertropical Convergence Zone
The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....

 (ITCZ), or the monsoon trough
Monsoon trough
The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...

. Another important source of atmospheric instability is found in tropical wave
Tropical wave
Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which move from east to west across the tropics causing areas of...

s, which cause about 85% of intense tropical cyclones in the Atlantic ocean, and become most of the tropical cyclones in the Eastern Pacific basin.

Tropical cyclones move westward when equatorward of the subtropical ridge
Subtropical ridge
The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

, intensifying as they move. Most of these systems form between 10 and 30 degrees away of the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

, and 87% form no farther away than 20 degrees of latitude, north or south. Because the Coriolis effect
Coriolis effect
In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

 initiates and maintains tropical cyclone rotation, tropical cyclones rarely form or move within about 5 degrees of the equator, where the Coriolis effect is weakest. However, it is possible for tropical cyclones to form within this boundary as Tropical Storm Vamei
Tropical Storm Vamei
Tropical Storm Vamei was a Pacific tropical cyclone that formed closer to the equator than any other tropical cyclone worldwide...

 did in 2001 and Cyclone Agni
Cyclone Agni
Severe Cyclonic Storm Agni was a tropical cyclone of the 2004 North Indian Ocean cyclone season notable for its record proximity to the equator. It was the second North Indian Ocean cyclone to receive a name, after Onil earlier in the year...

 in 2004.

Steering winds



Although tropical cyclones are large systems generating enormous energy, their movements over the Earth's surface are controlled by large-scale winds—the streams in the Earth's atmosphere. The path of motion is referred to as a tropical cyclone's track and has been compared by Dr. Neil Frank, former director of the National Hurricane Center
National Hurricane Center
The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...

, to "leaves carried along by a stream".

Tropical systems, while generally located equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

ward of the 20th parallel, are steered primarily westward by the east-to-west winds on the equatorward side of the subtropical ridge
Subtropical ridge
The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

—a persistent high-pressure area over the world's oceans. In the tropical North Atlantic and Northeast Pacific oceans, trade winds—another name for the westward-moving wind currents—steer tropical waves westward from the African coast and towards the Caribbean Sea, North America, and ultimately into the central Pacific ocean before the waves dampen out. These waves are the precursors to many tropical cyclones within this region. In the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

 and Western Pacific (both north and south of the equator), tropical cyclogenesis is strongly influenced by the seasonal movement of the Intertropical Convergence Zone
Intertropical Convergence Zone
The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....

 and the monsoon trough
Monsoon trough
The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...

, rather than by easterly waves. Tropical cyclones can also be steered by other systems, such as other low pressure systems, high pressure systems, warm front
Warm front
A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient...

s, and cold front
Cold front
A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...

s.

Coriolis effect



The Earth's rotation imparts an acceleration known as the Coriolis effect, Coriolis acceleration, or colloquially, Coriolis force. This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents. The poleward portion of a tropical cyclone contains easterly winds, and the Coriolis effect pulls them slightly more poleward. The westerly winds on the equatorward portion of the cyclone pull slightly towards the equator, but, because the Coriolis effect weakens toward the equator, the net drag on the cyclone is poleward. Thus, tropical cyclones in the Northern Hemisphere usually turn north (before being blown east), and tropical cyclones in the Southern Hemisphere usually turn south (before being blown east) when no other effects counteract the Coriolis effect.

The Coriolis effect also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds – that force is the heat of condensation.

Interaction with the mid-latitude westerlies




When a tropical cyclone crosses the subtropical ridge
Subtropical ridge
The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

 axis, its general track around the high-pressure area is deflected significantly by winds moving towards the general low-pressure area to its north. When the cyclone track becomes strongly poleward with an easterly component, the cyclone has begun recurvature. A typhoon moving through the Pacific Ocean towards Asia, for example, will recurve offshore of Japan to the north, and then to the northeast, if the typhoon encounters southwesterly winds (blowing northeastward) around a low-pressure system passing over China or Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...

. Many tropical cyclones are eventually forced toward the northeast by extratropical cyclone
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

s in this manner, which move from west to east to the north of the subtropical ridge. An example of a tropical cyclone in recurvature was Typhoon Ioke
Hurricane Ioke
Hurricane Ioke was the strongest hurricane ever recorded in the Central Pacific...

 in 2006, which took a similar trajectory.

Landfall



Officially, landfall
Landfall (meteorology)
Landfall is the event of a tropical cyclone or a waterspout coming onto land after being over water. When a waterspout makes landfall it is reclassified as a tornado, which can then cause damage inland...

is when a storm's center (the center of its circulation, not its edge) crosses the coastline. Storm conditions may be experienced on the coast and inland hours before landfall; in fact, a tropical cyclone can launch its strongest winds over land, yet not make landfall; if this occurs, then it is said that the storm made a direct hit on the coast. As a result of the narrowness of this definition, the landfall area experiences half of a land-bound storm by the time the actual landfall occurs. For emergency preparedness, actions should be timed from when a certain wind speed or intensity of rainfall will reach land, not from when landfall will occur.

Multiple storm interaction



When two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. This phenomenon is called the Fujiwhara effect, after Sakuhei Fujiwhara
Sakuhei Fujiwhara
was a Japanese meteorologist who became the namesake for the Fujiwhara effect. Novelist Jirō Nitta is his nephew and mathematician Masahiko Fujiwara is his grandnephew.-Early life:...

.

Factors



A tropical cyclone can cease to have tropical characteristics in several different ways. One such way is if it moves over land, thus depriving it of the warm water it needs to power itself, quickly losing strength. Most strong storms lose their strength very rapidly after landfall and become disorganized areas of low pressure within a day or two, or evolve into extratropical cyclone
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

s. There is a chance a tropical cyclone could regenerate if it managed to get back over open warm water, such as with Hurricane Ivan
Hurricane Ivan
Hurricane Ivan was a large, long-lived, Cape Verde-type hurricane that caused widespread damage in the Caribbean and United States. The cyclone was the ninth named storm, the sixth hurricane and the fourth major hurricane of the active 2004 Atlantic hurricane season...

. If it remains over mountains for even a short time, weakening will accelerate. Many storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall, leading to deadly flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

s and mudslides, similar to those that happened with Hurricane Mitch
Hurricane Mitch
Hurricane Mitch was the most powerful hurricane and the most destructive of the 1998 Atlantic hurricane season, with maximum sustained winds of 180 mph . The storm was the thirteenth tropical storm, ninth hurricane, and third major hurricane of the season. Along with Hurricane Georges, Mitch...

 in 1998. In addition, dissipation can occur if a storm remains in the same area of ocean for too long, mixing the upper 60 metres (196.9 ft) of water, dropping sea surface temperatures more than 5 °C (9 °F). Without warm surface water, the storm cannot survive.

A tropical cyclone can dissipate when it moves over waters significantly below 26.5 °C (79.7 °F). This will cause the storm to lose its tropical characteristics (i.e. thunderstorms near the center and warm core) and become a remnant low pressure area, which can persist for several days. This is the main dissipation mechanism in the Northeast Pacific ocean. Weakening or dissipation can occur if it experiences vertical wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...

, causing the convection and heat engine to move away from the center; this normally ceases development of a tropical cyclone. In addition, its interaction with the main belt of the Westerlies, by means of merging with a nearby frontal zone, can cause tropical cyclones to evolve into extratropical cyclones. This transition can take 1–3 days. Even after a tropical cyclone is said to be extratropical or dissipated, it can still have tropical storm force (or occasionally hurricane/typhoon force) winds and drop several inches of rainfall. In the Pacific ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

 and Atlantic ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, such tropical-derived cyclones of higher latitudes can be violent and may occasionally remain at hurricane or typhoon-force wind speeds when they reach the west coast of North America. These phenomena can also affect Europe, where they are known as European windstorm
European windstorm
A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

s
; Hurricane Iris's
Hurricane Iris (1995)
Hurricane Iris was the ninth named tropical cyclone and fifth hurricane of an active 1995 Atlantic hurricane season. Iris was one of four storms to form nearly simultaneously in the Atlantic during the 1995 season. Forming on August 22, Iris slowly drifted across the Leeward Islands as a tropical...

 extratropical remnants are an example of such a windstorm from 1995. In addition, a cyclone can merge with another area of low pressure, becoming a larger area of low pressure. This can strengthen the resultant system, although it may no longer be a tropical cyclone. Studies in the 2000s have given rise to the hypothesis that large amounts of dust reduce the strength of tropical cyclones.

Artificial dissipation


In the 1960s and 1970s, the United States government attempted to weaken hurricanes through Project Stormfury
Project Stormfury
Project Stormfury was an attempt to weaken tropical cyclones by flying aircraft into them and seeding with silver iodide. The project was run by the United States Government from 1962 to 1983....

 by seeding
Cloud seeding
Cloud seeding, a form of intentional weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud...

 selected storms with silver iodide
Silver iodide
Silver iodide is a yellow, inorganic, photosensitive iodide of silver used in photography, in medicine as an antiseptic, and in rainmaking for cloud seeding.-Crystal structure:...

. It was thought that the seeding would cause supercooled water in the outer rainbands to freeze, causing the inner eyewall to collapse and thus reducing the winds. The winds of Hurricane Debbie
Hurricane Debbie (1969)
Hurricane Debbie was an intense and long-lived hurricane that formed during August 1969. The fifth tropical cyclone, fourth named storm, third hurricane and second major hurricane of the 1969 Atlantic hurricane season, Debbie formed on August 14 in the southern Atlantic Ocean and took a general...

—a hurricane seeded in Project Stormfury—dropped as much as 31%, but Debbie regained its strength after each of two seeding forays. In an earlier episode in 1947, disaster struck when a hurricane east of Jacksonville, Florida
Jacksonville, Florida
Jacksonville is the largest city in the U.S. state of Florida in terms of both population and land area, and the largest city by area in the contiguous United States. It is the county seat of Duval County, with which the city government consolidated in 1968...

 promptly changed its course after being seeded, and smashed into Savannah, Georgia
Savannah, Georgia
Savannah is the largest city and the county seat of Chatham County, in the U.S. state of Georgia. Established in 1733, the city of Savannah was the colonial capital of the Province of Georgia and later the first state capital of Georgia. Today Savannah is an industrial center and an important...

. Because there was so much uncertainty about the behavior of these storms, the federal government would not approve seeding operations unless the hurricane had a less than 10% chance of making landfall within 48 hours, greatly reducing the number of possible test storms. The project was dropped after it was discovered that eyewall replacement cycles occur naturally in strong hurricanes, casting doubt on the result of the earlier attempts. Today, it is known that silver iodide seeding is not likely to have an effect because the amount of supercooled water in the rainbands of a tropical cyclone is too low.

Other approaches have been suggested over time, including cooling the water under a tropical cyclone by towing iceberg
Iceberg
An iceberg is a large piece of ice from freshwater that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice...

s into the tropical oceans. Other ideas range from covering the ocean in a substance that inhibits evaporation, dropping large quantities of ice into the eye at very early stages of development (so that the latent heat is absorbed by the ice, instead of being converted to kinetic energy that would feed the positive feedback loop), or blasting the cyclone apart with nuclear weapons. Project Cirrus even involved throwing dry ice on a cyclone. These approaches all suffer from one flaw above many others: tropical cyclones are simply too large and short-lived for any of the weakening techniques to be practical.

Effects




Tropical cyclones out at sea cause large waves, heavy rain, and high winds, disrupting international shipping and, at times, causing shipwrecks. Tropical cyclones stir up water, leaving a cool wake behind them, which causes the region to be less favorable for subsequent tropical cyclones. On land, strong wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...

s can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. The storm surge
Storm surge
A storm surge is an offshore rise of water associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea...

, or the increase in sea level due to the cyclone, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths.
The broad rotation of a landfalling tropical cyclone, and vertical wind shear at its periphery, spawns tornadoes
History of tropical cyclone-spawned tornadoes
Intense tropical cyclones usually produce tornadoes, the majority of them weak, especially upon landfall.- List of Atlantic tropical cyclones which spawned tornadoes :These are the Atlantic tropical cyclones that are known to have spawned tornadoes in the U.S....

. Tornadoes can also be spawned as a result of eyewall mesovortices, which persist until landfall.

Over the past two centuries, tropical cyclones have been responsible for the deaths of about 1.9 million people worldwide. Large areas of standing water caused by flooding lead to infection, as well as contributing to mosquito-borne illnesses. Crowded evacuees in shelters
Emergency shelter
Emergency shelters are places for people to live temporarily when they can't live in their previous residence, similar to homeless shelters. The main difference is that an emergency shelter typically specializes in people fleeing a specific type of situation, such as natural or man-made disasters,...

 increase the risk of disease propagation. Tropical cyclones significantly interrupt infrastructure, leading to power outages, bridge destruction, and the hampering of reconstruction efforts.

Although cyclones take an enormous toll in lives and personal property, they may be important factors in the precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...

 regimes of places they impact, as they may bring much-needed precipitation to otherwise dry regions. Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes
Middle latitudes
The middle latitudes are between 23°26'22" North and 66°33'39" North, and between 23°26'22" South and 66°33'39" South latitude, or, the Earth's temperate zones between the tropics and the Arctic and Antarctic. The prevailing winds in the middle latitudes are often very strong...

 and polar regions, and by regulating the thermohaline circulation
Thermohaline circulation
The term thermohaline circulation refers to a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....

 through upwelling
Upwelling
Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...

. The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

, which are typically important fish breeding locales. Tropical cyclone destruction spurs redevelopment, greatly increasing local property values.

Observation




Intense tropical cyclones pose a particular observation challenge, as they are a dangerous oceanic phenomenon, and weather station
Weather station
A weather station is a facility, either on land or sea, with instruments and equipment for observing atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include temperature, barometric pressure, humidity, wind speed, wind...

s, being relatively sparse, are rarely available on the site of the storm itself. In general, surface observations are available only if the storm is passing over an island or a coastal area, or if there is a nearby ship. Real-time measurements are usually taken in the periphery of the cyclone, where conditions are less catastrophic and its true strength cannot be evaluated. For this reason, there are teams of meteorologists that move into the path of tropical cyclones to help evaluate their strength at the point of landfall.

Tropical cyclones far from land are tracked by weather satellite
Weather satellite
The weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while...

s capturing visible and infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

 images from space, usually at half-hour to quarter-hour intervals. As a storm approaches land, it can be observed by land-based Doppler
Pulse-doppler radar
Pulse-Doppler is a 4D radar system capable of detecting both target 3D location as well as measuring radial velocity . It uses the Doppler effect to avoid overloading computers and operators as well as to reduce power consumption...

 radar
Weather radar
Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...

. Radar plays a crucial role around landfall by showing a storm's location and intensity every several minutes.

In situ
In situ
In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may...

 measurements, in real-time, can be taken by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by United States government hurricane hunters
Hurricane Hunters
The Hurricane Hunters are aircraft that fly into tropical cyclones in the North Atlantic Ocean and Northeastern Pacific Ocean for the specific purpose of directly measuring weather data in and around those storms. In the United States, the Air Force, Navy, and NOAA units have all participated in...

. The aircraft used are WC-130 Hercules and WP-3D Orions, both four-engine turboprop
Turboprop
A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...

 cargo aircraft. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft also launch GPS dropsondes inside the cyclone. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface. A new era in hurricane observation began when a remotely piloted Aerosonde
Insitu Aerosonde
The Aerosonde is a small unmanned aerial vehicle designed to collect weather data, including temperature, atmospheric pressure, humidity, and wind measurements, over oceans and remote areas. The Aerosonde was developed by Insitu, and is now manufactured by Aerosonde Ltd, which is a strategic...

, a small drone aircraft, was flown through Tropical Storm Ophelia as it passed Virginia's Eastern Shore during the 2005 hurricane season. A similar mission was also completed successfully in the western Pacific ocean. This demonstrated a new way to probe the storms at low altitudes that human pilots seldom dare.


Forecasting



Because of the forces that affect tropical cyclone tracks, accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will change during the life of a tropical system. The deep layer mean flow, or average wind through the depth of the troposphere
Troposphere
The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

, is considered the best tool in determining track direction and speed. If storms are significantly sheared, use of wind speed measurements at a lower altitude, such as at the 700 hPa pressure surface (3000 metres (9,842.5 ft) above sea level) will produce better predictions. Tropical forecasters also consider smoothing out short-term wobbles of the storm as it allows them to determine a more accurate long-term trajectory. High-speed computers and sophisticated simulation software allow forecasters to produce computer models
Tropical cyclone prediction model
A tropical cyclone forecast model is a computer program that uses meteorological data to forecast aspects of the future state of tropical cyclones. There are three types of models: statistical, dynamical, or combined statistical-dynamic...

 that predict tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. Combining forecast models with increased understanding of the forces that act on tropical cyclones, as well as with a wealth of data from Earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades. However, scientists are not as skillful at predicting the intensity of tropical cyclones. The lack of improvement in intensity forecasting is attributed to the complexity of tropical systems and an incomplete understanding of factors that affect their development.

Intensity classifications




Tropical cyclones are classified into three main groups, based on intensity: tropical depressions, tropical storms, and a third group of more intense storms, whose name depends on the region. For example, if a tropical storm in the Northwestern Pacific reaches hurricane-strength winds on the Beaufort scale
Beaufort scale
The Beaufort Scale is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the Beaufort Wind Force Scale.-History:...

, it is referred to as a typhoon; if a tropical storm passes the same benchmark in the Northeast Pacific Basin
Pacific hurricane
A Pacific hurricane or tropical storm is a tropical cyclone that develops in the northeastern part of the Pacific Ocean. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, , central , and western...

, or in the Atlantic
Atlantic hurricane
North Atlantic tropical cyclones usually form in the northern hemisphere summer or fall. Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph , while hurricanes have one-minute maximum sustained exceeding 74 mph...

, it is called a hurricane. Neither "hurricane" nor "typhoon" is used in either the Southern Hemisphere or the Indian Ocean. In these basins
Tropical cyclone basins
Traditionally, areas of tropical cyclone formation are divided into seven basins. These include the north Atlantic Ocean, the eastern and western parts of the northern Pacific Ocean, the southwestern Pacific, the southwestern and southeastern Indian Oceans, and the northern Indian Ocean. The...

, storms of tropical nature are referred to simply as "cyclones".

As indicated in the table below, each basin uses a separate system of terminology
Tropical cyclone scales
Tropical systems are officially ranked on one of several tropical cyclone scales according to their maximum sustained winds and in what oceanic basin they are located...

, making comparisons between different basins difficult. In the Pacific Ocean, hurricanes from the Central North Pacific sometimes cross the International Date Line
International Date Line
The International Date Line is a generally north-south imaginary line on the surface of the Earth, passing through the middle of the Pacific Ocean, that designates the place where each calendar day begins...

 into the Northwest Pacific, becoming typhoons (such as Hurricane/Typhoon Ioke
Hurricane Ioke
Hurricane Ioke was the strongest hurricane ever recorded in the Central Pacific...

 in 2006); on rare occasions, the reverse will occur. It should also be noted that typhoons with sustained winds greater than 67 metres per second (123.1 kn) or 150 miles per hour (241.4 km/h) are called Super Typhoons by the Joint Typhoon Warning Center.

Tropical depression


A tropical depression is an organized system of clouds and thunderstorms with a defined, closed surface circulation and maximum sustained wind
Maximum sustained wind
The maximum sustained winds associated with a tropical cyclone are a common indicator of the intensity of the storm. Within a mature tropical cyclone, they are found within the eyewall at a distance defined as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are...

s of less than 17 metres per second (31.2 kn) or 38 miles per hour (61.2 km/h). It has no eye
Eye (cyclone)
The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...

 and does not typically have the organization or the spiral shape of more powerful storms. However, it is already a low-pressure system, hence the name "depression". The practice of the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

 is to name tropical depressions from their own naming convention when the depressions are within the Philippines' area of responsibility.

Tropical storm


A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 17 metres per second (31.2 kn) (39 miles per hour (62.8 km/h)) and 32 metres per second (58.8 kn) (73 miles per hour (117.5 km/h)). At this point, the distinctive cyclonic shape starts to develop, although an eye is not usually present. Government weather services, other than the Philippines, first assign names to systems that reach this intensity (thus the term named storm).

Hurricane or typhoon


A hurricane or typhoon (sometimes simply referred to as a tropical cyclone, as opposed to a depression or storm) is a system with sustained winds of at least 33 metres per second (60.6 kn) or 74 miles per hour (119.1 km/h). A cyclone of this intensity tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of circulation. The eye is often visible in satellite images as a small, circular, cloud-free spot. Surrounding the eye is the eyewall, an area about 16 kilometres (9.9 mi) to 80 kilometres (49.7 mi) wide in which the strongest thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...

s and winds circulate around the storm's center. Maximum sustained winds in the strongest tropical cyclones have been estimated at about 85 metres per second (156.1 kn) or 195 miles per hour (313.8 km/h).

Origin of storm terms


The word typhoon, which is used today in the Northwest Pacific, may be derived from Hindi/Urdu, Persian
Persian language
Persian is an Iranian language within the Indo-Iranian branch of the Indo-European languages. It is primarily spoken in Iran, Afghanistan, Tajikistan and countries which historically came under Persian influence...

 and Arabic
Arabic language
Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

 ţūfān (طوفان), which in turn originates from Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 Typhon
Typhon
Typhon , also Typhoeus , Typhaon or Typhos was the last son of Gaia, fathered by Tartarus, and the most deadly monster of Greek mythology. He was known as the "Father of all monsters"; his wife Echidna was likewise the "Mother of All Monsters."Typhon was described in pseudo-Apollodorus,...

(Τυφών), a monster from Greek mythology
Greek mythology
Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

 associated with storms. The related Portuguese
Portuguese language
Portuguese is a Romance language that arose in the medieval Kingdom of Galicia, nowadays Galicia and Northern Portugal. The southern part of the Kingdom of Galicia became independent as the County of Portugal in 1095...

 word tufão, used in Portuguese for typhoons, is also derived from Typhon. The word is also similar to Chinese "taifeng" ("toifung" in Cantonese
Cantonese
Cantonese is a dialect spoken primarily in south China.Cantonese may also refer to:* Yue Chinese, the Chinese language that includes Cantonese* Cantonese cuisine, the cuisine of Guangdong province...

) (颱風 – great winds), and also to the Japanese "taifu" (台風), which may explain why "typhoon" came to be used for East Asian cyclones.

The word hurricane, used in the North Atlantic and Northeast Pacific, is derived from huracán, the Spanish word for the Carib/Taino
Taíno people
The Taínos were pre-Columbian inhabitants of the Bahamas, Greater Antilles, and the northern Lesser Antilles. It is thought that the seafaring Taínos are relatives of the Arawak people of South America...

 storm god, Juracán
Juracán
Juracán is the phonetic name given by the Spanish settlers to the god of chaos and disorder that the Taino Indians in Puerto Rico believed controlled the weather, particularly hurricanes. From this we derive the Spanish word huracán and eventually the English word hurricane...

. This god is believed by scholars to have been at least partially derived from the Mayan
Maya peoples
The Maya people constitute a diverse range of the Native American people of southern Mexico and northern Central America. The overarching term "Maya" is a collective designation to include the peoples of the region who share some degree of cultural and linguistic heritage; however, the term...

 creator god, Huracan
Huracan
Huracan , in Mayan understandable as Jun Raqan "one legged", is a K'iche' Mayan god of wind, storm, fire and one of the creator deities who participated in all three attempts at creating humanity...

. Huracan was believed by the Mayans to have created dry land out of the turbulent waters. The god was also credited with later destroying the "wooden people", the precursors to the "maize people
Maya maize god
Like other Mesoamerican peoples, the traditional Mayas recognize in their staple crop, the maize, a vital force with which they strongly identify. This is clearly shown by their mythological traditions. According to the 16th-century Popol Vuh, the Hero Twins have maize plants for alter egos and man...

", with an immense storm and flood. Huracan is also the source of the word orcan, another word for a particularly strong European windstorm
European windstorm
A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

.

Naming



Storms reaching tropical storm strength were initially given names to eliminate confusion when there are multiple systems in any individual basin at the same time, which assists in warning people of the coming storm. In most cases, a tropical cyclone retains its name throughout its life; however, under special circumstances, tropical cyclones may be renamed while active. These names are taken from lists that vary from region to region and are usually drafted a few years ahead of time. The lists are decided on, depending on the regions, either by committees of the World Meteorological Organization
World Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

 (called primarily to discuss many other issues) or by national weather offices involved in the forecasting of the storms. Each year, the names of particularly destructive storms (if there are any) are "retired" and new names are chosen to take their place. Different countries have different local conventions; for example, in Japan, storms are referred to by number (each year), such as 台風第9号 (Typhoon #9).

Notable tropical cyclones



Tropical cyclones that cause extreme destruction are rare, although when they occur, they can cause great amounts of damage or thousands of fatalities.
The 1970 Bhola cyclone
1970 Bhola cyclone
The 1970 Bhola cyclone was a devastating tropical cyclone that struck East Pakistan and India's West Bengal on November 12, 1970. It was the deadliest tropical cyclone ever recorded, and one of the deadliest natural disasters in modern times...

 is the deadliest tropical cyclone on record, killing more than 300,000 people and potentially as many as 1 million after striking the densely populated Ganges Delta
Ganges Delta
The Ganges Delta is a river delta in the South Asia region of Bengal, consisting of Bangladesh and the state of West Bengal, India. It is the world's largest delta, and empties into the Bay of Bengal...

 region of Bangladesh
Bangladesh
Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...

 on 13 November 1970. Its powerful storm surge was responsible for the high death toll. The North Indian cyclone basin has historically been the deadliest basin. Elsewhere, Typhoon Nina
Typhoon Nina (1975)
Super Typhoon Nina was a short-lived but intense super typhoon that caused catastrophic damage and loss of life in China after causing the Banqiao Dam to collapse...

 killed nearly 100,000 in China in 1975 due to a 100-year flood
100-year flood
A one-hundred-year flood is calculated to be the level of flood water expected to be equaled or exceeded every 100 years on average. The 100-year flood is more accurately referred to as the 1% annual exceedance probability flood, since it is a flood that has a 1% chance of being equaled or exceeded...

 that caused 62 dams including the Banqiao Dam
Banqiao Dam
The Banqiao Reservoir Dam is a dam on the River Ru in Zhumadian Prefecture, Henan province, China. It infamously failed in 1975, causing more casualties than any other dam failure in history, and was subsequently rebuilt....

 to fail. The Great Hurricane of 1780
Great Hurricane of 1780
The Great Hurricane of 1780, also known as Hurricane San Calixto, the Great Hurricane of the Antilles, and the 1780 Disaster, is the deadliest Atlantic hurricane on record. Over 20,000 people died when the storm passed through the Lesser Antilles in the Caribbean between October 10 and October...

 is the deadliest Atlantic hurricane
Atlantic hurricane
North Atlantic tropical cyclones usually form in the northern hemisphere summer or fall. Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph , while hurricanes have one-minute maximum sustained exceeding 74 mph...

 on record, killing about 22,000 people in the Lesser Antilles
Lesser Antilles
The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...

. A tropical cyclone does need not be particularly strong to cause memorable damage, primarily if the deaths are from rainfall or mudslides. Tropical Storm Thelma
Tropical Storm Thelma
Tropical Storm Thelma was the deadliest tropical storm of the 1991 Pacific typhoon season, killing between 5,101 to 8,100 people as it crossed the Philippines.-Meteorological history:A tropical disturbance developed over the eastern Caroline Islands in late October...

 in November 1991 killed thousands in the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

, while in 1982, the unnamed tropical depression that eventually became Hurricane Paul killed around 1,000 people in Central America
Central America
Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

.

Hurricane Katrina
Hurricane Katrina
Hurricane Katrina of the 2005 Atlantic hurricane season was a powerful Atlantic hurricane. It is the costliest natural disaster, as well as one of the five deadliest hurricanes, in the history of the United States. Among recorded Atlantic hurricanes, it was the sixth strongest overall...

 is estimated as the costliest tropical cyclone worldwide, causing $81.2 billion in property damage (2008 USD) with overall damage estimates exceeding $100 billion (2005 USD). Katrina killed at least 1,836 people after striking Louisiana
Louisiana
Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

 and Mississippi
Mississippi
Mississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...

 as a major hurricane
Tropical cyclone scales
Tropical systems are officially ranked on one of several tropical cyclone scales according to their maximum sustained winds and in what oceanic basin they are located...

 in August 2005. Hurricane Andrew
Hurricane Andrew
Hurricane Andrew was the third Category 5 hurricane to make landfall in the United States, after the Labor Day Hurricane of 1935 and Hurricane Camille in 1969. Andrew was the first named storm and only major hurricane of the otherwise inactive 1992 Atlantic hurricane season...

 is the second most destructive tropical cyclone in U.S history, with damages totaling $40.7 billion (2008 USD), and with damage costs at $31.5 billion (2008 USD), Hurricane Ike
Hurricane Ike
Hurricane Ike was the second-costliest hurricane ever to make landfall in the United States, the costliest hurricane ever to impact Cuba and the second most active hurricane to reach the Canadian mainland in the Great Lakes Region after Hurricane Hazel in 1954...

 is the third most destructive tropical cyclone in U.S history. The Galveston Hurricane of 1900
Galveston Hurricane of 1900
The Hurricane of 1900 made landfall on the city of Galveston in the U.S. state of Texas, on September 8, 1900.It had estimated winds of at landfall, making it a Category 4 storm on the Saffir-Simpson Hurricane Scale...

 is the deadliest natural disaster in the United States, killing an estimated 6,000 to 12,000 people in Galveston, Texas
Galveston, Texas
Galveston is a coastal city located on Galveston Island in the U.S. state of Texas. , the city had a total population of 47,743 within an area of...

. Hurricane Mitch
Hurricane Mitch
Hurricane Mitch was the most powerful hurricane and the most destructive of the 1998 Atlantic hurricane season, with maximum sustained winds of 180 mph . The storm was the thirteenth tropical storm, ninth hurricane, and third major hurricane of the season. Along with Hurricane Georges, Mitch...

 caused more than 10,000 fatalities in Latin America. Hurricane Iniki
Hurricane Iniki
Hurricane Iniki was the most powerful hurricane to strike the U.S. state of Hawaii in recorded history. Forming on September 5 during the strong El Niño of 1991–1994, Iniki was one of eleven Central Pacific tropical cyclones during the 1992 season. It attained tropical storm status on...

 in 1992 was the most powerful storm to strike Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

 in recorded history, hitting Kauai
Kauai
Kauai or Kauai, known as Tauai in the ancient Kaua'i dialect, is geologically the oldest of the main Hawaiian Islands. With an area of , it is the fourth largest of the main islands in the Hawaiian archipelago, and the 21st largest island in the United States. Known also as the "Garden Isle",...

 as a Category 4 hurricane, killing six people, and causing U.S. $3 billion in damage. Kauai was also struck by Hurricanes Dot (1959) and Iwa (1982) (see List of Hawaii hurricanes). Other destructive Eastern Pacific hurricane
Pacific hurricane
A Pacific hurricane or tropical storm is a tropical cyclone that develops in the northeastern part of the Pacific Ocean. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, , central , and western...

s include Pauline
Hurricane Pauline
Hurricane Pauline was one of the strongest and deadliest Pacific hurricanes to make landfall on Mexico. The sixteenth tropical storm, eighth hurricane, and seventh major hurricane of the 1997 Pacific hurricane season, Pauline developed out of a tropical wave on October 5 about 250 miles ...

 and Kenna
Hurricane Kenna
Hurricane Kenna was the second-most intense Pacific hurricane to strike the west coast of Mexico in recorded history. Kenna was the sixteenth tropical depression, thirteenth tropical storm, seventh hurricane, sixth major hurricane, and third Category 5 hurricane of the 2002 Pacific hurricane season...

, both causing severe damage after striking Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 as major hurricanes. In March 2004, Cyclone Gafilo
Cyclone Gafilo
Cyclone Gafilo was a powerful tropical cyclone which struck Madagascar in March 2004, causing devastating damage. It is the most intense cyclone ever to form in the south-western Indian Ocean.-Meteorological history:...

 struck northeastern Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

 as a powerful cyclone, killing 74, affecting more than 200,000, and becoming the worst cyclone to affect the nation for more than 20 years.


The most intense storm on record was Typhoon Tip
Typhoon Tip
Typhoon Tip was the largest and most intense tropical cyclone on record. The nineteenth tropical storm and twelfth typhoon of the 1979 Pacific typhoon season, Tip developed out of a disturbance in the monsoon trough on October 4 near Pohnpei...

 in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870 mbar (652.5 mmHg) and maximum sustained wind speeds of 165 knots (89.8 m/s) or 190 miles per hour (305.8 km/h). Tip
Typhoon Tip
Typhoon Tip was the largest and most intense tropical cyclone on record. The nineteenth tropical storm and twelfth typhoon of the 1979 Pacific typhoon season, Tip developed out of a disturbance in the monsoon trough on October 4 near Pohnpei...

, however, does not solely hold the record for fastest sustained winds in a cyclone. Typhoon Keith in the Pacific and Hurricanes Camille
Hurricane Camille
Hurricane Camille was the third and strongest tropical cyclone and second hurricane during the 1969 Atlantic hurricane season. The second of three catastrophic Category 5 hurricanes to make landfall in the United States during the 20th century , which it did near the mouth of the Mississippi River...

 and Allen
Hurricane Allen
Hurricane Allen was the first and strongest hurricane of the 1980 Atlantic hurricane season. It was one of the strongest hurricanes in recorded history, one of the few hurricanes to reach Category 5 status on the Saffir-Simpson Hurricane Scale on three separate occasions, and spent more time...

 in the North Atlantic currently share this record with Tip. Camille was the only storm to actually strike land while at that intensity, making it, with 165 knots (89.8 m/s) or 190 miles per hour (305.8 km/h) sustained winds and 183 knots (99.6 m/s) or 210 miles per hour (338 km/h) gusts, the strongest tropical cyclone on record at landfall. Typhoon Nancy
Typhoon Nancy (1961)
Super Typhoon Nancy was a powerful tropical cyclone of the 1961 Pacific typhoon season. The system with possibly the strongest winds ever measured in a tropical cyclone, Nancy caused extensive damage and at least 173 deaths and thousands of injuries in Japan and elsewhere in September 1961...

 in 1961 had recorded wind speeds of 185 knots (100.7 m/s) or 215 miles per hour (346 km/h), but recent research indicates that wind speeds from the 1940s to the 1960s were gauged too high, and this is no longer considered the storm with the highest wind speeds on record. Likewise, a surface-level gust caused by Typhoon Paka
Typhoon Paka
Typhoon Paka was the last tropical cyclone in the 1997 Pacific Ocean hurricane and typhoon season, and was among the strongest Pacific typhoons in the month of December. Paka, which is the Hawaiian name for Pat, developed on November 28 from a trough well to the southwest of Hawaii...

 on Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...

 was recorded at 205 knots (111.6 m/s) or 235 miles per hour (378.2 km/h). Had it been confirmed, it would be the strongest non-tornadic
Tornado
A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...

 wind ever recorded on the Earth's surface, but the reading had to be discarded since the anemometer
Anemometer
An anemometer is a device for measuring wind speed, and is a common weather station instrument. The term is derived from the Greek word anemos, meaning wind, and is used to describe any airspeed measurement instrument used in meteorology or aerodynamics...

 was damaged by the storm. Hurricane Wilma
Hurricane Wilma
Hurricane Wilma was the most intense tropical cyclone ever recorded in the Atlantic basin. Wilma was the twenty-second storm , thirteenth hurricane, sixth major hurricane, and fourth Category 5 hurricane of the record-breaking 2005 season...

 is the most intense tropical cyclone in the Atlantic Basin and the strongest tropical cyclone in the Western Hemisphere.

In addition to being the most intense tropical cyclone on record, Tip was the largest cyclone on record, with tropical storm-force winds 2170 kilometres (1,348.4 mi) in diameter. The smallest storm on record, Tropical Storm Marco
Tropical Storm Marco (2008)
Tropical Storm Marco was the smallest known tropical cyclone on record. The thirteenth named storm of the 2008 Atlantic hurricane season, Marco developed out of a broad area of low pressure over the northwestern Caribbean during late September 2008. Influenced by a tropical wave on October 4,...

, formed during October 2008, and made landfall in Veracruz
Veracruz
Veracruz, formally Veracruz de Ignacio de la Llave officially Estado Libre y Soberano de Veracruz de Ignacio de la Llave , is one of the 31 states that, along with the Federal District, comprise the 32 federative entities of Mexico. It is divided in 212 municipalities and its capital city is...

. Marco generated tropical storm-force winds only 37 kilometres (23 mi) in diameter.

Hurricane John
Hurricane John (1994)
Hurricane John formed during the 1994 Pacific hurricane season and became both the longest-lasting and the farthest-traveling tropical cyclone ever observed...

 is the longest-lasting tropical cyclone on record, lasting 31 days in 1994
1994 Pacific hurricane season
The 1994 Pacific hurricane season officially started on May 15, 1994 in the eastern Pacific, and on June 1, 1994 in the central Pacific, and lasted until November 30, 1994. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean...

. Before the advent of satellite imagery in 1961, however, many tropical cyclones were underestimated in their durations. John is also the longest-tracked tropical cyclone in the Northern Hemisphere on record, which had a path of 7,165 miles (13,280 km). Reliable data for Southern Hemisphere cyclones is unavailable.

Changes caused by El Niño-Southern Oscillation



Most tropical cyclones form on the side of the subtropical ridge closer to the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

, then move poleward past the ridge axis before recurving into the main belt of the Westerlies
Westerlies
The Westerlies, anti-trades, or Prevailing Westerlies, are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. These prevailing winds blow from the west to the east, and steer extratropical...

. When the subtropical ridge
Subtropical ridge
The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

 position shifts due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 and Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

 tend to experience much fewer September–November tropical cyclone impacts during El Niño and neutral years. During El Niño years, the break in the subtropical ridge tends to lie near 130°E
130th meridian east
The meridian 130° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, Australia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole....

 which would favor the Japanese archipelago. During El Niño years, Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...

's chance of a tropical cyclone impact is one-third of the long term average. The tropical Atlantic ocean experiences depressed activity due to increased vertical wind shear
Wind shear
Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...

 across the region during El Niño years. During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific ocean, which increases the landfall threat to China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

.

Long-term activity trends




While the number of storms in the Atlantic has increased since 1995, there is no obvious global trend; the annual number of tropical cyclones worldwide remains about 87 ± 10 (Between 77 and 97 tropical cyclones annually). However, the ability of climatologists to make long-term data analysis in certain basins is limited by the lack of reliable historical data in some basins, primarily in the Southern Hemisphere. In spite of that, there is some evidence that the intensity of hurricanes is increasing. Kerry Emanuel
Kerry Emanuel
Kerry Emanuel is an American professor of meteorology currently working at the Massachusetts Institute of Technology in Cambridge. In particular he has specialized in atmospheric convection and the mechanisms acting to intensify hurricanes. He coined the term "hypercane" in 1994. In 2007, he was...

 stated, "Records of hurricane activity worldwide show an upswing of both the maximum wind speed in and the duration of hurricanes. The energy released by the average hurricane (again considering all hurricanes worldwide) seems to have increased by around 70% in the past 30 years or so, corresponding to about a 15% increase in the maximum wind speed and a 60% increase in storm lifetime."

Atlantic storms are becoming more destructive financially, since five of the ten most expensive storms in United States history have occurred since 1990. According to the World Meteorological Organization
World Meteorological Organization
The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

, “recent increase in societal impact from tropical cyclones has been caused largely by rising concentrations of population and infrastructure in coastal regions.” Pielke et al. (2008) normalized mainland U.S. hurricane damage from 1900–2005 to 2005 values and found no remaining trend of increasing absolute damage. The 1970s and 1980s were notable because of the extremely low amounts of damage compared to other decades. The decade 1996–2005 was the second most damaging among the past 11 decades, with only the decade 1926–1935 surpassing its costs. The most damaging single storm is the 1926 Miami hurricane
1926 Miami Hurricane
The 1926 Miami hurricane was a Category 4 hurricane that devastated Miami in September 1926. The storm also caused significant damage in the Florida Panhandle, the U.S. state of Alabama, and the Bahamas...

, with $157 billion of normalized damage.

Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast may have gone unmeasured in some instances. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect.

The number and strength of Atlantic hurricanes may undergo a 50–70 year cycle, also known as the Atlantic Multidecadal Oscillation
Atlantic Multidecadal Oscillation
The Atlantic multidecadal oscillation is a mode of variability occurring in the North Atlantic Ocean and which has its principal expression in the sea surface temperature field...

. Nyberg et al. reconstructed Atlantic major hurricane activity back to the early 18th century and found five periods averaging 3–5 major hurricanes per year and lasting 40–60 years, and six other averaging 1.5–2.5 major hurricanes per year and lasting 10–20 years. These periods are associated with the Atlantic multidecadal oscillation. Throughout, a decadal oscillation related to solar irradiance was responsible for enhancing/dampening the number of major hurricanes by 1–2 per year.

Although more common since 1995, few above-normal hurricane seasons occurred during 1970–94. Destructive hurricanes struck frequently from 1926–60, including many major New England hurricanes. Twenty-one Atlantic tropical storms formed in 1933
1933 Atlantic hurricane season
The 1933 Atlantic hurricane season was the second most active Atlantic hurricane season on record, with 21 storms forming during that year in the northwest Atlantic Ocean. The season ran through the summer and the first half of fall in 1933, and was surpassed in total number of tropical cyclones by...

, a record only recently exceeded in 2005
2005 Atlantic hurricane season
The 2005 Atlantic hurricane season was the most active Atlantic hurricane season in recorded history, repeatedly shattering numerous records. The impact of the season was widespread and ruinous with an estimated 3,913 deaths and record damage of about $159.2 billion...

, which saw 28 storms. Tropical hurricanes occurred infrequently during the seasons of 1900–25; however, many intense storms formed during 1870–99. During the 1887 season
1887 Atlantic hurricane season
Another May storm formed south of Jamaica on May 17, way outside of the season and moved generally northward. It crossed Cuba on the 19th as a tropical storm, and moved out to sea. Two peaked at twice, once on May 18 and May 20. Two dissipated on the 21st in the Atlantic Ocean...

, 19 tropical storms formed, of which a record 4 occurred after 1 November and 11 strengthened into hurricanes. Few hurricanes occurred in the 1840s to 1860s; however, many struck in the early 19th century, including a 1821 storm
1821 Norfolk and Long Island Hurricane
The 1821 Norfolk and Long Island Hurricane was one of four known tropical cyclones that have made landfall in New York City. Another, even more intense hurricane struck the region in pre-Columbian times and was detected by paleotempestological research...

 that made a direct hit on New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

. Some historical weather experts say these storms may have been as high as Category 4
Saffir-Simpson Hurricane Scale
The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...

 in strength.

These active hurricane seasons predated satellite coverage of the Atlantic basin. Before the satellite era began in 1960, tropical storms or hurricanes went undetected unless a reconnaissance aircraft encountered one, a ship reported a voyage through the storm, or a storm hit land in a populated area. The official record, therefore, could miss storms in which no ship experienced gale-force winds, recognized it as a tropical storm (as opposed to a high-latitude extra-tropical cyclone, a tropical wave, or a brief squall), returned to port, and reported the experience.

Proxy records based on paleotempestological
Paleotempestology
Paleotempestology is the study of past tropical cyclone activity by means of geological proxies as well as historical documentary records. The term was coined by Kerry Emanuel.-Sedimentary proxy records:...

 research have revealed that major hurricane activity along the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

 coast varies on timescales of centuries to millennia. Few major hurricanes struck the Gulf coast during 3000–1400 BC and again during the most recent millennium. These quiescent intervals were separated by a hyperactive period during 1400 BC and 1000 AD, when the Gulf coast was struck frequently by catastrophic hurricanes and their landfall probabilities increased by 3–5 times. This millennial-scale variability has been attributed to long-term shifts in the position of the Azores High
Azores High
The Azores High is a large subtropical semi-permanent centre of high atmospheric pressure found near the Azores in the Atlantic Ocean, at the Horse latitudes...

, which may also be linked to changes in the strength of the North Atlantic Oscillation
North Atlantic oscillation
The North Atlantic oscillation is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through east-west oscillation motions of the Icelandic low and the Azores high, it controls the...

.

According to the Azores High hypothesis, an anti-phase pattern is expected to exist between the Gulf of Mexico coast and the Atlantic coast. During the quiescent periods, a more northeasterly position of the Azores High would result in more hurricanes being steered towards the Atlantic coast. During the hyperactive period, more hurricanes were steered towards the Gulf coast as the Azores High was shifted to a more southwesterly position near the Caribbean. Such a displacement of the Azores High is consistent with paleoclimatic evidence that shows an abrupt onset of a drier climate in Haiti
Haiti
Haiti , officially the Republic of Haiti , is a Caribbean country. It occupies the western, smaller portion of the island of Hispaniola, in the Greater Antillean archipelago, which it shares with the Dominican Republic. Ayiti was the indigenous Taíno or Amerindian name for the island...

 around 3200 14C
Radiocarbon dating
Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...

 years BP, and a change towards more humid conditions in the Great Plains
Great Plains
The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...

 during the late-Holocene as more moisture was pumped up the Mississippi Valley through the Gulf coast. Preliminary data from the northern Atlantic coast seem to support the Azores High hypothesis. A 3000-year proxy record from a coastal lake in Cape Cod
Cape Cod
Cape Cod, often referred to locally as simply the Cape, is a cape in the easternmost portion of the state of Massachusetts, in the Northeastern United States...

 suggests that hurricane activity increased significantly during the past 500–1000 years, just as the Gulf coast was amid a quiescent period of the last millennium.

Global warming


The U.S. National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

 Geophysical Fluid Dynamics Laboratory
Geophysical Fluid Dynamics Laboratory
The Geophysical Fluid Dynamics Laboratory is a laboratory in the National Oceanic and Atmospheric Administration /Office of Oceanic and Atmospheric Research . The current director is Dr. V...

 performed a simulation to determine if there is a statistical
Statistics
Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....

 trend
Periodic trends
In Chemistry, periodic trends are the tendencies of certain elemental characteristics to increase or decrease as one progresses along a row or column of the periodic table of elements.-Atomic radius:...

 in the frequency or strength of tropical cyclones over time. The simulation concluded "the strongest hurricanes in the present climate may be upstaged by even more intense hurricanes over the next century as the earth's climate is warmed by increasing levels of greenhouse gases in the atmosphere".

In an article in Nature
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

, Kerry Emanuel
Kerry Emanuel
Kerry Emanuel is an American professor of meteorology currently working at the Massachusetts Institute of Technology in Cambridge. In particular he has specialized in atmospheric convection and the mechanisms acting to intensify hurricanes. He coined the term "hypercane" in 1994. In 2007, he was...

 stated that potential hurricane destructiveness, a measure combining hurricane strength, duration, and frequency, "is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multidecadal oscillations in the North Atlantic and North Pacific, and global warming". Emanuel predicted "a substantial increase in hurricane-related losses in the twenty-first century". In more recent work published by Emanuel (in the March 2008 issue of the Bulletin of the American Meteorological Society), he states that new climate modeling data indicates “global warming should reduce the global frequency of hurricanes.” According to the Houston Chronicle, the new work suggests that, even in a dramatically warming world, hurricane frequency and intensity may not substantially rise during the next two centuries.

Likewise, P.J. Webster and others published an article in Science
Science (journal)
Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....

examining the "changes in tropical cyclone number, duration, and intensity" over the past 35 years, the period when satellite data has been available. Their main finding was although the number of cyclones decreased throughout the planet excluding the north Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

, there was a great increase in the number and proportion of very strong cyclones.
The strength of the reported effect is surprising in light of modeling studies that predict only a one-half category increase in storm intensity as a result of a ~2 °C (3.6 °F) global warming. Such a response would have predicted only a ~10% increase in Emanuel's potential destructiveness index during the 20th century rather than the ~75–120% increase he reported. Second, after adjusting for changes in population and inflation, and despite a more than 100% increase in Emanuel's potential destructiveness index, no statistically significant increase in the monetary damages resulting from Atlantic hurricanes has been found.

Sufficiently warm sea surface temperatures are considered vital to the development of tropical cyclones. Although neither study can directly link hurricanes with global warming, the increase in sea surface temperatures is believed to be due to both global warming and natural variability, e.g. the hypothesized Atlantic Multidecadal Oscillation
Atlantic Multidecadal Oscillation
The Atlantic multidecadal oscillation is a mode of variability occurring in the North Atlantic Ocean and which has its principal expression in the sea surface temperature field...

 (AMO), although an exact attribution has not been defined. However, recent temperatures are the warmest ever observed for many ocean basins.

In February 2007, the United Nations
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

 Intergovernmental Panel on Climate Change
Intergovernmental Panel on Climate Change
The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

 released its fourth assessment report
IPCC Fourth Assessment Report
Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for...

 on climate change
Climate change
Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

. The report noted many observed changes in the climate, including atmospheric composition, global average temperatures, ocean conditions, among others. The report concluded the observed increase in tropical cyclone intensity is larger than climate models predict. In addition, the report considered that it is likely that storm intensity will continue to increase through the 21st century, and declared it more likely than not that there has been some human contribution to the increases in tropical cyclone intensity. However, there is no universal agreement about the magnitude of the effects anthropogenic global warming has on tropical cyclone formation, track, and intensity. For example, critics such as Chris Landsea assert that man-made effects would be "quite tiny compared to the observed large natural hurricane variability". A statement by the American Meteorological Society
American Meteorological Society
The American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, the American Meteorological Society has a membership...

 on 1 February 2007 stated that trends in tropical cyclone records offer "evidence both for and against the existence of a detectable anthropogenic signal" in tropical cyclogenesis
Tropical cyclogenesis
Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

. Although many aspects of a link between tropical cyclones and global warming are still being "hotly debated", a point of agreement is that no individual tropical cyclone or season can be attributed to global warming. Research reported in the 3 September 2008 issue of Nature found that the strongest tropical cyclones are getting stronger, in particular over the North Atlantic and Indian oceans. Wind speeds for the strongest tropical storms increased from an average of 140 miles per hour (225.3 km/h) in 1981 to 156 miles per hour (251.1 km/h) in 2006, while the ocean temperature, averaged globally over the all regions where tropical cyclones form, increased from 28.2 °C (82.8 °F) to 28.5 °C (83.3 °F) during this period.

Related cyclone types




In addition to tropical cyclones, there are two other classes of cyclones within the spectrum of cyclone types. These kinds of cyclones, known as extratropical cyclone
Extratropical cyclone
Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

s and subtropical cyclone
Subtropical cyclone
A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...

s, can be stages a tropical cyclone passes through during its formation
Tropical cyclogenesis
Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

 or dissipation. An extratropical cyclone is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses; although not as frequently, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone. From space, extratropical storms have a characteristic "comma
Comma (punctuation)
The comma is a punctuation mark. It has the same shape as an apostrophe or single closing quotation mark in many typefaces, but it differs from them in being placed on the baseline of the text. Some typefaces render it as a small line, slightly curved or straight but inclined from the vertical, or...

-shaped" cloud pattern. Extratropical cyclones can also be dangerous when their low-pressure centers cause powerful winds and high seas.

A subtropical cyclone is a weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...

 system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form in a wide band of latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

s, from the equator
Equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

 to 50°. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm. From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.

Tropical cyclones in popular culture



In popular culture
Popular culture
Popular culture is the totality of ideas, perspectives, attitudes, memes, images and other phenomena that are deemed preferred per an informal consensus within the mainstream of a given culture, especially Western culture of the early to mid 20th century and the emerging global mainstream of the...

, tropical cyclones have made appearances in different types of media, including films, books, television, music, and electronic game
Electronic game
An electronic game is a game that employs electronics to create an interactive system with which a player can play. The most common form of electronic game today is the video game, and for this reason the terms are often mistakenly used synonymously. Other common forms of electronic game include...

s. The media can have tropical cyclones that are entirely fiction
Fiction
Fiction is the form of any narrative or informative work that deals, in part or in whole, with information or events that are not factual, but rather, imaginary—that is, invented by the author. Although fiction describes a major branch of literary work, it may also refer to theatrical,...

al, or can be based on real events. For example, George Rippey Stewart's Storm
Storm (novel)
Storm is a novel written by George Rippey Stewart and published in 1941. The book became a best-seller and helped lead to the naming of tropical cyclones worldwide, even though the main character of the book was an extratropical cyclone.-Plot summary:...

, a best-seller published in 1941, is thought to have influenced meteorologists into giving female names to Pacific tropical cyclones. Another example is the hurricane in The Perfect Storm
The Perfect Storm (film)
The Perfect Storm is a 2000 dramatic disaster film directed by Wolfgang Petersen. It is an adaptation of the 1997 non-fiction book of the same title by Sebastian Junger about the crew of the Andrea Gail that got caught in the Perfect Storm of 1991. The film stars George Clooney, Mark Wahlberg,...

, which describes the sinking of the Andrea Gail
Andrea Gail
The F/V Andrea Gail was a commercial fishing vessel that was lost at sea with all hands during the "Perfect Storm" of 1991. The vessel and her six-man crew had been fishing the North Atlantic Ocean out of Gloucester, Massachusetts. Her last reported position was northeast of Sable Island on...

by the 1991 Perfect Storm. Also, hypothetical hurricanes have been featured in parts of the plots of series such as The Simpsons
Hurricane Neddy
"Hurricane Neddy" is the eighth episode of The Simpsons eighth season which originally aired December 29, 1996. It was written by Steve Young, directed by Bob Anderson and features a cameo by Jon Lovitz as Jay Sherman from The Critic. In this episode, "Hurricane Barbara" viciously strikes...

, Invasion
Invasion (TV series)
Invasion is an American science fiction television series that aired on ABC for only one season beginning in September 2005. Somewhat similar to Invasion of the Body Snatchers, the show told the story of the aftermath of a hurricane in which water-based creatures infiltrate a small Florida town and...

, Family Guy, Seinfeld
The Checks
"The Checks" is the 141st episode of the sitcom Seinfeld. This was the 7th episode for the 8th season. It aired on NBC on November 7, 1996.-Plot:...

, Dawson's Creek
Dawson's Creek
Dawson's Creek is an American teen drama television series which debuted on January 20, 1998, on The WB Television Network and was produced by Sony Pictures Television. The show is set in the fictional seaside town of Capeside, Massachusetts, and in Boston, Massachusetts, during the later seasons...

, and CSI: Miami
CSI: Miami (season 2)
The second season of CSI: Miami premiered on CBS on September 22, 2003 and ended May 24, 2004.-Notable cast members:-Episodes:...

. The 2004 film The Day After Tomorrow
The Day After Tomorrow
The Day After Tomorrow is a 2004 American science-fiction disaster film that depicts the catastrophic effects of global warming in a series of extreme weather events that usher in global cooling which leads to a new ice age. The film did well at the box office, grossing $542,771,772 internationally...

includes several mentions of actual tropical cyclones as well as featuring fantastical "hurricane-like" non-tropical Arctic storms.

See also



  • Cyclone
    Cyclone
    In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...

  • Disaster preparedness
  • HURDAT
    HURDAT
    The North Atlantic hurricane database, or HURDAT, is the database for all tropical cyclones in the Atlantic Ocean, Gulf of Mexico and Caribbean Sea, since 1851.-History:...

     (online database)
  • Hurricane Alley
    Hurricane Alley
    Hurricane Alley is an area of warm water in the Atlantic Ocean stretching from the west coast of northern Africa to the east coast of central America and Gulf Coast of the southern United States. Many hurricanes form within this area...

  • Saffir–Simpson Hurricane Scale

  • Hypercane
    Hypercane
    A hypercane is a hypothetical class of extreme hurricane that could form if ocean temperatures reached around , which is warmer than the warmest ocean temperature ever recorded. Such an increase could be caused by a large asteroid or comet impact, a large volcanic, supervolcanic eruption, or very...

  • List of wettest tropical cyclones by country
  • Secondary flow in tropical cyclones


Annual seasons
  • List of Atlantic hurricane seasons (current)
  • List of North Indian Ocean cyclone seasons (current)
  • List of Pacific hurricane seasons (current)
  • List of Pacific typhoon seasons (current)
  • List of South-West Indian Ocean cyclone seasons (-
    {{Redirect|Hurricane}}
    {{pp-move-indef}}
    A tropical cyclone is a storm system
    Storm
    A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...

     characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclone
    Cyclone
    In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...

    s strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation
    Condensation
    Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

     of water vapor
    Water vapor
    Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

     contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easter
    Nor'easter
    A nor'easter is a type of macro-scale storm along the East Coast of the United States and Atlantic Canada, so named because the storm travels to the northeast from the south and the winds come from the northeast, especially in the coastal areas of the Northeastern United States and Atlantic Canada...

    s, European windstorm
    European windstorm
    A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

    s, and polar low
    Polar low
    A polar low is a small-scale, long-lived atmospheric low pressure system that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. The systems usually have a horizontal length scale of less than and exist for no more than a couple of days. ...

    s. The characteristic that separates tropical cyclones from other cyclonic systems is that at any height in the atmosphere, the center of a tropical cyclone will be warmer than its surroundings; a phenomenon called "warm core" storm systems.

    The term "tropical" refers both to the geographical origin of these systems, which usually form in tropical
    Tropics
    The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

     regions of the globe, and to their formation in maritime tropical air masses. The term "cyclone" refers to such storms' cyclonic nature, with counterclockwise wind flow in the Northern Hemisphere
    Northern Hemisphere
    The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

     and clockwise wind flow in the Southern Hemisphere
    Southern Hemisphere
    The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

    . The opposite direction of the wind flow is a result of the Coriolis force. Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane (ˈhʌrɨkeɪn, ˈhʌrɨkən), typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone.

    While tropical cyclones can produce extremely powerful winds and torrential rain
    Rain
    Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...

    , they are also able to produce high waves and damaging storm surge
    Storm surge
    A storm surge is an offshore rise of water associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea...

     as well as spawning tornadoes. They develop over large bodies of warm water, and lose their strength if they move over land due to increased surface friction and loss of the warm ocean as an energy source. This is why coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal flood
    Flood
    A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

    ing up to 40 kilometres (24.9 mi) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can relieve drought
    Drought
    A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...

     conditions. They also carry heat energy away from the tropics and transport it toward temperate
    Temperate
    In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...

     latitudes, which makes them an important part of the global atmospheric circulation
    Atmospheric circulation
    Atmospheric circulation is the large-scale movement of air, and the means by which thermal energy is distributed on the surface of the Earth....

     mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere
    Troposphere
    The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

    , and to maintain a relatively stable and warm temperature worldwide.

    Many tropical cyclones develop
    Tropical cyclogenesis
    Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

     when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. The background environment is modulated by climatological cycles and patterns such as the Madden-Julian oscillation
    Madden-Julian oscillation
    The Madden–Julian oscillation ' is the largest element of the intraseasonal variability in the tropical atmosphere. It is a large-scale coupling between atmospheric circulation and tropical deep convection...

    , El Niño-Southern Oscillation
    El Niño-Southern Oscillation
    El Niño/La Niña-Southern Oscillation, or ENSO, is a quasiperiodic climate pattern that occurs across the tropical Pacific Ocean roughly every five years...

    , and the Atlantic multidecadal oscillation
    Atlantic Multidecadal Oscillation
    The Atlantic multidecadal oscillation is a mode of variability occurring in the North Atlantic Ocean and which has its principal expression in the sea surface temperature field...

    . Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere
    Troposphere
    The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

    ; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an eye
    Eye (cyclone)
    The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...

    . On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. It is not possible to artificially induce the dissipation of these systems with current technology.
    {{Tropicalcyclone}}

    Physical structure


    {{See also|Eye (cyclone)}}

    All tropical cyclones are areas of low
    Low pressure area
    A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...

     atmospheric pressure
    Atmospheric pressure
    Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

     in the Earth's atmosphere. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at sea level
    Sea level
    Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

    . Tropical cyclones are characterized and driven by the release of large amounts of latent heat of condensation, which occurs when moist air is carried upwards and its water vapor
    Water vapor
    Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

     condenses. This heat is distributed vertically around the center of the storm. Thus, at any given altitude (except close to the surface, where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.

    Eye and center


    A strong tropical cyclone will harbor an area of sinking air at the center of circulation. If this area is strong enough, it can develop into a large "eye". Weather in the eye is normally calm and free of clouds, although the sea may be extremely violent. The eye is normally circular in shape, and is typically 30–65 km (20–40 miles) in diameter
    Diameter
    In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

    , though eyes as small as 3 kilometres (1.9 mi) and as large as 370 kilometres (229.9 mi) have been observed. Intense, mature tropical cyclones can sometimes exhibit an outward curving of the eyewall's top, making it resemble an arena football stadium; this phenomenon is thus sometimes referred to as the stadium effect. It is usually coldest in the center.

    There are other features that either surround the eye, or cover it. The central dense overcast is the concentrated area of strong thunderstorm activity near the center of a tropical cyclone; in weaker tropical cyclones, the CDO may cover the center completely. The eyewall is a circle of strong thunderstorms that surrounds the eye; here is where the greatest wind speeds are found, where clouds reach the highest, and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land. Eyewall replacement cycles occur naturally in intense tropical cyclones. When cyclones reach peak intensity they usually have an eyewall and radius of maximum wind
    Radius of maximum wind
    The radius of maximum wind is the distance between the center of a cyclone and its band of strongest winds. It is a parameter in atmospheric dynamics and tropical cyclone forecasting. The highest rainfall rates occur near the RMW of tropical cyclones. The extent of a cyclone's storm surge and...

    s that contract to a very small size, around 10 kilometres (6.2 mi) to 25 kilometres (15.5 mi). Outer rainbands can organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and angular momentum
    Angular momentum
    In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...

    . When the inner eyewall weakens, the tropical cyclone weakens (in other words, the maximum sustained winds weaken and the central pressure rises.) The outer eyewall replaces the inner one completely at the end of the cycle. The storm can be of the same intensity as it was previously or even stronger after the eyewall replacement cycle finishes. The storm may strengthen again as it builds a new outer ring for the next eyewall replacement.
    Size descriptions of tropical cyclones
    ROCI Type
    Less than 2 degrees latitude Very small/midget
    2 to 3 degrees of latitude Small
    3 to 6 degrees of latitude Medium/Average
    6 to 8 degrees of latitude Large
    Over 8 degrees of latitude Very large

    Size


    One measure of the size of a tropical cyclone is determined by measuring the distance from its center of circulation to its outermost closed isobar, also known as its ROCI
    Radius of outermost closed isobar
    style="float: right; clear: right; background-color: transparent; margin-left: 0em"|The radius of outermost closed isobar is one of the quantities used to determine the size of a tropical cyclone. It is determined by measuring the radii from the center of the storm to its outermost closed isobar...

    . If the radius is less than two degrees of latitude
    Latitude
    In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

     or 222 kilometres (137.9 mi), then the cyclone is "very small" or a "midget". A radius between 3 and 6 latitude degrees or 333 kilometres (206.9 mi) to 670 kilometres (416.3 mi) are considered "average-sized". "Very large" tropical cyclones have a radius of greater than 8 degrees or 888 kilometres (551.8 mi). Use of this measure has objectively determined that tropical cyclones in the northwest Pacific Ocean are the largest on earth on average, with Atlantic tropical cyclones roughly half their size. Other methods of determining a tropical cyclone's size include measuring the radius of gale force winds and measuring the radius at which its relative vorticity field decreases to 1×10−5 s−1 from its center.

    Mechanics


    A tropical cyclone's primary energy source is the release of the heat of condensation from water vapor condensing
    Condensation
    Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

    , with solar heating being the initial source for evaporation. Therefore, a tropical cyclone can be visualized as a giant vertical heat engine
    Heat engine
    In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...

     supported by mechanics driven by physical forces such as the rotation
    Rotation
    A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

     and gravity of the Earth. In another way, tropical cyclones could be viewed as a special type of mesoscale convective complex
    Mesoscale Convective Complex
    A mesoscale convective complex is a unique kind of mesoscale convective system which is defined by characteristics observed in infrared satellite imagery. They are long-lived, nocturnal in formation and commonly contain heavy rainfall, wind, hail, lightning and possibly tornadoes.-Size:A...

    , which continues to develop over a vast source of relative warmth and moisture. While an initial warm core system, such as an organized thunderstorm complex, is necessary for the formation of a tropical cyclone, a large flux of energy is needed to lower atmospheric pressure
    Atmospheric pressure
    Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

     more than a few millibars (0.10 inch of mercury
    Mercury (element)
    Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

    ). The inflow
    Inflow (meteorology)
    Inflow is the flow of a fluid into a large collection of that fluid. Within meteorology, inflow normally refers to the influx of warmth and moisture from air within the Earth's atmosphere into storm systems. Extratropical cyclones are fed by inflow focused along their cold front and warm fronts...

     of warmth and moisture from the underlying ocean surface is critical for tropical cyclone strengthening. A significant amount of the inflow in the cyclone is in the lowest 1 kilometres (3,280.8 ft) of the atmosphere.

    Condensation leads to higher wind speeds, as a tiny fraction of the released energy is converted into mechanical energy; the faster winds and lower pressure associated with them in turn cause increased surface evaporation and thus even more condensation. Much of the released energy drives updrafts
    Vertical draft
    An updraft or downdraft is the vertical movement of air as a weather related phenomenon. One of two forces causes the air to move. Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding region, and so will rise...

     that increase the height of the storm clouds, speeding up condensation. This positive feedback loop, called the Wind-induced surface heat exchange
    Wind-induced surface heat exchange
    The wind-induced surface heat exchange is a positive feedback mechanism between the ocean and atmosphere in which a stronger ocean-to-atmosphere heat flux results in a stronger atmospheric circulation, which results in a strong heat flux. It has been hypothesized that this is the mechanism that...

    , continues for as long as conditions are favorable for tropical cyclone development
    Tropical cyclogenesis
    Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

    . Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. The rotation of the Earth causes the system to spin, an effect known as the Coriolis effect
    Coriolis effect
    In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

    , giving it a cyclonic characteristic and affecting the trajectory of the storm. In the Northern Hemisphere
    Northern Hemisphere
    The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

    , where the cyclone's wind flow is counterclockwise, the fastest winds relative to the surface of the Earth occur on the eastern side of a northward-moving storm and on the northern side of a westward-moving one; the opposite occurs in the Southern Hemisphere
    Southern Hemisphere
    The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

    , where the wind flow is clockwise
    Clockwise
    Circular motion can occur in two possible directions. A clockwise motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back to the top...

    .

    What primarily distinguishes tropical cyclones from other meteorological phenomena is deep convection
    Deep convection
    Deep convection is a convective process in a medium, usually in an atmosphere or ocean, that in some sense spans the vertical.Within the atmosphere, this means from the surface to above the 500 hPa level, generally stopping at or defining the tropopause at around 200 hPa...

     as a driving force. Because convection is strongest in a tropical climate
    Tropical climate
    A tropical climate is a climate of the tropics. In the Köppen climate classification it is a non-arid climate in which all twelve months have mean temperatures above...

    , it defines the initial domain of the tropical cyclone. By contrast, mid-latitude cyclone
    Mid-latitude cyclone
    Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere . Cyclogenesis is an umbrella term for several different processes, all of which result in the development of some sort of cyclone. It can occur at various scales, from the microscale to the synoptic scale...

    s draw their energy mostly from pre-existing horizontal temperature gradient
    Gradient
    In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....

    s in the atmosphere. To continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the needed atmospheric moisture to keep the positive feedback loop running. When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly.


    The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, which can influence subsequent cyclone development. This cooling is primarily caused by wind-driven mixing of cold water from deeper in the ocean and the warm surface waters. This effect results in a negative feedback process that can inhibit further development or lead to weakening. Additional cooling may come in the form of cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days.

    Scientists estimate that a tropical cyclone releases heat energy at the rate of 50 to 200 exajoules (1018 J) per day, equivalent to about 1 PW (1015 watt). This rate of energy release is equivalent to 70 times the world energy consumption
    World energy resources and consumption
    ]World energy consumption in 2010: over 5% growthEnergy markets have combined crisis recovery and strong industry dynamism. Energy consumption in the G20 soared by more than 5% in 2010, after the slight decrease of 2009. This strong increase is the result of two converging trends...

     of humans and 200 times the worldwide electrical generating capacity, or to exploding a 10-megaton
    TNT equivalent
    TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

     nuclear bomb every 20 minutes.

    In the lower troposphere, the most obvious motion of clouds is toward the center. However tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine. This outflow produces high, cirrus cloud
    Cirrus cloud
    Cirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...

    s that spiral away from the center. The clouds thin as they move outwards from the center of the system and are evaporated. They may be thin enough for the sun to be visible through them. These high cirrus clouds may be the first signs of an approaching tropical cyclone. As air parcels are lifted within the eye of the storm the vorticity is reduced, causing the outflow from a tropical cyclone to have anti-cyclonic motion.

    Major basins and related warning centers


    {{Main|Tropical cyclone basins|Regional Specialized Meteorological Center}}
    Basins and WMO
    World Meteorological Organization
    The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

     Monitoring Institutions
    Basin Responsible RSMCs and TCWCs
    North Atlantic National Hurricane Center
    National Hurricane Center
    The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...

     (United States)
    North-East Pacific National Hurricane Center
    National Hurricane Center
    The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...

     (United States)
    North-Central Pacific Central Pacific Hurricane Center
    Central Pacific Hurricane Center
    The Central Pacific Hurricane Center of the United States National Weather Service is the official body responsible for tracking and issuing tropical cyclone warnings, watches, advisories, discussions, and statements for the Central North Pacific Basin...

     (United States)
    North-West Pacific Japan Meteorological Agency
    Japan Meteorological Agency
    The or JMA, is the Japanese government's weather service. Charged with gathering and reporting weather data and forecasts in Japan, it is a semi-autonomous part of the Ministry of Land, Infrastructure and Transport...

    North Indian Ocean India Meteorological Department
    India Meteorological Department
    The India Meteorological Department , also referred to as the Met Office, is an agency of the Ministry of Earth Sciences of the Government of India. It is the principal agency responsible for meteorological observations, weather forecasting and seismology...

    South-West Indian Ocean Météo-France
    Météo-France
    Météo-France is the French national meteorological service.The organisation was established by decree in June 1993 and is a department of the Ministry of Transportation. It is headquartered in Paris but many domestic operations have been decentralised to Toulouse...

    Australian region Bureau of Meteorology
    Bureau of Meteorology
    The Bureau of Meteorology is an Executive Agency of the Australian Government responsible for providing weather services to Australia and surrounding areas. It was established in 1906 under the Meteorology Act, and brought together the state meteorological services that existed before then...

    (Australia)
    Meteorological and Geophysical Agency (Indonesia)
    Papua New Guinea National Weather Service
    Southern Pacific Fiji Meteorological Service
    Fiji Meteorological Service
    The Fiji Meteorological Service is a Department of the government of Fiji responsible for providing weather forecasts and is based in Nadi. Since 1995, FMS has been responsible for naming and tracking tropical cyclones in the Southwest Pacific region...


    Meteorological Service of New Zealand
    : Indicates a Tropical Cyclone Warning Center


    There are six Regional Specialized Meteorological Center
    Regional Specialized Meteorological Center
    A Regional Specialized Meteorological Centre is responsible for the distribution of information, advisories, and warnings regarding the specific program they have a part of, agreed by consensus at the World Meteorological Organization as part of the World Weather Watch.-Tropical...

    s (RSMCs) worldwide. These organizations are designated by the World Meteorological Organization
    World Meteorological Organization
    The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

     and are responsible for tracking and issuing bulletins, warnings, and advisories about tropical cyclones in their designated areas of responsibility. In addition, there are six Tropical Cyclone Warning Centers (TCWCs) that provide information to smaller regions. The RSMCs and TCWCs are not the only organizations that provide information about tropical cyclones to the public. The Joint Typhoon Warning Center
    Joint Typhoon Warning Center
    The Joint Typhoon Warning Center is a joint United States Navy – United States Air Force task force located at the Naval Maritime Forecast Center in Pearl Harbor, Hawaii...

     (JTWC) issues advisories in all basins except the Northern Atlantic for the purposes of the United States Government. The Philippine Atmospheric, Geophysical and Astronomical Services Administration
    Philippine Atmospheric, Geophysical and Astronomical Services Administration
    The Philippine Atmospheric, Geophysical and Astronomical Services Administration is a Philippine national institution dedicated to provide flood and typhoon warnings, public weather forecasts and advisories, meteorological, astronomical, climatological, and other specialized information and...

     (PAGASA) issues advisories and names for tropical cyclones that approach the Philippines
    Philippines
    The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

     in the Northwestern Pacific to protect the life and property of its citizens. The Canadian Hurricane Center (CHC) issues advisories on hurricanes and their remnants for Canadian citizens when they affect Canada.

    On 26 March 2004, Cyclone Catarina
    Cyclone Catarina
    Cyclone Catarina is one of several informal names for a South Atlantic tropical cyclone that hit southeastern Brazil in late March 2004. The storm developed out of a stationary cold-core upper-level trough on March 12...

     became the first recorded South Atlantic cyclone
    South Atlantic tropical cyclone
    South Atlantic tropical cyclones are unusual weather events that occur in the southern hemisphere. Strong wind shear and a lack of weather disturbances favorable for tropical cyclone development make any hurricane-strength cyclones extremely rare...

     and subsequently struck southern Brazil
    Brazil
    Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

     with winds equivalent to Category 2 on the Saffir-Simpson Hurricane Scale
    Saffir-Simpson Hurricane Scale
    The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...

    . As the cyclone formed outside the authority of another warning center, Brazilian meteorologists initially treated the system as an extratropical cyclone
    Extratropical cyclone
    Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

    , although subsequently classified it as tropical.

    Formation


    {{Main|Tropical cyclogenesis}}


    Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active while November is the only month with all the tropical cyclone basins active.

    Times


    In the Northern Atlantic Ocean
    Atlantic Ocean
    The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

    , a distinct cyclone season
    Atlantic hurricane season
    The Atlantic hurricane season is the period in a year when hurricanes usually form in the Atlantic Ocean. Tropical cyclones in the North Atlantic are called hurricanes, tropical storms, or tropical depressions. In addition, there have been several storms over the years that have not been fully...

     occurs from June 1 to November 30, sharply peaking from late August through September. The statistical peak of the Atlantic hurricane season is 10 September. The Northeast Pacific Ocean
    Pacific Ocean
    The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

     has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November. In the Southern Hemisphere
    Southern Hemisphere
    The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

    , the tropical cyclone year begins on July 1 and runs all year-round and encompasses the tropical cyclone seasons, which run from November 1 until the end of April, with peaks in mid-February to early March.

    Season lengths and seasonal averages
    Basin Season start Season end Tropical Storms
    (>34 knots)
    Tropical Cyclones
    (>63 knots)
    Category 3+ TCs
    (>95 knots)
    Northwest Pacific April January 26.7 16.9 8.5
    South Indian November April 20.6 10.3 4.3
    Northeast Pacific May November 16.3 9.0 4.1
    North Atlantic June November 10.6 5.9 2.0
    Australia Southwest Pacific November April 9 4.8 1.9
    North Indian April December 5.4 2.2 0.4


    Factors


    The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood. While six factors appear to be generally necessary, tropical cyclones may occasionally form without meeting all of the following conditions. In most situations, water temperatures
    Sea surface temperature
    Sea surface temperature is the water temperature close to the oceans surface. The exact meaning of surface varies according to the measurement method used, but it is between and below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a...

     of at least 26.5 °C (79.7 °F) are needed down to a depth of at least 50 m (164 ft); waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms. Another factor is rapid cooling with height, which allows the release of the heat of condensation that powers a tropical cyclone. High humidity is needed, especially in the lower-to-mid troposphere
    Troposphere
    The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

    ; when there is a great deal of moisture in the atmosphere, conditions are more favorable for disturbances to develop. Low amounts of wind shear
    Wind shear
    Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...

     are needed, as high shear is disruptive to the storm's circulation. Tropical cyclones generally need to form more than 555 km (344.9 mi) or 5 degrees of latitude
    Latitude
    In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

     away from the equator
    Equator
    An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

    , allowing the Coriolis effect
    Coriolis effect
    In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

     to deflect winds blowing towards the low pressure center and creating a circulation. Lastly, a formative tropical cyclone needs a pre-existing system of disturbed weather, although without a circulation no cyclonic development will take place. Low-latitude and low-level westerly wind bursts associated with the Madden-Julian oscillation
    Madden-Julian oscillation
    The Madden–Julian oscillation ' is the largest element of the intraseasonal variability in the tropical atmosphere. It is a large-scale coupling between atmospheric circulation and tropical deep convection...

     can create favorable conditions for tropical cyclogenesis by initiating tropical disturbances.

    Locations


    Most tropical cyclones form in a worldwide band of thunderstorm activity called by several names: the Intertropical Front (ITF), the Intertropical Convergence Zone
    Intertropical Convergence Zone
    The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....

     (ITCZ), or the monsoon trough
    Monsoon trough
    The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...

    . Another important source of atmospheric instability is found in tropical wave
    Tropical wave
    Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which move from east to west across the tropics causing areas of...

    s, which cause about 85% of intense tropical cyclones in the Atlantic ocean, and become most of the tropical cyclones in the Eastern Pacific basin.

    Tropical cyclones move westward when equatorward of the subtropical ridge
    Subtropical ridge
    The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

    , intensifying as they move. Most of these systems form between 10 and 30 degrees away of the equator
    Equator
    An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

    , and 87% form no farther away than 20 degrees of latitude, north or south. Because the Coriolis effect
    Coriolis effect
    In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

     initiates and maintains tropical cyclone rotation, tropical cyclones rarely form or move within about 5 degrees of the equator, where the Coriolis effect is weakest. However, it is possible for tropical cyclones to form within this boundary as Tropical Storm Vamei
    Tropical Storm Vamei
    Tropical Storm Vamei was a Pacific tropical cyclone that formed closer to the equator than any other tropical cyclone worldwide...

     did in 2001 and Cyclone Agni
    Cyclone Agni
    Severe Cyclonic Storm Agni was a tropical cyclone of the 2004 North Indian Ocean cyclone season notable for its record proximity to the equator. It was the second North Indian Ocean cyclone to receive a name, after Onil earlier in the year...

     in 2004.

    Steering winds


    {{See also|Prevailing winds}}
    Although tropical cyclones are large systems generating enormous energy, their movements over the Earth's surface are controlled by large-scale winds—the streams in the Earth's atmosphere. The path of motion is referred to as a tropical cyclone's track and has been compared by Dr. Neil Frank, former director of the National Hurricane Center
    National Hurricane Center
    The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...

    , to "leaves carried along by a stream".

    Tropical systems, while generally located equator
    Equator
    An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

    ward of the 20th parallel, are steered primarily westward by the east-to-west winds on the equatorward side of the subtropical ridge
    Subtropical ridge
    The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

    —a persistent high-pressure area over the world's oceans. In the tropical North Atlantic and Northeast Pacific oceans, trade winds—another name for the westward-moving wind currents—steer tropical waves westward from the African coast and towards the Caribbean Sea, North America, and ultimately into the central Pacific ocean before the waves dampen out. These waves are the precursors to many tropical cyclones within this region. In the Indian Ocean
    Indian Ocean
    The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

     and Western Pacific (both north and south of the equator), tropical cyclogenesis is strongly influenced by the seasonal movement of the Intertropical Convergence Zone
    Intertropical Convergence Zone
    The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....

     and the monsoon trough
    Monsoon trough
    The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...

    , rather than by easterly waves. Tropical cyclones can also be steered by other systems, such as other low pressure systems, high pressure systems, warm front
    Warm front
    A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient...

    s, and cold front
    Cold front
    A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...

    s.

    Coriolis effect



    The Earth's rotation imparts an acceleration known as the Coriolis effect, Coriolis acceleration, or colloquially, Coriolis force. This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents. The poleward portion of a tropical cyclone contains easterly winds, and the Coriolis effect pulls them slightly more poleward. The westerly winds on the equatorward portion of the cyclone pull slightly towards the equator, but, because the Coriolis effect weakens toward the equator, the net drag on the cyclone is poleward. Thus, tropical cyclones in the Northern Hemisphere usually turn north (before being blown east), and tropical cyclones in the Southern Hemisphere usually turn south (before being blown east) when no other effects counteract the Coriolis effect.

    The Coriolis effect also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds – that force is the heat of condensation.

    Interaction with the mid-latitude westerlies


    {{See also|Westerlies}}

    When a tropical cyclone crosses the subtropical ridge
    Subtropical ridge
    The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

     axis, its general track around the high-pressure area is deflected significantly by winds moving towards the general low-pressure area to its north. When the cyclone track becomes strongly poleward with an easterly component, the cyclone has begun recurvature. A typhoon moving through the Pacific Ocean towards Asia, for example, will recurve offshore of Japan to the north, and then to the northeast, if the typhoon encounters southwesterly winds (blowing northeastward) around a low-pressure system passing over China or Siberia
    Siberia
    Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...

    . Many tropical cyclones are eventually forced toward the northeast by extratropical cyclone
    Extratropical cyclone
    Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

    s in this manner, which move from west to east to the north of the subtropical ridge. An example of a tropical cyclone in recurvature was Typhoon Ioke
    Hurricane Ioke
    Hurricane Ioke was the strongest hurricane ever recorded in the Central Pacific...

     in 2006, which took a similar trajectory.

    Landfall


    {{See also|List of notable tropical cyclones|Tropical cyclogenesis#Unusual areas of formation|l2=Unusual areas of tropical cyclone formation}}
    Officially, landfall
    Landfall (meteorology)
    Landfall is the event of a tropical cyclone or a waterspout coming onto land after being over water. When a waterspout makes landfall it is reclassified as a tornado, which can then cause damage inland...

    is when a storm's center (the center of its circulation, not its edge) crosses the coastline. Storm conditions may be experienced on the coast and inland hours before landfall; in fact, a tropical cyclone can launch its strongest winds over land, yet not make landfall; if this occurs, then it is said that the storm made a direct hit on the coast. As a result of the narrowness of this definition, the landfall area experiences half of a land-bound storm by the time the actual landfall occurs. For emergency preparedness, actions should be timed from when a certain wind speed or intensity of rainfall will reach land, not from when landfall will occur.

    Multiple storm interaction


    {{Main|Fujiwhara effect}}
    When two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. This phenomenon is called the Fujiwhara effect, after Sakuhei Fujiwhara
    Sakuhei Fujiwhara
    was a Japanese meteorologist who became the namesake for the Fujiwhara effect. Novelist Jirō Nitta is his nephew and mathematician Masahiko Fujiwara is his grandnephew.-Early life:...

    .

    Factors



    A tropical cyclone can cease to have tropical characteristics in several different ways. One such way is if it moves over land, thus depriving it of the warm water it needs to power itself, quickly losing strength. Most strong storms lose their strength very rapidly after landfall and become disorganized areas of low pressure within a day or two, or evolve into extratropical cyclone
    Extratropical cyclone
    Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

    s. There is a chance a tropical cyclone could regenerate if it managed to get back over open warm water, such as with Hurricane Ivan
    Hurricane Ivan
    Hurricane Ivan was a large, long-lived, Cape Verde-type hurricane that caused widespread damage in the Caribbean and United States. The cyclone was the ninth named storm, the sixth hurricane and the fourth major hurricane of the active 2004 Atlantic hurricane season...

    . If it remains over mountains for even a short time, weakening will accelerate. Many storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall, leading to deadly flood
    Flood
    A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

    s and mudslides, similar to those that happened with Hurricane Mitch
    Hurricane Mitch
    Hurricane Mitch was the most powerful hurricane and the most destructive of the 1998 Atlantic hurricane season, with maximum sustained winds of 180 mph . The storm was the thirteenth tropical storm, ninth hurricane, and third major hurricane of the season. Along with Hurricane Georges, Mitch...

     in 1998. In addition, dissipation can occur if a storm remains in the same area of ocean for too long, mixing the upper 60 metres (196.9 ft) of water, dropping sea surface temperatures more than 5 °C (9 °F). Without warm surface water, the storm cannot survive.

    A tropical cyclone can dissipate when it moves over waters significantly below 26.5 °C (79.7 °F). This will cause the storm to lose its tropical characteristics (i.e. thunderstorms near the center and warm core) and become a remnant low pressure area, which can persist for several days. This is the main dissipation mechanism in the Northeast Pacific ocean. Weakening or dissipation can occur if it experiences vertical wind shear
    Wind shear
    Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...

    , causing the convection and heat engine to move away from the center; this normally ceases development of a tropical cyclone. In addition, its interaction with the main belt of the Westerlies, by means of merging with a nearby frontal zone, can cause tropical cyclones to evolve into extratropical cyclones. This transition can take 1–3 days. Even after a tropical cyclone is said to be extratropical or dissipated, it can still have tropical storm force (or occasionally hurricane/typhoon force) winds and drop several inches of rainfall. In the Pacific ocean
    Pacific Ocean
    The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

     and Atlantic ocean
    Atlantic Ocean
    The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

    , such tropical-derived cyclones of higher latitudes can be violent and may occasionally remain at hurricane or typhoon-force wind speeds when they reach the west coast of North America. These phenomena can also affect Europe, where they are known as European windstorm
    European windstorm
    A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

    s
    ; Hurricane Iris's
    Hurricane Iris (1995)
    Hurricane Iris was the ninth named tropical cyclone and fifth hurricane of an active 1995 Atlantic hurricane season. Iris was one of four storms to form nearly simultaneously in the Atlantic during the 1995 season. Forming on August 22, Iris slowly drifted across the Leeward Islands as a tropical...

     extratropical remnants are an example of such a windstorm from 1995. In addition, a cyclone can merge with another area of low pressure, becoming a larger area of low pressure. This can strengthen the resultant system, although it may no longer be a tropical cyclone. Studies in the 2000s have given rise to the hypothesis that large amounts of dust reduce the strength of tropical cyclones.

    Artificial dissipation


    In the 1960s and 1970s, the United States government attempted to weaken hurricanes through Project Stormfury
    Project Stormfury
    Project Stormfury was an attempt to weaken tropical cyclones by flying aircraft into them and seeding with silver iodide. The project was run by the United States Government from 1962 to 1983....

     by seeding
    Cloud seeding
    Cloud seeding, a form of intentional weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud...

     selected storms with silver iodide
    Silver iodide
    Silver iodide is a yellow, inorganic, photosensitive iodide of silver used in photography, in medicine as an antiseptic, and in rainmaking for cloud seeding.-Crystal structure:...

    . It was thought that the seeding would cause supercooled water in the outer rainbands to freeze, causing the inner eyewall to collapse and thus reducing the winds. The winds of Hurricane Debbie
    Hurricane Debbie (1969)
    Hurricane Debbie was an intense and long-lived hurricane that formed during August 1969. The fifth tropical cyclone, fourth named storm, third hurricane and second major hurricane of the 1969 Atlantic hurricane season, Debbie formed on August 14 in the southern Atlantic Ocean and took a general...

    —a hurricane seeded in Project Stormfury—dropped as much as 31%, but Debbie regained its strength after each of two seeding forays. In an earlier episode in 1947, disaster struck when a hurricane east of Jacksonville, Florida
    Jacksonville, Florida
    Jacksonville is the largest city in the U.S. state of Florida in terms of both population and land area, and the largest city by area in the contiguous United States. It is the county seat of Duval County, with which the city government consolidated in 1968...

     promptly changed its course after being seeded, and smashed into Savannah, Georgia
    Savannah, Georgia
    Savannah is the largest city and the county seat of Chatham County, in the U.S. state of Georgia. Established in 1733, the city of Savannah was the colonial capital of the Province of Georgia and later the first state capital of Georgia. Today Savannah is an industrial center and an important...

    . Because there was so much uncertainty about the behavior of these storms, the federal government would not approve seeding operations unless the hurricane had a less than 10% chance of making landfall within 48 hours, greatly reducing the number of possible test storms. The project was dropped after it was discovered that eyewall replacement cycles occur naturally in strong hurricanes, casting doubt on the result of the earlier attempts. Today, it is known that silver iodide seeding is not likely to have an effect because the amount of supercooled water in the rainbands of a tropical cyclone is too low.

    Other approaches have been suggested over time, including cooling the water under a tropical cyclone by towing iceberg
    Iceberg
    An iceberg is a large piece of ice from freshwater that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice...

    s into the tropical oceans. Other ideas range from covering the ocean in a substance that inhibits evaporation, dropping large quantities of ice into the eye at very early stages of development (so that the latent heat is absorbed by the ice, instead of being converted to kinetic energy that would feed the positive feedback loop), or blasting the cyclone apart with nuclear weapons. Project Cirrus even involved throwing dry ice on a cyclone. These approaches all suffer from one flaw above many others: tropical cyclones are simply too large and short-lived for any of the weakening techniques to be practical.

    Effects



    {{Main|Effects of tropical cyclones}}
    Tropical cyclones out at sea cause large waves, heavy rain, and high winds, disrupting international shipping and, at times, causing shipwrecks. Tropical cyclones stir up water, leaving a cool wake behind them, which causes the region to be less favorable for subsequent tropical cyclones. On land, strong wind
    Wind
    Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...

    s can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. The storm surge
    Storm surge
    A storm surge is an offshore rise of water associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea...

    , or the increase in sea level due to the cyclone, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths.
    The broad rotation of a landfalling tropical cyclone, and vertical wind shear at its periphery, spawns tornadoes
    History of tropical cyclone-spawned tornadoes
    Intense tropical cyclones usually produce tornadoes, the majority of them weak, especially upon landfall.- List of Atlantic tropical cyclones which spawned tornadoes :These are the Atlantic tropical cyclones that are known to have spawned tornadoes in the U.S....

    . Tornadoes can also be spawned as a result of eyewall mesovortices, which persist until landfall.

    Over the past two centuries, tropical cyclones have been responsible for the deaths of about 1.9 million people worldwide. Large areas of standing water caused by flooding lead to infection, as well as contributing to mosquito-borne illnesses. Crowded evacuees in shelters
    Emergency shelter
    Emergency shelters are places for people to live temporarily when they can't live in their previous residence, similar to homeless shelters. The main difference is that an emergency shelter typically specializes in people fleeing a specific type of situation, such as natural or man-made disasters,...

     increase the risk of disease propagation. Tropical cyclones significantly interrupt infrastructure, leading to power outages, bridge destruction, and the hampering of reconstruction efforts.

    Although cyclones take an enormous toll in lives and personal property, they may be important factors in the precipitation
    Precipitation (meteorology)
    In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...

     regimes of places they impact, as they may bring much-needed precipitation to otherwise dry regions. Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes
    Middle latitudes
    The middle latitudes are between 23°26'22" North and 66°33'39" North, and between 23°26'22" South and 66°33'39" South latitude, or, the Earth's temperate zones between the tropics and the Arctic and Antarctic. The prevailing winds in the middle latitudes are often very strong...

     and polar regions, and by regulating the thermohaline circulation
    Thermohaline circulation
    The term thermohaline circulation refers to a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....

     through upwelling
    Upwelling
    Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...

    . The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal estuaries
    Estuary
    An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

    , which are typically important fish breeding locales. Tropical cyclone destruction spurs redevelopment, greatly increasing local property values.

    Observation


    {{Main|Tropical cyclone observation}}

    Intense tropical cyclones pose a particular observation challenge, as they are a dangerous oceanic phenomenon, and weather station
    Weather station
    A weather station is a facility, either on land or sea, with instruments and equipment for observing atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include temperature, barometric pressure, humidity, wind speed, wind...

    s, being relatively sparse, are rarely available on the site of the storm itself. In general, surface observations are available only if the storm is passing over an island or a coastal area, or if there is a nearby ship. Real-time measurements are usually taken in the periphery of the cyclone, where conditions are less catastrophic and its true strength cannot be evaluated. For this reason, there are teams of meteorologists that move into the path of tropical cyclones to help evaluate their strength at the point of landfall.

    Tropical cyclones far from land are tracked by weather satellite
    Weather satellite
    The weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while...

    s capturing visible and infrared
    Infrared
    Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

     images from space, usually at half-hour to quarter-hour intervals. As a storm approaches land, it can be observed by land-based Doppler
    Pulse-doppler radar
    Pulse-Doppler is a 4D radar system capable of detecting both target 3D location as well as measuring radial velocity . It uses the Doppler effect to avoid overloading computers and operators as well as to reduce power consumption...

     radar
    Weather radar
    Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...

    . Radar plays a crucial role around landfall by showing a storm's location and intensity every several minutes.

    In situ
    In situ
    In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may...

     measurements, in real-time, can be taken by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by United States government hurricane hunters
    Hurricane Hunters
    The Hurricane Hunters are aircraft that fly into tropical cyclones in the North Atlantic Ocean and Northeastern Pacific Ocean for the specific purpose of directly measuring weather data in and around those storms. In the United States, the Air Force, Navy, and NOAA units have all participated in...

    . The aircraft used are WC-130 Hercules and WP-3D Orions, both four-engine turboprop
    Turboprop
    A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...

     cargo aircraft. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft also launch GPS dropsondes inside the cyclone. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface. A new era in hurricane observation began when a remotely piloted Aerosonde
    Insitu Aerosonde
    The Aerosonde is a small unmanned aerial vehicle designed to collect weather data, including temperature, atmospheric pressure, humidity, and wind measurements, over oceans and remote areas. The Aerosonde was developed by Insitu, and is now manufactured by Aerosonde Ltd, which is a strategic...

    , a small drone aircraft, was flown through Tropical Storm Ophelia as it passed Virginia's Eastern Shore during the 2005 hurricane season. A similar mission was also completed successfully in the western Pacific ocean. This demonstrated a new way to probe the storms at low altitudes that human pilots seldom dare.


    Forecasting


    {{See also|Tropical cyclone track forecasting|Tropical cyclone prediction model|Tropical cyclone rainfall forecasting}}
    Because of the forces that affect tropical cyclone tracks, accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will change during the life of a tropical system. The deep layer mean flow, or average wind through the depth of the troposphere
    Troposphere
    The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

    , is considered the best tool in determining track direction and speed. If storms are significantly sheared, use of wind speed measurements at a lower altitude, such as at the 700 hPa pressure surface (3000 metres (9,842.5 ft) above sea level) will produce better predictions. Tropical forecasters also consider smoothing out short-term wobbles of the storm as it allows them to determine a more accurate long-term trajectory. High-speed computers and sophisticated simulation software allow forecasters to produce computer models
    Tropical cyclone prediction model
    A tropical cyclone forecast model is a computer program that uses meteorological data to forecast aspects of the future state of tropical cyclones. There are three types of models: statistical, dynamical, or combined statistical-dynamic...

     that predict tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. Combining forecast models with increased understanding of the forces that act on tropical cyclones, as well as with a wealth of data from Earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades. However, scientists are not as skillful at predicting the intensity of tropical cyclones. The lack of improvement in intensity forecasting is attributed to the complexity of tropical systems and an incomplete understanding of factors that affect their development.

    Intensity classifications


    {{Main|Tropical cyclone scales}}

    Tropical cyclones are classified into three main groups, based on intensity: tropical depressions, tropical storms, and a third group of more intense storms, whose name depends on the region. For example, if a tropical storm in the Northwestern Pacific reaches hurricane-strength winds on the Beaufort scale
    Beaufort scale
    The Beaufort Scale is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the Beaufort Wind Force Scale.-History:...

    , it is referred to as a typhoon; if a tropical storm passes the same benchmark in the Northeast Pacific Basin
    Pacific hurricane
    A Pacific hurricane or tropical storm is a tropical cyclone that develops in the northeastern part of the Pacific Ocean. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, , central , and western...

    , or in the Atlantic
    Atlantic hurricane
    North Atlantic tropical cyclones usually form in the northern hemisphere summer or fall. Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph , while hurricanes have one-minute maximum sustained exceeding 74 mph...

    , it is called a hurricane. Neither "hurricane" nor "typhoon" is used in either the Southern Hemisphere or the Indian Ocean. In these basins
    Tropical cyclone basins
    Traditionally, areas of tropical cyclone formation are divided into seven basins. These include the north Atlantic Ocean, the eastern and western parts of the northern Pacific Ocean, the southwestern Pacific, the southwestern and southeastern Indian Oceans, and the northern Indian Ocean. The...

    , storms of tropical nature are referred to simply as "cyclones".

    As indicated in the table below, each basin uses a separate system of terminology
    Tropical cyclone scales
    Tropical systems are officially ranked on one of several tropical cyclone scales according to their maximum sustained winds and in what oceanic basin they are located...

    , making comparisons between different basins difficult. In the Pacific Ocean, hurricanes from the Central North Pacific sometimes cross the International Date Line
    International Date Line
    The International Date Line is a generally north-south imaginary line on the surface of the Earth, passing through the middle of the Pacific Ocean, that designates the place where each calendar day begins...

     into the Northwest Pacific, becoming typhoons (such as Hurricane/Typhoon Ioke
    Hurricane Ioke
    Hurricane Ioke was the strongest hurricane ever recorded in the Central Pacific...

     in 2006); on rare occasions, the reverse will occur. It should also be noted that typhoons with sustained winds greater than 67 metres per second (123.1 kn) or 150 miles per hour (241.4 km/h) are called Super Typhoons by the Joint Typhoon Warning Center.

    Tropical depression


    A tropical depression is an organized system of clouds and thunderstorms with a defined, closed surface circulation and maximum sustained wind
    Maximum sustained wind
    The maximum sustained winds associated with a tropical cyclone are a common indicator of the intensity of the storm. Within a mature tropical cyclone, they are found within the eyewall at a distance defined as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are...

    s of less than 17 metres per second (31.2 kn) or 38 miles per hour (61.2 km/h). It has no eye
    Eye (cyclone)
    The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...

     and does not typically have the organization or the spiral shape of more powerful storms. However, it is already a low-pressure system, hence the name "depression". The practice of the Philippines
    Philippines
    The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

     is to name tropical depressions from their own naming convention when the depressions are within the Philippines' area of responsibility.

    Tropical storm


    A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 17 metres per second (31.2 kn) (39 miles per hour (62.8 km/h)) and 32 metres per second (58.8 kn) (73 miles per hour (117.5 km/h)). At this point, the distinctive cyclonic shape starts to develop, although an eye is not usually present. Government weather services, other than the Philippines, first assign names to systems that reach this intensity (thus the term named storm).

    Hurricane or typhoon


    A hurricane or typhoon (sometimes simply referred to as a tropical cyclone, as opposed to a depression or storm) is a system with sustained winds of at least 33 metres per second (60.6 kn) or 74 miles per hour (119.1 km/h). A cyclone of this intensity tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of circulation. The eye is often visible in satellite images as a small, circular, cloud-free spot. Surrounding the eye is the eyewall, an area about 16 kilometres (9.9 mi) to 80 kilometres (49.7 mi) wide in which the strongest thunderstorm
    Thunderstorm
    A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...

    s and winds circulate around the storm's center. Maximum sustained winds in the strongest tropical cyclones have been estimated at about 85 metres per second (156.1 kn) or 195 miles per hour (313.8 km/h).
    {{Tropical cyclone classification}}

    Origin of storm terms


    The word typhoon, which is used today in the Northwest Pacific, may be derived from Hindi/Urdu, Persian
    Persian language
    Persian is an Iranian language within the Indo-Iranian branch of the Indo-European languages. It is primarily spoken in Iran, Afghanistan, Tajikistan and countries which historically came under Persian influence...

     and Arabic
    Arabic language
    Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

     ţūfān (طوفان), which in turn originates from Greek
    Greek language
    Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

     Typhon
    Typhon
    Typhon , also Typhoeus , Typhaon or Typhos was the last son of Gaia, fathered by Tartarus, and the most deadly monster of Greek mythology. He was known as the "Father of all monsters"; his wife Echidna was likewise the "Mother of All Monsters."Typhon was described in pseudo-Apollodorus,...

    (Τυφών), a monster from Greek mythology
    Greek mythology
    Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

     associated with storms. The related Portuguese
    Portuguese language
    Portuguese is a Romance language that arose in the medieval Kingdom of Galicia, nowadays Galicia and Northern Portugal. The southern part of the Kingdom of Galicia became independent as the County of Portugal in 1095...

     word tufão, used in Portuguese for typhoons, is also derived from Typhon. The word is also similar to Chinese "taifeng" ("toifung" in Cantonese
    Cantonese
    Cantonese is a dialect spoken primarily in south China.Cantonese may also refer to:* Yue Chinese, the Chinese language that includes Cantonese* Cantonese cuisine, the cuisine of Guangdong province...

    ) (颱風 – great winds), and also to the Japanese "taifu" (台風), which may explain why "typhoon" came to be used for East Asian cyclones.{{Citation needed|date=August 2009|reason=Sounds like a folk etymology.}}

    The word hurricane, used in the North Atlantic and Northeast Pacific, is derived from huracán, the Spanish word for the Carib/Taino
    Taíno people
    The Taínos were pre-Columbian inhabitants of the Bahamas, Greater Antilles, and the northern Lesser Antilles. It is thought that the seafaring Taínos are relatives of the Arawak people of South America...

     storm god, Juracán
    Juracán
    Juracán is the phonetic name given by the Spanish settlers to the god of chaos and disorder that the Taino Indians in Puerto Rico believed controlled the weather, particularly hurricanes. From this we derive the Spanish word huracán and eventually the English word hurricane...

    . This god is believed by scholars to have been at least partially derived from the Mayan
    Maya peoples
    The Maya people constitute a diverse range of the Native American people of southern Mexico and northern Central America. The overarching term "Maya" is a collective designation to include the peoples of the region who share some degree of cultural and linguistic heritage; however, the term...

     creator god, Huracan
    Huracan
    Huracan , in Mayan understandable as Jun Raqan "one legged", is a K'iche' Mayan god of wind, storm, fire and one of the creator deities who participated in all three attempts at creating humanity...

    . Huracan was believed by the Mayans to have created dry land out of the turbulent waters. The god was also credited with later destroying the "wooden people", the precursors to the "maize people
    Maya maize god
    Like other Mesoamerican peoples, the traditional Mayas recognize in their staple crop, the maize, a vital force with which they strongly identify. This is clearly shown by their mythological traditions. According to the 16th-century Popol Vuh, the Hero Twins have maize plants for alter egos and man...

    ", with an immense storm and flood. Huracan is also the source of the word orcan, another word for a particularly strong European windstorm
    European windstorm
    A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

    .

    Naming


    {{Main|Tropical cyclone naming|Lists of tropical cyclone names}}
    Storms reaching tropical storm strength were initially given names to eliminate confusion when there are multiple systems in any individual basin at the same time, which assists in warning people of the coming storm. In most cases, a tropical cyclone retains its name throughout its life; however, under special circumstances, tropical cyclones may be renamed while active. These names are taken from lists that vary from region to region and are usually drafted a few years ahead of time. The lists are decided on, depending on the regions, either by committees of the World Meteorological Organization
    World Meteorological Organization
    The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

     (called primarily to discuss many other issues) or by national weather offices involved in the forecasting of the storms. Each year, the names of particularly destructive storms (if there are any) are "retired" and new names are chosen to take their place. Different countries have different local conventions; for example, in Japan, storms are referred to by number (each year), such as 台風第9号 (Typhoon #9).

    Notable tropical cyclones


    {{Main|List of notable tropical cyclones|List of Atlantic hurricanes|List of Pacific hurricanes}}
    Tropical cyclones that cause extreme destruction are rare, although when they occur, they can cause great amounts of damage or thousands of fatalities.
    The 1970 Bhola cyclone
    1970 Bhola cyclone
    The 1970 Bhola cyclone was a devastating tropical cyclone that struck East Pakistan and India's West Bengal on November 12, 1970. It was the deadliest tropical cyclone ever recorded, and one of the deadliest natural disasters in modern times...

     is the deadliest tropical cyclone on record, killing more than 300,000 people and potentially as many as 1 million after striking the densely populated Ganges Delta
    Ganges Delta
    The Ganges Delta is a river delta in the South Asia region of Bengal, consisting of Bangladesh and the state of West Bengal, India. It is the world's largest delta, and empties into the Bay of Bengal...

     region of Bangladesh
    Bangladesh
    Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...

     on 13 November 1970. Its powerful storm surge was responsible for the high death toll. The North Indian cyclone basin has historically been the deadliest basin. Elsewhere, Typhoon Nina
    Typhoon Nina (1975)
    Super Typhoon Nina was a short-lived but intense super typhoon that caused catastrophic damage and loss of life in China after causing the Banqiao Dam to collapse...

     killed nearly 100,000 in China in 1975 due to a 100-year flood
    100-year flood
    A one-hundred-year flood is calculated to be the level of flood water expected to be equaled or exceeded every 100 years on average. The 100-year flood is more accurately referred to as the 1% annual exceedance probability flood, since it is a flood that has a 1% chance of being equaled or exceeded...

     that caused 62 dams including the Banqiao Dam
    Banqiao Dam
    The Banqiao Reservoir Dam is a dam on the River Ru in Zhumadian Prefecture, Henan province, China. It infamously failed in 1975, causing more casualties than any other dam failure in history, and was subsequently rebuilt....

     to fail. The Great Hurricane of 1780
    Great Hurricane of 1780
    The Great Hurricane of 1780, also known as Hurricane San Calixto, the Great Hurricane of the Antilles, and the 1780 Disaster, is the deadliest Atlantic hurricane on record. Over 20,000 people died when the storm passed through the Lesser Antilles in the Caribbean between October 10 and October...

     is the deadliest Atlantic hurricane
    Atlantic hurricane
    North Atlantic tropical cyclones usually form in the northern hemisphere summer or fall. Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph , while hurricanes have one-minute maximum sustained exceeding 74 mph...

     on record, killing about 22,000 people in the Lesser Antilles
    Lesser Antilles
    The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...

    . A tropical cyclone does need not be particularly strong to cause memorable damage, primarily if the deaths are from rainfall or mudslides. Tropical Storm Thelma
    Tropical Storm Thelma
    Tropical Storm Thelma was the deadliest tropical storm of the 1991 Pacific typhoon season, killing between 5,101 to 8,100 people as it crossed the Philippines.-Meteorological history:A tropical disturbance developed over the eastern Caroline Islands in late October...

     in November 1991 killed thousands in the Philippines
    Philippines
    The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

    , while in 1982, the unnamed tropical depression that eventually became Hurricane Paul killed around 1,000 people in Central America
    Central America
    Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

    .

    Hurricane Katrina
    Hurricane Katrina
    Hurricane Katrina of the 2005 Atlantic hurricane season was a powerful Atlantic hurricane. It is the costliest natural disaster, as well as one of the five deadliest hurricanes, in the history of the United States. Among recorded Atlantic hurricanes, it was the sixth strongest overall...

     is estimated as the costliest tropical cyclone worldwide, causing $81.2 billion in property damage (2008 USD) with overall damage estimates exceeding $100 billion (2005 USD). Katrina killed at least 1,836 people after striking Louisiana
    Louisiana
    Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

     and Mississippi
    Mississippi
    Mississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...

     as a major hurricane
    Tropical cyclone scales
    Tropical systems are officially ranked on one of several tropical cyclone scales according to their maximum sustained winds and in what oceanic basin they are located...

     in August 2005. Hurricane Andrew
    Hurricane Andrew
    Hurricane Andrew was the third Category 5 hurricane to make landfall in the United States, after the Labor Day Hurricane of 1935 and Hurricane Camille in 1969. Andrew was the first named storm and only major hurricane of the otherwise inactive 1992 Atlantic hurricane season...

     is the second most destructive tropical cyclone in U.S history, with damages totaling $40.7 billion (2008 USD), and with damage costs at $31.5 billion (2008 USD), Hurricane Ike
    Hurricane Ike
    Hurricane Ike was the second-costliest hurricane ever to make landfall in the United States, the costliest hurricane ever to impact Cuba and the second most active hurricane to reach the Canadian mainland in the Great Lakes Region after Hurricane Hazel in 1954...

     is the third most destructive tropical cyclone in U.S history. The Galveston Hurricane of 1900
    Galveston Hurricane of 1900
    The Hurricane of 1900 made landfall on the city of Galveston in the U.S. state of Texas, on September 8, 1900.It had estimated winds of at landfall, making it a Category 4 storm on the Saffir-Simpson Hurricane Scale...

     is the deadliest natural disaster in the United States, killing an estimated 6,000 to 12,000 people in Galveston, Texas
    Galveston, Texas
    Galveston is a coastal city located on Galveston Island in the U.S. state of Texas. , the city had a total population of 47,743 within an area of...

    . Hurricane Mitch
    Hurricane Mitch
    Hurricane Mitch was the most powerful hurricane and the most destructive of the 1998 Atlantic hurricane season, with maximum sustained winds of 180 mph . The storm was the thirteenth tropical storm, ninth hurricane, and third major hurricane of the season. Along with Hurricane Georges, Mitch...

     caused more than 10,000 fatalities in Latin America. Hurricane Iniki
    Hurricane Iniki
    Hurricane Iniki was the most powerful hurricane to strike the U.S. state of Hawaii in recorded history. Forming on September 5 during the strong El Niño of 1991–1994, Iniki was one of eleven Central Pacific tropical cyclones during the 1992 season. It attained tropical storm status on...

     in 1992 was the most powerful storm to strike Hawaii
    Hawaii
    Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

     in recorded history, hitting Kauai
    Kauai
    Kauai or Kauai, known as Tauai in the ancient Kaua'i dialect, is geologically the oldest of the main Hawaiian Islands. With an area of , it is the fourth largest of the main islands in the Hawaiian archipelago, and the 21st largest island in the United States. Known also as the "Garden Isle",...

     as a Category 4 hurricane, killing six people, and causing U.S. $3 billion in damage. Kauai was also struck by Hurricanes Dot (1959) and Iwa (1982) (see List of Hawaii hurricanes). Other destructive Eastern Pacific hurricane
    Pacific hurricane
    A Pacific hurricane or tropical storm is a tropical cyclone that develops in the northeastern part of the Pacific Ocean. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, , central , and western...

    s include Pauline
    Hurricane Pauline
    Hurricane Pauline was one of the strongest and deadliest Pacific hurricanes to make landfall on Mexico. The sixteenth tropical storm, eighth hurricane, and seventh major hurricane of the 1997 Pacific hurricane season, Pauline developed out of a tropical wave on October 5 about 250 miles ...

     and Kenna
    Hurricane Kenna
    Hurricane Kenna was the second-most intense Pacific hurricane to strike the west coast of Mexico in recorded history. Kenna was the sixteenth tropical depression, thirteenth tropical storm, seventh hurricane, sixth major hurricane, and third Category 5 hurricane of the 2002 Pacific hurricane season...

    , both causing severe damage after striking Mexico
    Mexico
    The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

     as major hurricanes. In March 2004, Cyclone Gafilo
    Cyclone Gafilo
    Cyclone Gafilo was a powerful tropical cyclone which struck Madagascar in March 2004, causing devastating damage. It is the most intense cyclone ever to form in the south-western Indian Ocean.-Meteorological history:...

     struck northeastern Madagascar
    Madagascar
    The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

     as a powerful cyclone, killing 74, affecting more than 200,000, and becoming the worst cyclone to affect the nation for more than 20 years.


    The most intense storm on record was Typhoon Tip
    Typhoon Tip
    Typhoon Tip was the largest and most intense tropical cyclone on record. The nineteenth tropical storm and twelfth typhoon of the 1979 Pacific typhoon season, Tip developed out of a disturbance in the monsoon trough on October 4 near Pohnpei...

     in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870 mbar (652.5 mmHg) and maximum sustained wind speeds of 165 knots (89.8 m/s) or 190 miles per hour (305.8 km/h). Tip
    Typhoon Tip
    Typhoon Tip was the largest and most intense tropical cyclone on record. The nineteenth tropical storm and twelfth typhoon of the 1979 Pacific typhoon season, Tip developed out of a disturbance in the monsoon trough on October 4 near Pohnpei...

    , however, does not solely hold the record for fastest sustained winds in a cyclone. Typhoon Keith in the Pacific and Hurricanes Camille
    Hurricane Camille
    Hurricane Camille was the third and strongest tropical cyclone and second hurricane during the 1969 Atlantic hurricane season. The second of three catastrophic Category 5 hurricanes to make landfall in the United States during the 20th century , which it did near the mouth of the Mississippi River...

     and Allen
    Hurricane Allen
    Hurricane Allen was the first and strongest hurricane of the 1980 Atlantic hurricane season. It was one of the strongest hurricanes in recorded history, one of the few hurricanes to reach Category 5 status on the Saffir-Simpson Hurricane Scale on three separate occasions, and spent more time...

     in the North Atlantic currently share this record with Tip. Camille was the only storm to actually strike land while at that intensity, making it, with 165 knots (89.8 m/s) or 190 miles per hour (305.8 km/h) sustained winds and 183 knots (99.6 m/s) or 210 miles per hour (338 km/h) gusts, the strongest tropical cyclone on record at landfall. Typhoon Nancy
    Typhoon Nancy (1961)
    Super Typhoon Nancy was a powerful tropical cyclone of the 1961 Pacific typhoon season. The system with possibly the strongest winds ever measured in a tropical cyclone, Nancy caused extensive damage and at least 173 deaths and thousands of injuries in Japan and elsewhere in September 1961...

     in 1961 had recorded wind speeds of 185 knots (100.7 m/s) or 215 miles per hour (346 km/h), but recent research indicates that wind speeds from the 1940s to the 1960s were gauged too high, and this is no longer considered the storm with the highest wind speeds on record. Likewise, a surface-level gust caused by Typhoon Paka
    Typhoon Paka
    Typhoon Paka was the last tropical cyclone in the 1997 Pacific Ocean hurricane and typhoon season, and was among the strongest Pacific typhoons in the month of December. Paka, which is the Hawaiian name for Pat, developed on November 28 from a trough well to the southwest of Hawaii...

     on Guam
    Guam
    Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...

     was recorded at 205 knots (111.6 m/s) or 235 miles per hour (378.2 km/h). Had it been confirmed, it would be the strongest non-tornadic
    Tornado
    A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...

     wind ever recorded on the Earth's surface, but the reading had to be discarded since the anemometer
    Anemometer
    An anemometer is a device for measuring wind speed, and is a common weather station instrument. The term is derived from the Greek word anemos, meaning wind, and is used to describe any airspeed measurement instrument used in meteorology or aerodynamics...

     was damaged by the storm. Hurricane Wilma
    Hurricane Wilma
    Hurricane Wilma was the most intense tropical cyclone ever recorded in the Atlantic basin. Wilma was the twenty-second storm , thirteenth hurricane, sixth major hurricane, and fourth Category 5 hurricane of the record-breaking 2005 season...

     is the most intense tropical cyclone in the Atlantic Basin and the strongest tropical cyclone in the Western Hemisphere.

    In addition to being the most intense tropical cyclone on record, Tip was the largest cyclone on record, with tropical storm-force winds 2170 kilometres (1,348.4 mi) in diameter. The smallest storm on record, Tropical Storm Marco
    Tropical Storm Marco (2008)
    Tropical Storm Marco was the smallest known tropical cyclone on record. The thirteenth named storm of the 2008 Atlantic hurricane season, Marco developed out of a broad area of low pressure over the northwestern Caribbean during late September 2008. Influenced by a tropical wave on October 4,...

    , formed during October 2008, and made landfall in Veracruz
    Veracruz
    Veracruz, formally Veracruz de Ignacio de la Llave officially Estado Libre y Soberano de Veracruz de Ignacio de la Llave , is one of the 31 states that, along with the Federal District, comprise the 32 federative entities of Mexico. It is divided in 212 municipalities and its capital city is...

    . Marco generated tropical storm-force winds only 37 kilometres (23 mi) in diameter.

    Hurricane John
    Hurricane John (1994)
    Hurricane John formed during the 1994 Pacific hurricane season and became both the longest-lasting and the farthest-traveling tropical cyclone ever observed...

     is the longest-lasting tropical cyclone on record, lasting 31 days in 1994
    1994 Pacific hurricane season
    The 1994 Pacific hurricane season officially started on May 15, 1994 in the eastern Pacific, and on June 1, 1994 in the central Pacific, and lasted until November 30, 1994. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean...

    . Before the advent of satellite imagery in 1961, however, many tropical cyclones were underestimated in their durations. John is also the longest-tracked tropical cyclone in the Northern Hemisphere on record, which had a path of 7,165 miles (13,280 km). Reliable data for Southern Hemisphere cyclones is unavailable.

    Changes caused by El Niño-Southern Oscillation


    {{See also|El Niño-Southern Oscillation}}
    Most tropical cyclones form on the side of the subtropical ridge closer to the equator
    Equator
    An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

    , then move poleward past the ridge axis before recurving into the main belt of the Westerlies
    Westerlies
    The Westerlies, anti-trades, or Prevailing Westerlies, are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. These prevailing winds blow from the west to the east, and steer extratropical...

    . When the subtropical ridge
    Subtropical ridge
    The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

     position shifts due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan
    Japan
    Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

     and Korea
    Korea
    Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

     tend to experience much fewer September–November tropical cyclone impacts during El Niño and neutral years. During El Niño years, the break in the subtropical ridge tends to lie near 130°E
    130th meridian east
    The meridian 130° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, Australia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole....

     which would favor the Japanese archipelago. During El Niño years, Guam
    Guam
    Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...

    's chance of a tropical cyclone impact is one-third of the long term average. The tropical Atlantic ocean experiences depressed activity due to increased vertical wind shear
    Wind shear
    Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...

     across the region during El Niño years. During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific ocean, which increases the landfall threat to China
    China
    Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

    .

    Long-term activity trends

    {{See also|Atlantic hurricane reanalysis}}



    While the number of storms in the Atlantic has increased since 1995, there is no obvious global trend; the annual number of tropical cyclones worldwide remains about 87 ± 10 (Between 77 and 97 tropical cyclones annually). However, the ability of climatologists to make long-term data analysis in certain basins is limited by the lack of reliable historical data in some basins, primarily in the Southern Hemisphere. In spite of that, there is some evidence that the intensity of hurricanes is increasing. Kerry Emanuel
    Kerry Emanuel
    Kerry Emanuel is an American professor of meteorology currently working at the Massachusetts Institute of Technology in Cambridge. In particular he has specialized in atmospheric convection and the mechanisms acting to intensify hurricanes. He coined the term "hypercane" in 1994. In 2007, he was...

     stated, "Records of hurricane activity worldwide show an upswing of both the maximum wind speed in and the duration of hurricanes. The energy released by the average hurricane (again considering all hurricanes worldwide) seems to have increased by around 70% in the past 30 years or so, corresponding to about a 15% increase in the maximum wind speed and a 60% increase in storm lifetime."

    Atlantic storms are becoming more destructive financially, since five of the ten most expensive storms in United States history have occurred since 1990. According to the World Meteorological Organization
    World Meteorological Organization
    The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

    , “recent increase in societal impact from tropical cyclones has been caused largely by rising concentrations of population and infrastructure in coastal regions.” Pielke et al. (2008) normalized mainland U.S. hurricane damage from 1900–2005 to 2005 values and found no remaining trend of increasing absolute damage. The 1970s and 1980s were notable because of the extremely low amounts of damage compared to other decades. The decade 1996–2005 was the second most damaging among the past 11 decades, with only the decade 1926–1935 surpassing its costs. The most damaging single storm is the 1926 Miami hurricane
    1926 Miami Hurricane
    The 1926 Miami hurricane was a Category 4 hurricane that devastated Miami in September 1926. The storm also caused significant damage in the Florida Panhandle, the U.S. state of Alabama, and the Bahamas...

    , with $157 billion of normalized damage.

    Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast may have gone unmeasured in some instances. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect.

    The number and strength of Atlantic hurricanes may undergo a 50–70 year cycle, also known as the Atlantic Multidecadal Oscillation
    Atlantic Multidecadal Oscillation
    The Atlantic multidecadal oscillation is a mode of variability occurring in the North Atlantic Ocean and which has its principal expression in the sea surface temperature field...

    . Nyberg et al. reconstructed Atlantic major hurricane activity back to the early 18th century and found five periods averaging 3–5 major hurricanes per year and lasting 40–60 years, and six other averaging 1.5–2.5 major hurricanes per year and lasting 10–20 years. These periods are associated with the Atlantic multidecadal oscillation. Throughout, a decadal oscillation related to solar irradiance was responsible for enhancing/dampening the number of major hurricanes by 1–2 per year.

    Although more common since 1995, few above-normal hurricane seasons occurred during 1970–94. Destructive hurricanes struck frequently from 1926–60, including many major New England hurricanes. Twenty-one Atlantic tropical storms formed in 1933
    1933 Atlantic hurricane season
    The 1933 Atlantic hurricane season was the second most active Atlantic hurricane season on record, with 21 storms forming during that year in the northwest Atlantic Ocean. The season ran through the summer and the first half of fall in 1933, and was surpassed in total number of tropical cyclones by...

    , a record only recently exceeded in 2005
    2005 Atlantic hurricane season
    The 2005 Atlantic hurricane season was the most active Atlantic hurricane season in recorded history, repeatedly shattering numerous records. The impact of the season was widespread and ruinous with an estimated 3,913 deaths and record damage of about $159.2 billion...

    , which saw 28 storms. Tropical hurricanes occurred infrequently during the seasons of 1900–25; however, many intense storms formed during 1870–99. During the 1887 season
    1887 Atlantic hurricane season
    Another May storm formed south of Jamaica on May 17, way outside of the season and moved generally northward. It crossed Cuba on the 19th as a tropical storm, and moved out to sea. Two peaked at twice, once on May 18 and May 20. Two dissipated on the 21st in the Atlantic Ocean...

    , 19 tropical storms formed, of which a record 4 occurred after 1 November and 11 strengthened into hurricanes. Few hurricanes occurred in the 1840s to 1860s; however, many struck in the early 19th century, including a 1821 storm
    1821 Norfolk and Long Island Hurricane
    The 1821 Norfolk and Long Island Hurricane was one of four known tropical cyclones that have made landfall in New York City. Another, even more intense hurricane struck the region in pre-Columbian times and was detected by paleotempestological research...

     that made a direct hit on New York City
    New York City
    New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

    . Some historical weather experts say these storms may have been as high as Category 4
    Saffir-Simpson Hurricane Scale
    The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...

     in strength.

    These active hurricane seasons predated satellite coverage of the Atlantic basin. Before the satellite era began in 1960, tropical storms or hurricanes went undetected unless a reconnaissance aircraft encountered one, a ship reported a voyage through the storm, or a storm hit land in a populated area. The official record, therefore, could miss storms in which no ship experienced gale-force winds, recognized it as a tropical storm (as opposed to a high-latitude extra-tropical cyclone, a tropical wave, or a brief squall), returned to port, and reported the experience.

    Proxy records based on paleotempestological
    Paleotempestology
    Paleotempestology is the study of past tropical cyclone activity by means of geological proxies as well as historical documentary records. The term was coined by Kerry Emanuel.-Sedimentary proxy records:...

     research have revealed that major hurricane activity along the Gulf of Mexico
    Gulf of Mexico
    The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

     coast varies on timescales of centuries to millennia. Few major hurricanes struck the Gulf coast during 3000–1400 BC and again during the most recent millennium. These quiescent intervals were separated by a hyperactive period during 1400 BC and 1000 AD, when the Gulf coast was struck frequently by catastrophic hurricanes and their landfall probabilities increased by 3–5 times. This millennial-scale variability has been attributed to long-term shifts in the position of the Azores High
    Azores High
    The Azores High is a large subtropical semi-permanent centre of high atmospheric pressure found near the Azores in the Atlantic Ocean, at the Horse latitudes...

    , which may also be linked to changes in the strength of the North Atlantic Oscillation
    North Atlantic oscillation
    The North Atlantic oscillation is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through east-west oscillation motions of the Icelandic low and the Azores high, it controls the...

    .

    According to the Azores High hypothesis, an anti-phase pattern is expected to exist between the Gulf of Mexico coast and the Atlantic coast. During the quiescent periods, a more northeasterly position of the Azores High would result in more hurricanes being steered towards the Atlantic coast. During the hyperactive period, more hurricanes were steered towards the Gulf coast as the Azores High was shifted to a more southwesterly position near the Caribbean. Such a displacement of the Azores High is consistent with paleoclimatic evidence that shows an abrupt onset of a drier climate in Haiti
    Haiti
    Haiti , officially the Republic of Haiti , is a Caribbean country. It occupies the western, smaller portion of the island of Hispaniola, in the Greater Antillean archipelago, which it shares with the Dominican Republic. Ayiti was the indigenous Taíno or Amerindian name for the island...

     around 3200 14C
    Radiocarbon dating
    Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...

     years BP, and a change towards more humid conditions in the Great Plains
    Great Plains
    The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...

     during the late-Holocene as more moisture was pumped up the Mississippi Valley through the Gulf coast. Preliminary data from the northern Atlantic coast seem to support the Azores High hypothesis. A 3000-year proxy record from a coastal lake in Cape Cod
    Cape Cod
    Cape Cod, often referred to locally as simply the Cape, is a cape in the easternmost portion of the state of Massachusetts, in the Northeastern United States...

     suggests that hurricane activity increased significantly during the past 500–1000 years, just as the Gulf coast was amid a quiescent period of the last millennium.

    Global warming

    {{See also|Effects of global warming|Hurricane Katrina and global warming}}

    The U.S. National Oceanic and Atmospheric Administration
    National Oceanic and Atmospheric Administration
    The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

     Geophysical Fluid Dynamics Laboratory
    Geophysical Fluid Dynamics Laboratory
    The Geophysical Fluid Dynamics Laboratory is a laboratory in the National Oceanic and Atmospheric Administration /Office of Oceanic and Atmospheric Research . The current director is Dr. V...

     performed a simulation to determine if there is a statistical
    Statistics
    Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....

     trend
    Periodic trends
    In Chemistry, periodic trends are the tendencies of certain elemental characteristics to increase or decrease as one progresses along a row or column of the periodic table of elements.-Atomic radius:...

     in the frequency or strength of tropical cyclones over time. The simulation concluded "the strongest hurricanes in the present climate may be upstaged by even more intense hurricanes over the next century as the earth's climate is warmed by increasing levels of greenhouse gases in the atmosphere".

    In an article in Nature
    Nature (journal)
    Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

    , Kerry Emanuel
    Kerry Emanuel
    Kerry Emanuel is an American professor of meteorology currently working at the Massachusetts Institute of Technology in Cambridge. In particular he has specialized in atmospheric convection and the mechanisms acting to intensify hurricanes. He coined the term "hypercane" in 1994. In 2007, he was...

     stated that potential hurricane destructiveness, a measure combining hurricane strength, duration, and frequency, "is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multidecadal oscillations in the North Atlantic and North Pacific, and global warming". Emanuel predicted "a substantial increase in hurricane-related losses in the twenty-first century". In more recent work published by Emanuel (in the March 2008 issue of the Bulletin of the American Meteorological Society), he states that new climate modeling data indicates “global warming should reduce the global frequency of hurricanes.” According to the Houston Chronicle, the new work suggests that, even in a dramatically warming world, hurricane frequency and intensity may not substantially rise during the next two centuries.

    Likewise, P.J. Webster and others published an article in Science
    Science (journal)
    Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....

    examining the "changes in tropical cyclone number, duration, and intensity" over the past 35 years, the period when satellite data has been available. Their main finding was although the number of cyclones decreased throughout the planet excluding the north Atlantic Ocean
    Atlantic Ocean
    The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

    , there was a great increase in the number and proportion of very strong cyclones.

    {{Costliest U.S. Atlantic hurricanes by wealth normalization|align=right}}
    The strength of the reported effect is surprising in light of modeling studies that predict only a one-half category increase in storm intensity as a result of a ~2 °C (3.6 °F) global warming. Such a response would have predicted only a ~10% increase in Emanuel's potential destructiveness index during the 20th century rather than the ~75–120% increase he reported. Second, after adjusting for changes in population and inflation, and despite a more than 100% increase in Emanuel's potential destructiveness index, no statistically significant increase in the monetary damages resulting from Atlantic hurricanes has been found.

    Sufficiently warm sea surface temperatures are considered vital to the development of tropical cyclones. Although neither study can directly link hurricanes with global warming, the increase in sea surface temperatures is believed to be due to both global warming and natural variability, e.g. the hypothesized Atlantic Multidecadal Oscillation
    Atlantic Multidecadal Oscillation
    The Atlantic multidecadal oscillation is a mode of variability occurring in the North Atlantic Ocean and which has its principal expression in the sea surface temperature field...

     (AMO), although an exact attribution has not been defined. However, recent temperatures are the warmest ever observed for many ocean basins.

    In February 2007, the United Nations
    United Nations
    The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

     Intergovernmental Panel on Climate Change
    Intergovernmental Panel on Climate Change
    The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

     released its fourth assessment report
    IPCC Fourth Assessment Report
    Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for...

     on climate change
    Climate change
    Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

    . The report noted many observed changes in the climate, including atmospheric composition, global average temperatures, ocean conditions, among others. The report concluded the observed increase in tropical cyclone intensity is larger than climate models predict. In addition, the report considered that it is likely that storm intensity will continue to increase through the 21st century, and declared it more likely than not that there has been some human contribution to the increases in tropical cyclone intensity. However, there is no universal agreement about the magnitude of the effects anthropogenic global warming has on tropical cyclone formation, track, and intensity. For example, critics such as Chris Landsea assert that man-made effects would be "quite tiny compared to the observed large natural hurricane variability". A statement by the American Meteorological Society
    American Meteorological Society
    The American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, the American Meteorological Society has a membership...

     on 1 February 2007 stated that trends in tropical cyclone records offer "evidence both for and against the existence of a detectable anthropogenic signal" in tropical cyclogenesis
    Tropical cyclogenesis
    Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

    . Although many aspects of a link between tropical cyclones and global warming are still being "hotly debated", a point of agreement is that no individual tropical cyclone or season can be attributed to global warming. Research reported in the 3 September 2008 issue of Nature found that the strongest tropical cyclones are getting stronger, in particular over the North Atlantic and Indian oceans. Wind speeds for the strongest tropical storms increased from an average of 140 miles per hour (225.3 km/h) in 1981 to 156 miles per hour (251.1 km/h) in 2006, while the ocean temperature, averaged globally over the all regions where tropical cyclones form, increased from 28.2 °C (82.8 °F) to 28.5 °C (83.3 °F) during this period.

    Related cyclone types



    {{See also|Cyclone|Extratropical cyclone|Subtropical cyclone}}
    In addition to tropical cyclones, there are two other classes of cyclones within the spectrum of cyclone types. These kinds of cyclones, known as extratropical cyclone
    Extratropical cyclone
    Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

    s and subtropical cyclone
    Subtropical cyclone
    A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...

    s, can be stages a tropical cyclone passes through during its formation
    Tropical cyclogenesis
    Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

     or dissipation. An extratropical cyclone is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses; although not as frequently, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone. From space, extratropical storms have a characteristic "comma
    Comma (punctuation)
    The comma is a punctuation mark. It has the same shape as an apostrophe or single closing quotation mark in many typefaces, but it differs from them in being placed on the baseline of the text. Some typefaces render it as a small line, slightly curved or straight but inclined from the vertical, or...

    -shaped" cloud pattern. Extratropical cyclones can also be dangerous when their low-pressure centers cause powerful winds and high seas.

    A subtropical cyclone is a weather
    Weather
    Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...

     system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form in a wide band of latitude
    Latitude
    In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

    s, from the equator
    Equator
    An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

     to 50°. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm. From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.

    Tropical cyclones in popular culture


    {{Main|Tropical cyclones in popular culture}}
    In popular culture
    Popular culture
    Popular culture is the totality of ideas, perspectives, attitudes, memes, images and other phenomena that are deemed preferred per an informal consensus within the mainstream of a given culture, especially Western culture of the early to mid 20th century and the emerging global mainstream of the...

    , tropical cyclones have made appearances in different types of media, including films, books, television, music, and electronic game
    Electronic game
    An electronic game is a game that employs electronics to create an interactive system with which a player can play. The most common form of electronic game today is the video game, and for this reason the terms are often mistakenly used synonymously. Other common forms of electronic game include...

    s. The media can have tropical cyclones that are entirely fiction
    Fiction
    Fiction is the form of any narrative or informative work that deals, in part or in whole, with information or events that are not factual, but rather, imaginary—that is, invented by the author. Although fiction describes a major branch of literary work, it may also refer to theatrical,...

    al, or can be based on real events. For example, George Rippey Stewart's Storm
    Storm (novel)
    Storm is a novel written by George Rippey Stewart and published in 1941. The book became a best-seller and helped lead to the naming of tropical cyclones worldwide, even though the main character of the book was an extratropical cyclone.-Plot summary:...

    , a best-seller published in 1941, is thought to have influenced meteorologists into giving female names to Pacific tropical cyclones. Another example is the hurricane in The Perfect Storm
    The Perfect Storm (film)
    The Perfect Storm is a 2000 dramatic disaster film directed by Wolfgang Petersen. It is an adaptation of the 1997 non-fiction book of the same title by Sebastian Junger about the crew of the Andrea Gail that got caught in the Perfect Storm of 1991. The film stars George Clooney, Mark Wahlberg,...

    , which describes the sinking of the Andrea Gail
    Andrea Gail
    The F/V Andrea Gail was a commercial fishing vessel that was lost at sea with all hands during the "Perfect Storm" of 1991. The vessel and her six-man crew had been fishing the North Atlantic Ocean out of Gloucester, Massachusetts. Her last reported position was northeast of Sable Island on...

    by the 1991 Perfect Storm. Also, hypothetical hurricanes have been featured in parts of the plots of series such as The Simpsons
    Hurricane Neddy
    "Hurricane Neddy" is the eighth episode of The Simpsons eighth season which originally aired December 29, 1996. It was written by Steve Young, directed by Bob Anderson and features a cameo by Jon Lovitz as Jay Sherman from The Critic. In this episode, "Hurricane Barbara" viciously strikes...

    , Invasion
    Invasion (TV series)
    Invasion is an American science fiction television series that aired on ABC for only one season beginning in September 2005. Somewhat similar to Invasion of the Body Snatchers, the show told the story of the aftermath of a hurricane in which water-based creatures infiltrate a small Florida town and...

    , Family Guy, Seinfeld
    The Checks
    "The Checks" is the 141st episode of the sitcom Seinfeld. This was the 7th episode for the 8th season. It aired on NBC on November 7, 1996.-Plot:...

    , Dawson's Creek
    Dawson's Creek
    Dawson's Creek is an American teen drama television series which debuted on January 20, 1998, on The WB Television Network and was produced by Sony Pictures Television. The show is set in the fictional seaside town of Capeside, Massachusetts, and in Boston, Massachusetts, during the later seasons...

    , and CSI: Miami
    CSI: Miami (season 2)
    The second season of CSI: Miami premiered on CBS on September 22, 2003 and ended May 24, 2004.-Notable cast members:-Episodes:...

    . The 2004 film The Day After Tomorrow
    The Day After Tomorrow
    The Day After Tomorrow is a 2004 American science-fiction disaster film that depicts the catastrophic effects of global warming in a series of extreme weather events that usher in global cooling which leads to a new ice age. The film did well at the box office, grossing $542,771,772 internationally...

    includes several mentions of actual tropical cyclones as well as featuring fantastical "hurricane-like" non-tropical Arctic storms.

    See also


    {{Portal|Tropical cyclones}}
    {{multicol}}
    • Cyclone
      Cyclone
      In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...

    • Disaster preparedness
    • HURDAT
      HURDAT
      The North Atlantic hurricane database, or HURDAT, is the database for all tropical cyclones in the Atlantic Ocean, Gulf of Mexico and Caribbean Sea, since 1851.-History:...

       (online database)
    • Hurricane Alley
      Hurricane Alley
      Hurricane Alley is an area of warm water in the Atlantic Ocean stretching from the west coast of northern Africa to the east coast of central America and Gulf Coast of the southern United States. Many hurricanes form within this area...

    • Saffir–Simpson Hurricane Scale

    {{multicol-break}}
    • Hypercane
      Hypercane
      A hypercane is a hypothetical class of extreme hurricane that could form if ocean temperatures reached around , which is warmer than the warmest ocean temperature ever recorded. Such an increase could be caused by a large asteroid or comet impact, a large volcanic, supervolcanic eruption, or very...

    • List of wettest tropical cyclones by country
    • Secondary flow in tropical cyclones

    {{multicol-end}}

    {{Col-begin}}
    {{Col-2}}

    Annual seasons
    • List of Atlantic hurricane seasons (current)
    • List of North Indian Ocean cyclone seasons (current)
    • List of Pacific hurricane seasons (current)
    • List of Pacific typhoon seasons (current)
    • List of South-West Indian Ocean cyclone seasons ({{#time:Y}}-
      {{Redirect|Hurricane}}
      {{pp-move-indef}}
      A tropical cyclone is a storm system
      Storm
      A storm is any disturbed state of an astronomical body's atmosphere, especially affecting its surface, and strongly implying severe weather...

       characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclone
      Cyclone
      In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...

      s strengthen when water evaporated from the ocean is released as the saturated air rises, resulting in condensation
      Condensation
      Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

       of water vapor
      Water vapor
      Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

       contained in the moist air. They are fueled by a different heat mechanism than other cyclonic windstorms such as nor'easter
      Nor'easter
      A nor'easter is a type of macro-scale storm along the East Coast of the United States and Atlantic Canada, so named because the storm travels to the northeast from the south and the winds come from the northeast, especially in the coastal areas of the Northeastern United States and Atlantic Canada...

      s, European windstorm
      European windstorm
      A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

      s, and polar low
      Polar low
      A polar low is a small-scale, long-lived atmospheric low pressure system that is found over the ocean areas poleward of the main polar front in both the Northern and Southern Hemispheres. The systems usually have a horizontal length scale of less than and exist for no more than a couple of days. ...

      s. The characteristic that separates tropical cyclones from other cyclonic systems is that at any height in the atmosphere, the center of a tropical cyclone will be warmer than its surroundings; a phenomenon called "warm core" storm systems.

      The term "tropical" refers both to the geographical origin of these systems, which usually form in tropical
      Tropics
      The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately  N and the Tropic of Capricorn in the southern hemisphere at  S; these latitudes correspond to the axial tilt of the Earth...

       regions of the globe, and to their formation in maritime tropical air masses. The term "cyclone" refers to such storms' cyclonic nature, with counterclockwise wind flow in the Northern Hemisphere
      Northern Hemisphere
      The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

       and clockwise wind flow in the Southern Hemisphere
      Southern Hemisphere
      The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

      . The opposite direction of the wind flow is a result of the Coriolis force. Depending on its location and strength, a tropical cyclone is referred to by names such as hurricane (ˈhʌrɨkeɪn, ˈhʌrɨkən), typhoon, tropical storm, cyclonic storm, tropical depression, and simply cyclone.

      While tropical cyclones can produce extremely powerful winds and torrential rain
      Rain
      Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...

      , they are also able to produce high waves and damaging storm surge
      Storm surge
      A storm surge is an offshore rise of water associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea...

       as well as spawning tornadoes. They develop over large bodies of warm water, and lose their strength if they move over land due to increased surface friction and loss of the warm ocean as an energy source. This is why coastal regions can receive significant damage from a tropical cyclone, while inland regions are relatively safe from receiving strong winds. Heavy rains, however, can produce significant flooding inland, and storm surges can produce extensive coastal flood
      Flood
      A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

      ing up to 40 kilometres (24.9 mi) from the coastline. Although their effects on human populations can be devastating, tropical cyclones can relieve drought
      Drought
      A drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...

       conditions. They also carry heat energy away from the tropics and transport it toward temperate
      Temperate
      In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...

       latitudes, which makes them an important part of the global atmospheric circulation
      Atmospheric circulation
      Atmospheric circulation is the large-scale movement of air, and the means by which thermal energy is distributed on the surface of the Earth....

       mechanism. As a result, tropical cyclones help to maintain equilibrium in the Earth's troposphere
      Troposphere
      The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

      , and to maintain a relatively stable and warm temperature worldwide.

      Many tropical cyclones develop
      Tropical cyclogenesis
      Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

       when the atmospheric conditions around a weak disturbance in the atmosphere are favorable. The background environment is modulated by climatological cycles and patterns such as the Madden-Julian oscillation
      Madden-Julian oscillation
      The Madden–Julian oscillation ' is the largest element of the intraseasonal variability in the tropical atmosphere. It is a large-scale coupling between atmospheric circulation and tropical deep convection...

      , El Niño-Southern Oscillation
      El Niño-Southern Oscillation
      El Niño/La Niña-Southern Oscillation, or ENSO, is a quasiperiodic climate pattern that occurs across the tropical Pacific Ocean roughly every five years...

      , and the Atlantic multidecadal oscillation
      Atlantic Multidecadal Oscillation
      The Atlantic multidecadal oscillation is a mode of variability occurring in the North Atlantic Ocean and which has its principal expression in the sea surface temperature field...

      . Others form when other types of cyclones acquire tropical characteristics. Tropical systems are then moved by steering winds in the troposphere
      Troposphere
      The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

      ; if the conditions remain favorable, the tropical disturbance intensifies, and can even develop an eye
      Eye (cyclone)
      The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...

      . On the other end of the spectrum, if the conditions around the system deteriorate or the tropical cyclone makes landfall, the system weakens and eventually dissipates. It is not possible to artificially induce the dissipation of these systems with current technology.
      {{Tropicalcyclone}}

      Physical structure


      {{See also|Eye (cyclone)}}

      All tropical cyclones are areas of low
      Low pressure area
      A low-pressure area, or "low", is a region where the atmospheric pressure at sea level is below that of surrounding locations. Low-pressure systems form under areas of wind divergence which occur in upper levels of the troposphere. The formation process of a low-pressure area is known as...

       atmospheric pressure
      Atmospheric pressure
      Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

       in the Earth's atmosphere. The pressures recorded at the centers of tropical cyclones are among the lowest that occur on Earth's surface at sea level
      Sea level
      Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

      . Tropical cyclones are characterized and driven by the release of large amounts of latent heat of condensation, which occurs when moist air is carried upwards and its water vapor
      Water vapor
      Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...

       condenses. This heat is distributed vertically around the center of the storm. Thus, at any given altitude (except close to the surface, where water temperature dictates air temperature) the environment inside the cyclone is warmer than its outer surroundings.

      Eye and center


      A strong tropical cyclone will harbor an area of sinking air at the center of circulation. If this area is strong enough, it can develop into a large "eye". Weather in the eye is normally calm and free of clouds, although the sea may be extremely violent. The eye is normally circular in shape, and is typically 30–65 km (20–40 miles) in diameter
      Diameter
      In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints are on the circle. The diameters are the longest chords of the circle...

      , though eyes as small as 3 kilometres (1.9 mi) and as large as 370 kilometres (229.9 mi) have been observed. Intense, mature tropical cyclones can sometimes exhibit an outward curving of the eyewall's top, making it resemble an arena football stadium; this phenomenon is thus sometimes referred to as the stadium effect. It is usually coldest in the center.

      There are other features that either surround the eye, or cover it. The central dense overcast is the concentrated area of strong thunderstorm activity near the center of a tropical cyclone; in weaker tropical cyclones, the CDO may cover the center completely. The eyewall is a circle of strong thunderstorms that surrounds the eye; here is where the greatest wind speeds are found, where clouds reach the highest, and precipitation is the heaviest. The heaviest wind damage occurs where a tropical cyclone's eyewall passes over land. Eyewall replacement cycles occur naturally in intense tropical cyclones. When cyclones reach peak intensity they usually have an eyewall and radius of maximum wind
      Radius of maximum wind
      The radius of maximum wind is the distance between the center of a cyclone and its band of strongest winds. It is a parameter in atmospheric dynamics and tropical cyclone forecasting. The highest rainfall rates occur near the RMW of tropical cyclones. The extent of a cyclone's storm surge and...

      s that contract to a very small size, around 10 kilometres (6.2 mi) to 25 kilometres (15.5 mi). Outer rainbands can organize into an outer ring of thunderstorms that slowly moves inward and robs the inner eyewall of its needed moisture and angular momentum
      Angular momentum
      In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...

      . When the inner eyewall weakens, the tropical cyclone weakens (in other words, the maximum sustained winds weaken and the central pressure rises.) The outer eyewall replaces the inner one completely at the end of the cycle. The storm can be of the same intensity as it was previously or even stronger after the eyewall replacement cycle finishes. The storm may strengthen again as it builds a new outer ring for the next eyewall replacement.
      Size descriptions of tropical cyclones
      ROCI Type
      Less than 2 degrees latitude Very small/midget
      2 to 3 degrees of latitude Small
      3 to 6 degrees of latitude Medium/Average
      6 to 8 degrees of latitude Large
      Over 8 degrees of latitude Very large

      Size


      One measure of the size of a tropical cyclone is determined by measuring the distance from its center of circulation to its outermost closed isobar, also known as its ROCI
      Radius of outermost closed isobar
      style="float: right; clear: right; background-color: transparent; margin-left: 0em"|The radius of outermost closed isobar is one of the quantities used to determine the size of a tropical cyclone. It is determined by measuring the radii from the center of the storm to its outermost closed isobar...

      . If the radius is less than two degrees of latitude
      Latitude
      In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

       or 222 kilometres (137.9 mi), then the cyclone is "very small" or a "midget". A radius between 3 and 6 latitude degrees or 333 kilometres (206.9 mi) to 670 kilometres (416.3 mi) are considered "average-sized". "Very large" tropical cyclones have a radius of greater than 8 degrees or 888 kilometres (551.8 mi). Use of this measure has objectively determined that tropical cyclones in the northwest Pacific Ocean are the largest on earth on average, with Atlantic tropical cyclones roughly half their size. Other methods of determining a tropical cyclone's size include measuring the radius of gale force winds and measuring the radius at which its relative vorticity field decreases to 1×10−5 s−1 from its center.

      Mechanics


      A tropical cyclone's primary energy source is the release of the heat of condensation from water vapor condensing
      Condensation
      Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....

      , with solar heating being the initial source for evaporation. Therefore, a tropical cyclone can be visualized as a giant vertical heat engine
      Heat engine
      In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...

       supported by mechanics driven by physical forces such as the rotation
      Rotation
      A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...

       and gravity of the Earth. In another way, tropical cyclones could be viewed as a special type of mesoscale convective complex
      Mesoscale Convective Complex
      A mesoscale convective complex is a unique kind of mesoscale convective system which is defined by characteristics observed in infrared satellite imagery. They are long-lived, nocturnal in formation and commonly contain heavy rainfall, wind, hail, lightning and possibly tornadoes.-Size:A...

      , which continues to develop over a vast source of relative warmth and moisture. While an initial warm core system, such as an organized thunderstorm complex, is necessary for the formation of a tropical cyclone, a large flux of energy is needed to lower atmospheric pressure
      Atmospheric pressure
      Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

       more than a few millibars (0.10 inch of mercury
      Mercury (element)
      Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

      ). The inflow
      Inflow (meteorology)
      Inflow is the flow of a fluid into a large collection of that fluid. Within meteorology, inflow normally refers to the influx of warmth and moisture from air within the Earth's atmosphere into storm systems. Extratropical cyclones are fed by inflow focused along their cold front and warm fronts...

       of warmth and moisture from the underlying ocean surface is critical for tropical cyclone strengthening. A significant amount of the inflow in the cyclone is in the lowest 1 kilometres (3,280.8 ft) of the atmosphere.

      Condensation leads to higher wind speeds, as a tiny fraction of the released energy is converted into mechanical energy; the faster winds and lower pressure associated with them in turn cause increased surface evaporation and thus even more condensation. Much of the released energy drives updrafts
      Vertical draft
      An updraft or downdraft is the vertical movement of air as a weather related phenomenon. One of two forces causes the air to move. Localized regions of warm or cool air will exhibit vertical movement. A mass of warm air will typically be less dense than the surrounding region, and so will rise...

       that increase the height of the storm clouds, speeding up condensation. This positive feedback loop, called the Wind-induced surface heat exchange
      Wind-induced surface heat exchange
      The wind-induced surface heat exchange is a positive feedback mechanism between the ocean and atmosphere in which a stronger ocean-to-atmosphere heat flux results in a stronger atmospheric circulation, which results in a strong heat flux. It has been hypothesized that this is the mechanism that...

      , continues for as long as conditions are favorable for tropical cyclone development
      Tropical cyclogenesis
      Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

      . Factors such as a continued lack of equilibrium in air mass distribution would also give supporting energy to the cyclone. The rotation of the Earth causes the system to spin, an effect known as the Coriolis effect
      Coriolis effect
      In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

      , giving it a cyclonic characteristic and affecting the trajectory of the storm. In the Northern Hemisphere
      Northern Hemisphere
      The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

      , where the cyclone's wind flow is counterclockwise, the fastest winds relative to the surface of the Earth occur on the eastern side of a northward-moving storm and on the northern side of a westward-moving one; the opposite occurs in the Southern Hemisphere
      Southern Hemisphere
      The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

      , where the wind flow is clockwise
      Clockwise
      Circular motion can occur in two possible directions. A clockwise motion is one that proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back to the top...

      .

      What primarily distinguishes tropical cyclones from other meteorological phenomena is deep convection
      Deep convection
      Deep convection is a convective process in a medium, usually in an atmosphere or ocean, that in some sense spans the vertical.Within the atmosphere, this means from the surface to above the 500 hPa level, generally stopping at or defining the tropopause at around 200 hPa...

       as a driving force. Because convection is strongest in a tropical climate
      Tropical climate
      A tropical climate is a climate of the tropics. In the Köppen climate classification it is a non-arid climate in which all twelve months have mean temperatures above...

      , it defines the initial domain of the tropical cyclone. By contrast, mid-latitude cyclone
      Mid-latitude cyclone
      Cyclogenesis is the development or strengthening of cyclonic circulation in the atmosphere . Cyclogenesis is an umbrella term for several different processes, all of which result in the development of some sort of cyclone. It can occur at various scales, from the microscale to the synoptic scale...

      s draw their energy mostly from pre-existing horizontal temperature gradient
      Gradient
      In vector calculus, the gradient of a scalar field is a vector field that points in the direction of the greatest rate of increase of the scalar field, and whose magnitude is the greatest rate of change....

      s in the atmosphere. To continue to drive its heat engine, a tropical cyclone must remain over warm water, which provides the needed atmospheric moisture to keep the positive feedback loop running. When a tropical cyclone passes over land, it is cut off from its heat source and its strength diminishes rapidly.


      The passage of a tropical cyclone over the ocean causes the upper layers of the ocean to cool substantially, which can influence subsequent cyclone development. This cooling is primarily caused by wind-driven mixing of cold water from deeper in the ocean and the warm surface waters. This effect results in a negative feedback process that can inhibit further development or lead to weakening. Additional cooling may come in the form of cold water from falling raindrops (this is because the atmosphere is cooler at higher altitudes). Cloud cover may also play a role in cooling the ocean, by shielding the ocean surface from direct sunlight before and slightly after the storm passage. All these effects can combine to produce a dramatic drop in sea surface temperature over a large area in just a few days.

      Scientists estimate that a tropical cyclone releases heat energy at the rate of 50 to 200 exajoules (1018 J) per day, equivalent to about 1 PW (1015 watt). This rate of energy release is equivalent to 70 times the world energy consumption
      World energy resources and consumption
      ]World energy consumption in 2010: over 5% growthEnergy markets have combined crisis recovery and strong industry dynamism. Energy consumption in the G20 soared by more than 5% in 2010, after the slight decrease of 2009. This strong increase is the result of two converging trends...

       of humans and 200 times the worldwide electrical generating capacity, or to exploding a 10-megaton
      TNT equivalent
      TNT equivalent is a method of quantifying the energy released in explosions. The ton of TNT is a unit of energy equal to 4.184 gigajoules, which is approximately the amount of energy released in the detonation of one ton of TNT...

       nuclear bomb every 20 minutes.

      In the lower troposphere, the most obvious motion of clouds is toward the center. However tropical cyclones also develop an upper-level (high-altitude) outward flow of clouds. These originate from air that has released its moisture and is expelled at high altitude through the "chimney" of the storm engine. This outflow produces high, cirrus cloud
      Cirrus cloud
      Cirrus clouds are atmospheric clouds generally characterized by thin, wispy strands, giving them their name from the Latin word cirrus meaning a ringlet or curling lock of hair...

      s that spiral away from the center. The clouds thin as they move outwards from the center of the system and are evaporated. They may be thin enough for the sun to be visible through them. These high cirrus clouds may be the first signs of an approaching tropical cyclone. As air parcels are lifted within the eye of the storm the vorticity is reduced, causing the outflow from a tropical cyclone to have anti-cyclonic motion.

      Major basins and related warning centers


      {{Main|Tropical cyclone basins|Regional Specialized Meteorological Center}}
      Basins and WMO
      World Meteorological Organization
      The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

       Monitoring Institutions
      Basin Responsible RSMCs and TCWCs
      North Atlantic National Hurricane Center
      National Hurricane Center
      The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...

       (United States)
      North-East Pacific National Hurricane Center
      National Hurricane Center
      The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...

       (United States)
      North-Central Pacific Central Pacific Hurricane Center
      Central Pacific Hurricane Center
      The Central Pacific Hurricane Center of the United States National Weather Service is the official body responsible for tracking and issuing tropical cyclone warnings, watches, advisories, discussions, and statements for the Central North Pacific Basin...

       (United States)
      North-West Pacific Japan Meteorological Agency
      Japan Meteorological Agency
      The or JMA, is the Japanese government's weather service. Charged with gathering and reporting weather data and forecasts in Japan, it is a semi-autonomous part of the Ministry of Land, Infrastructure and Transport...

      North Indian Ocean India Meteorological Department
      India Meteorological Department
      The India Meteorological Department , also referred to as the Met Office, is an agency of the Ministry of Earth Sciences of the Government of India. It is the principal agency responsible for meteorological observations, weather forecasting and seismology...

      South-West Indian Ocean Météo-France
      Météo-France
      Météo-France is the French national meteorological service.The organisation was established by decree in June 1993 and is a department of the Ministry of Transportation. It is headquartered in Paris but many domestic operations have been decentralised to Toulouse...

      Australian region Bureau of Meteorology
      Bureau of Meteorology
      The Bureau of Meteorology is an Executive Agency of the Australian Government responsible for providing weather services to Australia and surrounding areas. It was established in 1906 under the Meteorology Act, and brought together the state meteorological services that existed before then...

      (Australia)
      Meteorological and Geophysical Agency (Indonesia)
      Papua New Guinea National Weather Service
      Southern Pacific Fiji Meteorological Service
      Fiji Meteorological Service
      The Fiji Meteorological Service is a Department of the government of Fiji responsible for providing weather forecasts and is based in Nadi. Since 1995, FMS has been responsible for naming and tracking tropical cyclones in the Southwest Pacific region...


      Meteorological Service of New Zealand
      : Indicates a Tropical Cyclone Warning Center


      There are six Regional Specialized Meteorological Center
      Regional Specialized Meteorological Center
      A Regional Specialized Meteorological Centre is responsible for the distribution of information, advisories, and warnings regarding the specific program they have a part of, agreed by consensus at the World Meteorological Organization as part of the World Weather Watch.-Tropical...

      s (RSMCs) worldwide. These organizations are designated by the World Meteorological Organization
      World Meteorological Organization
      The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

       and are responsible for tracking and issuing bulletins, warnings, and advisories about tropical cyclones in their designated areas of responsibility. In addition, there are six Tropical Cyclone Warning Centers (TCWCs) that provide information to smaller regions. The RSMCs and TCWCs are not the only organizations that provide information about tropical cyclones to the public. The Joint Typhoon Warning Center
      Joint Typhoon Warning Center
      The Joint Typhoon Warning Center is a joint United States Navy – United States Air Force task force located at the Naval Maritime Forecast Center in Pearl Harbor, Hawaii...

       (JTWC) issues advisories in all basins except the Northern Atlantic for the purposes of the United States Government. The Philippine Atmospheric, Geophysical and Astronomical Services Administration
      Philippine Atmospheric, Geophysical and Astronomical Services Administration
      The Philippine Atmospheric, Geophysical and Astronomical Services Administration is a Philippine national institution dedicated to provide flood and typhoon warnings, public weather forecasts and advisories, meteorological, astronomical, climatological, and other specialized information and...

       (PAGASA) issues advisories and names for tropical cyclones that approach the Philippines
      Philippines
      The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

       in the Northwestern Pacific to protect the life and property of its citizens. The Canadian Hurricane Center (CHC) issues advisories on hurricanes and their remnants for Canadian citizens when they affect Canada.

      On 26 March 2004, Cyclone Catarina
      Cyclone Catarina
      Cyclone Catarina is one of several informal names for a South Atlantic tropical cyclone that hit southeastern Brazil in late March 2004. The storm developed out of a stationary cold-core upper-level trough on March 12...

       became the first recorded South Atlantic cyclone
      South Atlantic tropical cyclone
      South Atlantic tropical cyclones are unusual weather events that occur in the southern hemisphere. Strong wind shear and a lack of weather disturbances favorable for tropical cyclone development make any hurricane-strength cyclones extremely rare...

       and subsequently struck southern Brazil
      Brazil
      Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

       with winds equivalent to Category 2 on the Saffir-Simpson Hurricane Scale
      Saffir-Simpson Hurricane Scale
      The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...

      . As the cyclone formed outside the authority of another warning center, Brazilian meteorologists initially treated the system as an extratropical cyclone
      Extratropical cyclone
      Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

      , although subsequently classified it as tropical.

      Formation


      {{Main|Tropical cyclogenesis}}


      Worldwide, tropical cyclone activity peaks in late summer, when the difference between temperatures aloft and sea surface temperatures is the greatest. However, each particular basin has its own seasonal patterns. On a worldwide scale, May is the least active month, while September is the most active while November is the only month with all the tropical cyclone basins active.

      Times


      In the Northern Atlantic Ocean
      Atlantic Ocean
      The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

      , a distinct cyclone season
      Atlantic hurricane season
      The Atlantic hurricane season is the period in a year when hurricanes usually form in the Atlantic Ocean. Tropical cyclones in the North Atlantic are called hurricanes, tropical storms, or tropical depressions. In addition, there have been several storms over the years that have not been fully...

       occurs from June 1 to November 30, sharply peaking from late August through September. The statistical peak of the Atlantic hurricane season is 10 September. The Northeast Pacific Ocean
      Pacific Ocean
      The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

       has a broader period of activity, but in a similar time frame to the Atlantic. The Northwest Pacific sees tropical cyclones year-round, with a minimum in February and March and a peak in early September. In the North Indian basin, storms are most common from April to December, with peaks in May and November. In the Southern Hemisphere
      Southern Hemisphere
      The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

      , the tropical cyclone year begins on July 1 and runs all year-round and encompasses the tropical cyclone seasons, which run from November 1 until the end of April, with peaks in mid-February to early March.

      Season lengths and seasonal averages
      Basin Season start Season end Tropical Storms
      (>34 knots)
      Tropical Cyclones
      (>63 knots)
      Category 3+ TCs
      (>95 knots)
      Northwest Pacific April January 26.7 16.9 8.5
      South Indian November April 20.6 10.3 4.3
      Northeast Pacific May November 16.3 9.0 4.1
      North Atlantic June November 10.6 5.9 2.0
      Australia Southwest Pacific November April 9 4.8 1.9
      North Indian April December 5.4 2.2 0.4


      Factors


      The formation of tropical cyclones is the topic of extensive ongoing research and is still not fully understood. While six factors appear to be generally necessary, tropical cyclones may occasionally form without meeting all of the following conditions. In most situations, water temperatures
      Sea surface temperature
      Sea surface temperature is the water temperature close to the oceans surface. The exact meaning of surface varies according to the measurement method used, but it is between and below the sea surface. Air masses in the Earth's atmosphere are highly modified by sea surface temperatures within a...

       of at least 26.5 °C (79.7 °F) are needed down to a depth of at least 50 m (164 ft); waters of this temperature cause the overlying atmosphere to be unstable enough to sustain convection and thunderstorms. Another factor is rapid cooling with height, which allows the release of the heat of condensation that powers a tropical cyclone. High humidity is needed, especially in the lower-to-mid troposphere
      Troposphere
      The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

      ; when there is a great deal of moisture in the atmosphere, conditions are more favorable for disturbances to develop. Low amounts of wind shear
      Wind shear
      Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...

       are needed, as high shear is disruptive to the storm's circulation. Tropical cyclones generally need to form more than 555 km (344.9 mi) or 5 degrees of latitude
      Latitude
      In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

       away from the equator
      Equator
      An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

      , allowing the Coriolis effect
      Coriolis effect
      In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

       to deflect winds blowing towards the low pressure center and creating a circulation. Lastly, a formative tropical cyclone needs a pre-existing system of disturbed weather, although without a circulation no cyclonic development will take place. Low-latitude and low-level westerly wind bursts associated with the Madden-Julian oscillation
      Madden-Julian oscillation
      The Madden–Julian oscillation ' is the largest element of the intraseasonal variability in the tropical atmosphere. It is a large-scale coupling between atmospheric circulation and tropical deep convection...

       can create favorable conditions for tropical cyclogenesis by initiating tropical disturbances.

      Locations


      Most tropical cyclones form in a worldwide band of thunderstorm activity called by several names: the Intertropical Front (ITF), the Intertropical Convergence Zone
      Intertropical Convergence Zone
      The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....

       (ITCZ), or the monsoon trough
      Monsoon trough
      The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...

      . Another important source of atmospheric instability is found in tropical wave
      Tropical wave
      Tropical waves, easterly waves, or tropical easterly waves, also known as African easterly waves in the Atlantic region, are a type of atmospheric trough, an elongated area of relatively low air pressure, oriented north to south, which move from east to west across the tropics causing areas of...

      s, which cause about 85% of intense tropical cyclones in the Atlantic ocean, and become most of the tropical cyclones in the Eastern Pacific basin.

      Tropical cyclones move westward when equatorward of the subtropical ridge
      Subtropical ridge
      The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

      , intensifying as they move. Most of these systems form between 10 and 30 degrees away of the equator
      Equator
      An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

      , and 87% form no farther away than 20 degrees of latitude, north or south. Because the Coriolis effect
      Coriolis effect
      In physics, the Coriolis effect is a deflection of moving objects when they are viewed in a rotating reference frame. In a reference frame with clockwise rotation, the deflection is to the left of the motion of the object; in one with counter-clockwise rotation, the deflection is to the right...

       initiates and maintains tropical cyclone rotation, tropical cyclones rarely form or move within about 5 degrees of the equator, where the Coriolis effect is weakest. However, it is possible for tropical cyclones to form within this boundary as Tropical Storm Vamei
      Tropical Storm Vamei
      Tropical Storm Vamei was a Pacific tropical cyclone that formed closer to the equator than any other tropical cyclone worldwide...

       did in 2001 and Cyclone Agni
      Cyclone Agni
      Severe Cyclonic Storm Agni was a tropical cyclone of the 2004 North Indian Ocean cyclone season notable for its record proximity to the equator. It was the second North Indian Ocean cyclone to receive a name, after Onil earlier in the year...

       in 2004.

      Steering winds


      {{See also|Prevailing winds}}
      Although tropical cyclones are large systems generating enormous energy, their movements over the Earth's surface are controlled by large-scale winds—the streams in the Earth's atmosphere. The path of motion is referred to as a tropical cyclone's track and has been compared by Dr. Neil Frank, former director of the National Hurricane Center
      National Hurricane Center
      The National Hurricane Center , located at Florida International University in Miami, Florida, is the division of the National Weather Service responsible for tracking and predicting weather systems within the tropics between the Prime Meridian and the 140th meridian west poleward to the 30th...

      , to "leaves carried along by a stream".

      Tropical systems, while generally located equator
      Equator
      An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

      ward of the 20th parallel, are steered primarily westward by the east-to-west winds on the equatorward side of the subtropical ridge
      Subtropical ridge
      The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

      —a persistent high-pressure area over the world's oceans. In the tropical North Atlantic and Northeast Pacific oceans, trade winds—another name for the westward-moving wind currents—steer tropical waves westward from the African coast and towards the Caribbean Sea, North America, and ultimately into the central Pacific ocean before the waves dampen out. These waves are the precursors to many tropical cyclones within this region. In the Indian Ocean
      Indian Ocean
      The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...

       and Western Pacific (both north and south of the equator), tropical cyclogenesis is strongly influenced by the seasonal movement of the Intertropical Convergence Zone
      Intertropical Convergence Zone
      The Intertropical Convergence Zone , known by sailors as The Doldrums, is the area encircling the earth near the equator where winds originating in the northern and southern hemispheres come together....

       and the monsoon trough
      Monsoon trough
      The monsoon trough is that portion of the Intertropical Convergence Zone which extends into or through a monsoon circulation, as depicted by a line on a weather map showing the locations of minimum sea level pressure, and as such, is a convergence zone between the wind patterns of the southern and...

      , rather than by easterly waves. Tropical cyclones can also be steered by other systems, such as other low pressure systems, high pressure systems, warm front
      Warm front
      A warm front is a density discontinuity located at the leading edge of a homogeneous warm air mass, and is typically located on the equator-facing edge of an isotherm gradient...

      s, and cold front
      Cold front
      A cold front is defined as the leading edge of a cooler mass of air, replacing a warmer mass of air.-Development of cold front:The cooler and denser air wedges under the less-dense warmer air, lifting it...

      s.

      Coriolis effect



      The Earth's rotation imparts an acceleration known as the Coriolis effect, Coriolis acceleration, or colloquially, Coriolis force. This acceleration causes cyclonic systems to turn towards the poles in the absence of strong steering currents. The poleward portion of a tropical cyclone contains easterly winds, and the Coriolis effect pulls them slightly more poleward. The westerly winds on the equatorward portion of the cyclone pull slightly towards the equator, but, because the Coriolis effect weakens toward the equator, the net drag on the cyclone is poleward. Thus, tropical cyclones in the Northern Hemisphere usually turn north (before being blown east), and tropical cyclones in the Southern Hemisphere usually turn south (before being blown east) when no other effects counteract the Coriolis effect.

      The Coriolis effect also initiates cyclonic rotation, but it is not the driving force that brings this rotation to high speeds – that force is the heat of condensation.

      Interaction with the mid-latitude westerlies


      {{See also|Westerlies}}

      When a tropical cyclone crosses the subtropical ridge
      Subtropical ridge
      The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

       axis, its general track around the high-pressure area is deflected significantly by winds moving towards the general low-pressure area to its north. When the cyclone track becomes strongly poleward with an easterly component, the cyclone has begun recurvature. A typhoon moving through the Pacific Ocean towards Asia, for example, will recurve offshore of Japan to the north, and then to the northeast, if the typhoon encounters southwesterly winds (blowing northeastward) around a low-pressure system passing over China or Siberia
      Siberia
      Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...

      . Many tropical cyclones are eventually forced toward the northeast by extratropical cyclone
      Extratropical cyclone
      Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

      s in this manner, which move from west to east to the north of the subtropical ridge. An example of a tropical cyclone in recurvature was Typhoon Ioke
      Hurricane Ioke
      Hurricane Ioke was the strongest hurricane ever recorded in the Central Pacific...

       in 2006, which took a similar trajectory.

      Landfall


      {{See also|List of notable tropical cyclones|Tropical cyclogenesis#Unusual areas of formation|l2=Unusual areas of tropical cyclone formation}}
      Officially, landfall
      Landfall (meteorology)
      Landfall is the event of a tropical cyclone or a waterspout coming onto land after being over water. When a waterspout makes landfall it is reclassified as a tornado, which can then cause damage inland...

      is when a storm's center (the center of its circulation, not its edge) crosses the coastline. Storm conditions may be experienced on the coast and inland hours before landfall; in fact, a tropical cyclone can launch its strongest winds over land, yet not make landfall; if this occurs, then it is said that the storm made a direct hit on the coast. As a result of the narrowness of this definition, the landfall area experiences half of a land-bound storm by the time the actual landfall occurs. For emergency preparedness, actions should be timed from when a certain wind speed or intensity of rainfall will reach land, not from when landfall will occur.

      Multiple storm interaction


      {{Main|Fujiwhara effect}}
      When two cyclones approach one another, their centers will begin orbiting cyclonically about a point between the two systems. The two vortices will be attracted to each other, and eventually spiral into the center point and merge. When the two vortices are of unequal size, the larger vortex will tend to dominate the interaction, and the smaller vortex will orbit around it. This phenomenon is called the Fujiwhara effect, after Sakuhei Fujiwhara
      Sakuhei Fujiwhara
      was a Japanese meteorologist who became the namesake for the Fujiwhara effect. Novelist Jirō Nitta is his nephew and mathematician Masahiko Fujiwara is his grandnephew.-Early life:...

      .

      Factors



      A tropical cyclone can cease to have tropical characteristics in several different ways. One such way is if it moves over land, thus depriving it of the warm water it needs to power itself, quickly losing strength. Most strong storms lose their strength very rapidly after landfall and become disorganized areas of low pressure within a day or two, or evolve into extratropical cyclone
      Extratropical cyclone
      Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

      s. There is a chance a tropical cyclone could regenerate if it managed to get back over open warm water, such as with Hurricane Ivan
      Hurricane Ivan
      Hurricane Ivan was a large, long-lived, Cape Verde-type hurricane that caused widespread damage in the Caribbean and United States. The cyclone was the ninth named storm, the sixth hurricane and the fourth major hurricane of the active 2004 Atlantic hurricane season...

      . If it remains over mountains for even a short time, weakening will accelerate. Many storm fatalities occur in mountainous terrain, as the dying storm unleashes torrential rainfall, leading to deadly flood
      Flood
      A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...

      s and mudslides, similar to those that happened with Hurricane Mitch
      Hurricane Mitch
      Hurricane Mitch was the most powerful hurricane and the most destructive of the 1998 Atlantic hurricane season, with maximum sustained winds of 180 mph . The storm was the thirteenth tropical storm, ninth hurricane, and third major hurricane of the season. Along with Hurricane Georges, Mitch...

       in 1998. In addition, dissipation can occur if a storm remains in the same area of ocean for too long, mixing the upper 60 metres (196.9 ft) of water, dropping sea surface temperatures more than 5 °C (9 °F). Without warm surface water, the storm cannot survive.

      A tropical cyclone can dissipate when it moves over waters significantly below 26.5 °C (79.7 °F). This will cause the storm to lose its tropical characteristics (i.e. thunderstorms near the center and warm core) and become a remnant low pressure area, which can persist for several days. This is the main dissipation mechanism in the Northeast Pacific ocean. Weakening or dissipation can occur if it experiences vertical wind shear
      Wind shear
      Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...

      , causing the convection and heat engine to move away from the center; this normally ceases development of a tropical cyclone. In addition, its interaction with the main belt of the Westerlies, by means of merging with a nearby frontal zone, can cause tropical cyclones to evolve into extratropical cyclones. This transition can take 1–3 days. Even after a tropical cyclone is said to be extratropical or dissipated, it can still have tropical storm force (or occasionally hurricane/typhoon force) winds and drop several inches of rainfall. In the Pacific ocean
      Pacific Ocean
      The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

       and Atlantic ocean
      Atlantic Ocean
      The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

      , such tropical-derived cyclones of higher latitudes can be violent and may occasionally remain at hurricane or typhoon-force wind speeds when they reach the west coast of North America. These phenomena can also affect Europe, where they are known as European windstorm
      European windstorm
      A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

      s
      ; Hurricane Iris's
      Hurricane Iris (1995)
      Hurricane Iris was the ninth named tropical cyclone and fifth hurricane of an active 1995 Atlantic hurricane season. Iris was one of four storms to form nearly simultaneously in the Atlantic during the 1995 season. Forming on August 22, Iris slowly drifted across the Leeward Islands as a tropical...

       extratropical remnants are an example of such a windstorm from 1995. In addition, a cyclone can merge with another area of low pressure, becoming a larger area of low pressure. This can strengthen the resultant system, although it may no longer be a tropical cyclone. Studies in the 2000s have given rise to the hypothesis that large amounts of dust reduce the strength of tropical cyclones.

      Artificial dissipation


      In the 1960s and 1970s, the United States government attempted to weaken hurricanes through Project Stormfury
      Project Stormfury
      Project Stormfury was an attempt to weaken tropical cyclones by flying aircraft into them and seeding with silver iodide. The project was run by the United States Government from 1962 to 1983....

       by seeding
      Cloud seeding
      Cloud seeding, a form of intentional weather modification, is the attempt to change the amount or type of precipitation that falls from clouds, by dispersing substances into the air that serve as cloud condensation or ice nuclei, which alter the microphysical processes within the cloud...

       selected storms with silver iodide
      Silver iodide
      Silver iodide is a yellow, inorganic, photosensitive iodide of silver used in photography, in medicine as an antiseptic, and in rainmaking for cloud seeding.-Crystal structure:...

      . It was thought that the seeding would cause supercooled water in the outer rainbands to freeze, causing the inner eyewall to collapse and thus reducing the winds. The winds of Hurricane Debbie
      Hurricane Debbie (1969)
      Hurricane Debbie was an intense and long-lived hurricane that formed during August 1969. The fifth tropical cyclone, fourth named storm, third hurricane and second major hurricane of the 1969 Atlantic hurricane season, Debbie formed on August 14 in the southern Atlantic Ocean and took a general...

      —a hurricane seeded in Project Stormfury—dropped as much as 31%, but Debbie regained its strength after each of two seeding forays. In an earlier episode in 1947, disaster struck when a hurricane east of Jacksonville, Florida
      Jacksonville, Florida
      Jacksonville is the largest city in the U.S. state of Florida in terms of both population and land area, and the largest city by area in the contiguous United States. It is the county seat of Duval County, with which the city government consolidated in 1968...

       promptly changed its course after being seeded, and smashed into Savannah, Georgia
      Savannah, Georgia
      Savannah is the largest city and the county seat of Chatham County, in the U.S. state of Georgia. Established in 1733, the city of Savannah was the colonial capital of the Province of Georgia and later the first state capital of Georgia. Today Savannah is an industrial center and an important...

      . Because there was so much uncertainty about the behavior of these storms, the federal government would not approve seeding operations unless the hurricane had a less than 10% chance of making landfall within 48 hours, greatly reducing the number of possible test storms. The project was dropped after it was discovered that eyewall replacement cycles occur naturally in strong hurricanes, casting doubt on the result of the earlier attempts. Today, it is known that silver iodide seeding is not likely to have an effect because the amount of supercooled water in the rainbands of a tropical cyclone is too low.

      Other approaches have been suggested over time, including cooling the water under a tropical cyclone by towing iceberg
      Iceberg
      An iceberg is a large piece of ice from freshwater that has broken off from a snow-formed glacier or ice shelf and is floating in open water. It may subsequently become frozen into pack ice...

      s into the tropical oceans. Other ideas range from covering the ocean in a substance that inhibits evaporation, dropping large quantities of ice into the eye at very early stages of development (so that the latent heat is absorbed by the ice, instead of being converted to kinetic energy that would feed the positive feedback loop), or blasting the cyclone apart with nuclear weapons. Project Cirrus even involved throwing dry ice on a cyclone. These approaches all suffer from one flaw above many others: tropical cyclones are simply too large and short-lived for any of the weakening techniques to be practical.

      Effects



      {{Main|Effects of tropical cyclones}}
      Tropical cyclones out at sea cause large waves, heavy rain, and high winds, disrupting international shipping and, at times, causing shipwrecks. Tropical cyclones stir up water, leaving a cool wake behind them, which causes the region to be less favorable for subsequent tropical cyclones. On land, strong wind
      Wind
      Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...

      s can damage or destroy vehicles, buildings, bridges, and other outside objects, turning loose debris into deadly flying projectiles. The storm surge
      Storm surge
      A storm surge is an offshore rise of water associated with a low pressure weather system, typically tropical cyclones and strong extratropical cyclones. Storm surges are caused primarily by high winds pushing on the ocean's surface. The wind causes the water to pile up higher than the ordinary sea...

      , or the increase in sea level due to the cyclone, is typically the worst effect from landfalling tropical cyclones, historically resulting in 90% of tropical cyclone deaths.
      The broad rotation of a landfalling tropical cyclone, and vertical wind shear at its periphery, spawns tornadoes
      History of tropical cyclone-spawned tornadoes
      Intense tropical cyclones usually produce tornadoes, the majority of them weak, especially upon landfall.- List of Atlantic tropical cyclones which spawned tornadoes :These are the Atlantic tropical cyclones that are known to have spawned tornadoes in the U.S....

      . Tornadoes can also be spawned as a result of eyewall mesovortices, which persist until landfall.

      Over the past two centuries, tropical cyclones have been responsible for the deaths of about 1.9 million people worldwide. Large areas of standing water caused by flooding lead to infection, as well as contributing to mosquito-borne illnesses. Crowded evacuees in shelters
      Emergency shelter
      Emergency shelters are places for people to live temporarily when they can't live in their previous residence, similar to homeless shelters. The main difference is that an emergency shelter typically specializes in people fleeing a specific type of situation, such as natural or man-made disasters,...

       increase the risk of disease propagation. Tropical cyclones significantly interrupt infrastructure, leading to power outages, bridge destruction, and the hampering of reconstruction efforts.

      Although cyclones take an enormous toll in lives and personal property, they may be important factors in the precipitation
      Precipitation (meteorology)
      In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...

       regimes of places they impact, as they may bring much-needed precipitation to otherwise dry regions. Tropical cyclones also help maintain the global heat balance by moving warm, moist tropical air to the middle latitudes
      Middle latitudes
      The middle latitudes are between 23°26'22" North and 66°33'39" North, and between 23°26'22" South and 66°33'39" South latitude, or, the Earth's temperate zones between the tropics and the Arctic and Antarctic. The prevailing winds in the middle latitudes are often very strong...

       and polar regions, and by regulating the thermohaline circulation
      Thermohaline circulation
      The term thermohaline circulation refers to a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes....

       through upwelling
      Upwelling
      Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water. The increased availability in upwelling regions results in high levels of primary...

      . The storm surge and winds of hurricanes may be destructive to human-made structures, but they also stir up the waters of coastal estuaries
      Estuary
      An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

      , which are typically important fish breeding locales. Tropical cyclone destruction spurs redevelopment, greatly increasing local property values.

      Observation


      {{Main|Tropical cyclone observation}}

      Intense tropical cyclones pose a particular observation challenge, as they are a dangerous oceanic phenomenon, and weather station
      Weather station
      A weather station is a facility, either on land or sea, with instruments and equipment for observing atmospheric conditions to provide information for weather forecasts and to study the weather and climate. The measurements taken include temperature, barometric pressure, humidity, wind speed, wind...

      s, being relatively sparse, are rarely available on the site of the storm itself. In general, surface observations are available only if the storm is passing over an island or a coastal area, or if there is a nearby ship. Real-time measurements are usually taken in the periphery of the cyclone, where conditions are less catastrophic and its true strength cannot be evaluated. For this reason, there are teams of meteorologists that move into the path of tropical cyclones to help evaluate their strength at the point of landfall.

      Tropical cyclones far from land are tracked by weather satellite
      Weather satellite
      The weather satellite is a type of satellite that is primarily used to monitor the weather and climate of the Earth. Satellites can be either polar orbiting, seeing the same swath of the Earth every 12 hours, or geostationary, hovering over the same spot on Earth by orbiting over the equator while...

      s capturing visible and infrared
      Infrared
      Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...

       images from space, usually at half-hour to quarter-hour intervals. As a storm approaches land, it can be observed by land-based Doppler
      Pulse-doppler radar
      Pulse-Doppler is a 4D radar system capable of detecting both target 3D location as well as measuring radial velocity . It uses the Doppler effect to avoid overloading computers and operators as well as to reduce power consumption...

       radar
      Weather radar
      Weather radar, also called weather surveillance radar and Doppler weather radar, is a type of radar used to locate precipitation, calculate its motion, estimate its type . Modern weather radars are mostly pulse-Doppler radars, capable of detecting the motion of rain droplets in addition to the...

      . Radar plays a crucial role around landfall by showing a storm's location and intensity every several minutes.

      In situ
      In situ
      In situ is a Latin phrase which translated literally as 'In position'. It is used in many different contexts.-Aerospace:In the aerospace industry, equipment on board aircraft must be tested in situ, or in place, to confirm everything functions properly as a system. Individually, each piece may...

       measurements, in real-time, can be taken by sending specially equipped reconnaissance flights into the cyclone. In the Atlantic basin, these flights are regularly flown by United States government hurricane hunters
      Hurricane Hunters
      The Hurricane Hunters are aircraft that fly into tropical cyclones in the North Atlantic Ocean and Northeastern Pacific Ocean for the specific purpose of directly measuring weather data in and around those storms. In the United States, the Air Force, Navy, and NOAA units have all participated in...

      . The aircraft used are WC-130 Hercules and WP-3D Orions, both four-engine turboprop
      Turboprop
      A turboprop engine is a type of turbine engine which drives an aircraft propeller using a reduction gear.The gas turbine is designed specifically for this application, with almost all of its output being used to drive the propeller...

       cargo aircraft. These aircraft fly directly into the cyclone and take direct and remote-sensing measurements. The aircraft also launch GPS dropsondes inside the cyclone. These sondes measure temperature, humidity, pressure, and especially winds between flight level and the ocean's surface. A new era in hurricane observation began when a remotely piloted Aerosonde
      Insitu Aerosonde
      The Aerosonde is a small unmanned aerial vehicle designed to collect weather data, including temperature, atmospheric pressure, humidity, and wind measurements, over oceans and remote areas. The Aerosonde was developed by Insitu, and is now manufactured by Aerosonde Ltd, which is a strategic...

      , a small drone aircraft, was flown through Tropical Storm Ophelia as it passed Virginia's Eastern Shore during the 2005 hurricane season. A similar mission was also completed successfully in the western Pacific ocean. This demonstrated a new way to probe the storms at low altitudes that human pilots seldom dare.


      Forecasting


      {{See also|Tropical cyclone track forecasting|Tropical cyclone prediction model|Tropical cyclone rainfall forecasting}}
      Because of the forces that affect tropical cyclone tracks, accurate track predictions depend on determining the position and strength of high- and low-pressure areas, and predicting how those areas will change during the life of a tropical system. The deep layer mean flow, or average wind through the depth of the troposphere
      Troposphere
      The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols....

      , is considered the best tool in determining track direction and speed. If storms are significantly sheared, use of wind speed measurements at a lower altitude, such as at the 700 hPa pressure surface (3000 metres (9,842.5 ft) above sea level) will produce better predictions. Tropical forecasters also consider smoothing out short-term wobbles of the storm as it allows them to determine a more accurate long-term trajectory. High-speed computers and sophisticated simulation software allow forecasters to produce computer models
      Tropical cyclone prediction model
      A tropical cyclone forecast model is a computer program that uses meteorological data to forecast aspects of the future state of tropical cyclones. There are three types of models: statistical, dynamical, or combined statistical-dynamic...

       that predict tropical cyclone tracks based on the future position and strength of high- and low-pressure systems. Combining forecast models with increased understanding of the forces that act on tropical cyclones, as well as with a wealth of data from Earth-orbiting satellites and other sensors, scientists have increased the accuracy of track forecasts over recent decades. However, scientists are not as skillful at predicting the intensity of tropical cyclones. The lack of improvement in intensity forecasting is attributed to the complexity of tropical systems and an incomplete understanding of factors that affect their development.

      Intensity classifications


      {{Main|Tropical cyclone scales}}

      Tropical cyclones are classified into three main groups, based on intensity: tropical depressions, tropical storms, and a third group of more intense storms, whose name depends on the region. For example, if a tropical storm in the Northwestern Pacific reaches hurricane-strength winds on the Beaufort scale
      Beaufort scale
      The Beaufort Scale is an empirical measure that relates wind speed to observed conditions at sea or on land. Its full name is the Beaufort Wind Force Scale.-History:...

      , it is referred to as a typhoon; if a tropical storm passes the same benchmark in the Northeast Pacific Basin
      Pacific hurricane
      A Pacific hurricane or tropical storm is a tropical cyclone that develops in the northeastern part of the Pacific Ocean. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, , central , and western...

      , or in the Atlantic
      Atlantic hurricane
      North Atlantic tropical cyclones usually form in the northern hemisphere summer or fall. Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph , while hurricanes have one-minute maximum sustained exceeding 74 mph...

      , it is called a hurricane. Neither "hurricane" nor "typhoon" is used in either the Southern Hemisphere or the Indian Ocean. In these basins
      Tropical cyclone basins
      Traditionally, areas of tropical cyclone formation are divided into seven basins. These include the north Atlantic Ocean, the eastern and western parts of the northern Pacific Ocean, the southwestern Pacific, the southwestern and southeastern Indian Oceans, and the northern Indian Ocean. The...

      , storms of tropical nature are referred to simply as "cyclones".

      As indicated in the table below, each basin uses a separate system of terminology
      Tropical cyclone scales
      Tropical systems are officially ranked on one of several tropical cyclone scales according to their maximum sustained winds and in what oceanic basin they are located...

      , making comparisons between different basins difficult. In the Pacific Ocean, hurricanes from the Central North Pacific sometimes cross the International Date Line
      International Date Line
      The International Date Line is a generally north-south imaginary line on the surface of the Earth, passing through the middle of the Pacific Ocean, that designates the place where each calendar day begins...

       into the Northwest Pacific, becoming typhoons (such as Hurricane/Typhoon Ioke
      Hurricane Ioke
      Hurricane Ioke was the strongest hurricane ever recorded in the Central Pacific...

       in 2006); on rare occasions, the reverse will occur. It should also be noted that typhoons with sustained winds greater than 67 metres per second (123.1 kn) or 150 miles per hour (241.4 km/h) are called Super Typhoons by the Joint Typhoon Warning Center.

      Tropical depression


      A tropical depression is an organized system of clouds and thunderstorms with a defined, closed surface circulation and maximum sustained wind
      Maximum sustained wind
      The maximum sustained winds associated with a tropical cyclone are a common indicator of the intensity of the storm. Within a mature tropical cyclone, they are found within the eyewall at a distance defined as the radius of maximum wind, or RMW. Unlike gusts, the value of these winds are...

      s of less than 17 metres per second (31.2 kn) or 38 miles per hour (61.2 km/h). It has no eye
      Eye (cyclone)
      The eye is a region of mostly calm weather found at the center of strong tropical cyclones. The eye of a storm is a roughly circular area and typically 30–65 km in diameter. It is surrounded by the eyewall, a ring of towering thunderstorms where the second most severe weather of a cyclone...

       and does not typically have the organization or the spiral shape of more powerful storms. However, it is already a low-pressure system, hence the name "depression". The practice of the Philippines
      Philippines
      The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

       is to name tropical depressions from their own naming convention when the depressions are within the Philippines' area of responsibility.

      Tropical storm


      A tropical storm is an organized system of strong thunderstorms with a defined surface circulation and maximum sustained winds between 17 metres per second (31.2 kn) (39 miles per hour (62.8 km/h)) and 32 metres per second (58.8 kn) (73 miles per hour (117.5 km/h)). At this point, the distinctive cyclonic shape starts to develop, although an eye is not usually present. Government weather services, other than the Philippines, first assign names to systems that reach this intensity (thus the term named storm).

      Hurricane or typhoon


      A hurricane or typhoon (sometimes simply referred to as a tropical cyclone, as opposed to a depression or storm) is a system with sustained winds of at least 33 metres per second (60.6 kn) or 74 miles per hour (119.1 km/h). A cyclone of this intensity tends to develop an eye, an area of relative calm (and lowest atmospheric pressure) at the center of circulation. The eye is often visible in satellite images as a small, circular, cloud-free spot. Surrounding the eye is the eyewall, an area about 16 kilometres (9.9 mi) to 80 kilometres (49.7 mi) wide in which the strongest thunderstorm
      Thunderstorm
      A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...

      s and winds circulate around the storm's center. Maximum sustained winds in the strongest tropical cyclones have been estimated at about 85 metres per second (156.1 kn) or 195 miles per hour (313.8 km/h).
      {{Tropical cyclone classification}}

      Origin of storm terms


      The word typhoon, which is used today in the Northwest Pacific, may be derived from Hindi/Urdu, Persian
      Persian language
      Persian is an Iranian language within the Indo-Iranian branch of the Indo-European languages. It is primarily spoken in Iran, Afghanistan, Tajikistan and countries which historically came under Persian influence...

       and Arabic
      Arabic language
      Arabic is a name applied to the descendants of the Classical Arabic language of the 6th century AD, used most prominently in the Quran, the Islamic Holy Book...

       ţūfān (طوفان), which in turn originates from Greek
      Greek language
      Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

       Typhon
      Typhon
      Typhon , also Typhoeus , Typhaon or Typhos was the last son of Gaia, fathered by Tartarus, and the most deadly monster of Greek mythology. He was known as the "Father of all monsters"; his wife Echidna was likewise the "Mother of All Monsters."Typhon was described in pseudo-Apollodorus,...

      (Τυφών), a monster from Greek mythology
      Greek mythology
      Greek mythology is the body of myths and legends belonging to the ancient Greeks, concerning their gods and heroes, the nature of the world, and the origins and significance of their own cult and ritual practices. They were a part of religion in ancient Greece...

       associated with storms. The related Portuguese
      Portuguese language
      Portuguese is a Romance language that arose in the medieval Kingdom of Galicia, nowadays Galicia and Northern Portugal. The southern part of the Kingdom of Galicia became independent as the County of Portugal in 1095...

       word tufão, used in Portuguese for typhoons, is also derived from Typhon. The word is also similar to Chinese "taifeng" ("toifung" in Cantonese
      Cantonese
      Cantonese is a dialect spoken primarily in south China.Cantonese may also refer to:* Yue Chinese, the Chinese language that includes Cantonese* Cantonese cuisine, the cuisine of Guangdong province...

      ) (颱風 – great winds), and also to the Japanese "taifu" (台風), which may explain why "typhoon" came to be used for East Asian cyclones.{{Citation needed|date=August 2009|reason=Sounds like a folk etymology.}}

      The word hurricane, used in the North Atlantic and Northeast Pacific, is derived from huracán, the Spanish word for the Carib/Taino
      Taíno people
      The Taínos were pre-Columbian inhabitants of the Bahamas, Greater Antilles, and the northern Lesser Antilles. It is thought that the seafaring Taínos are relatives of the Arawak people of South America...

       storm god, Juracán
      Juracán
      Juracán is the phonetic name given by the Spanish settlers to the god of chaos and disorder that the Taino Indians in Puerto Rico believed controlled the weather, particularly hurricanes. From this we derive the Spanish word huracán and eventually the English word hurricane...

      . This god is believed by scholars to have been at least partially derived from the Mayan
      Maya peoples
      The Maya people constitute a diverse range of the Native American people of southern Mexico and northern Central America. The overarching term "Maya" is a collective designation to include the peoples of the region who share some degree of cultural and linguistic heritage; however, the term...

       creator god, Huracan
      Huracan
      Huracan , in Mayan understandable as Jun Raqan "one legged", is a K'iche' Mayan god of wind, storm, fire and one of the creator deities who participated in all three attempts at creating humanity...

      . Huracan was believed by the Mayans to have created dry land out of the turbulent waters. The god was also credited with later destroying the "wooden people", the precursors to the "maize people
      Maya maize god
      Like other Mesoamerican peoples, the traditional Mayas recognize in their staple crop, the maize, a vital force with which they strongly identify. This is clearly shown by their mythological traditions. According to the 16th-century Popol Vuh, the Hero Twins have maize plants for alter egos and man...

      ", with an immense storm and flood. Huracan is also the source of the word orcan, another word for a particularly strong European windstorm
      European windstorm
      A European windstorm is a severe cyclonic windstorm associated with areas of low atmospheric pressure that track across the North Atlantic towards northwestern Europe. They are most common in the winter months...

      .

      Naming


      {{Main|Tropical cyclone naming|Lists of tropical cyclone names}}
      Storms reaching tropical storm strength were initially given names to eliminate confusion when there are multiple systems in any individual basin at the same time, which assists in warning people of the coming storm. In most cases, a tropical cyclone retains its name throughout its life; however, under special circumstances, tropical cyclones may be renamed while active. These names are taken from lists that vary from region to region and are usually drafted a few years ahead of time. The lists are decided on, depending on the regions, either by committees of the World Meteorological Organization
      World Meteorological Organization
      The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

       (called primarily to discuss many other issues) or by national weather offices involved in the forecasting of the storms. Each year, the names of particularly destructive storms (if there are any) are "retired" and new names are chosen to take their place. Different countries have different local conventions; for example, in Japan, storms are referred to by number (each year), such as 台風第9号 (Typhoon #9).

      Notable tropical cyclones


      {{Main|List of notable tropical cyclones|List of Atlantic hurricanes|List of Pacific hurricanes}}
      Tropical cyclones that cause extreme destruction are rare, although when they occur, they can cause great amounts of damage or thousands of fatalities.
      The 1970 Bhola cyclone
      1970 Bhola cyclone
      The 1970 Bhola cyclone was a devastating tropical cyclone that struck East Pakistan and India's West Bengal on November 12, 1970. It was the deadliest tropical cyclone ever recorded, and one of the deadliest natural disasters in modern times...

       is the deadliest tropical cyclone on record, killing more than 300,000 people and potentially as many as 1 million after striking the densely populated Ganges Delta
      Ganges Delta
      The Ganges Delta is a river delta in the South Asia region of Bengal, consisting of Bangladesh and the state of West Bengal, India. It is the world's largest delta, and empties into the Bay of Bengal...

       region of Bangladesh
      Bangladesh
      Bangladesh , officially the People's Republic of Bangladesh is a sovereign state located in South Asia. It is bordered by India on all sides except for a small border with Burma to the far southeast and by the Bay of Bengal to the south...

       on 13 November 1970. Its powerful storm surge was responsible for the high death toll. The North Indian cyclone basin has historically been the deadliest basin. Elsewhere, Typhoon Nina
      Typhoon Nina (1975)
      Super Typhoon Nina was a short-lived but intense super typhoon that caused catastrophic damage and loss of life in China after causing the Banqiao Dam to collapse...

       killed nearly 100,000 in China in 1975 due to a 100-year flood
      100-year flood
      A one-hundred-year flood is calculated to be the level of flood water expected to be equaled or exceeded every 100 years on average. The 100-year flood is more accurately referred to as the 1% annual exceedance probability flood, since it is a flood that has a 1% chance of being equaled or exceeded...

       that caused 62 dams including the Banqiao Dam
      Banqiao Dam
      The Banqiao Reservoir Dam is a dam on the River Ru in Zhumadian Prefecture, Henan province, China. It infamously failed in 1975, causing more casualties than any other dam failure in history, and was subsequently rebuilt....

       to fail. The Great Hurricane of 1780
      Great Hurricane of 1780
      The Great Hurricane of 1780, also known as Hurricane San Calixto, the Great Hurricane of the Antilles, and the 1780 Disaster, is the deadliest Atlantic hurricane on record. Over 20,000 people died when the storm passed through the Lesser Antilles in the Caribbean between October 10 and October...

       is the deadliest Atlantic hurricane
      Atlantic hurricane
      North Atlantic tropical cyclones usually form in the northern hemisphere summer or fall. Tropical cyclones can be categorized by intensity. Tropical storms have one-minute maximum sustained winds of at least 39 mph , while hurricanes have one-minute maximum sustained exceeding 74 mph...

       on record, killing about 22,000 people in the Lesser Antilles
      Lesser Antilles
      The Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...

      . A tropical cyclone does need not be particularly strong to cause memorable damage, primarily if the deaths are from rainfall or mudslides. Tropical Storm Thelma
      Tropical Storm Thelma
      Tropical Storm Thelma was the deadliest tropical storm of the 1991 Pacific typhoon season, killing between 5,101 to 8,100 people as it crossed the Philippines.-Meteorological history:A tropical disturbance developed over the eastern Caroline Islands in late October...

       in November 1991 killed thousands in the Philippines
      Philippines
      The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...

      , while in 1982, the unnamed tropical depression that eventually became Hurricane Paul killed around 1,000 people in Central America
      Central America
      Central America is the central geographic region of the Americas. It is the southernmost, isthmian portion of the North American continent, which connects with South America on the southeast. When considered part of the unified continental model, it is considered a subcontinent...

      .

      Hurricane Katrina
      Hurricane Katrina
      Hurricane Katrina of the 2005 Atlantic hurricane season was a powerful Atlantic hurricane. It is the costliest natural disaster, as well as one of the five deadliest hurricanes, in the history of the United States. Among recorded Atlantic hurricanes, it was the sixth strongest overall...

       is estimated as the costliest tropical cyclone worldwide, causing $81.2 billion in property damage (2008 USD) with overall damage estimates exceeding $100 billion (2005 USD). Katrina killed at least 1,836 people after striking Louisiana
      Louisiana
      Louisiana is a state located in the southern region of the United States of America. Its capital is Baton Rouge and largest city is New Orleans. Louisiana is the only state in the U.S. with political subdivisions termed parishes, which are local governments equivalent to counties...

       and Mississippi
      Mississippi
      Mississippi is a U.S. state located in the Southern United States. Jackson is the state capital and largest city. The name of the state derives from the Mississippi River, which flows along its western boundary, whose name comes from the Ojibwe word misi-ziibi...

       as a major hurricane
      Tropical cyclone scales
      Tropical systems are officially ranked on one of several tropical cyclone scales according to their maximum sustained winds and in what oceanic basin they are located...

       in August 2005. Hurricane Andrew
      Hurricane Andrew
      Hurricane Andrew was the third Category 5 hurricane to make landfall in the United States, after the Labor Day Hurricane of 1935 and Hurricane Camille in 1969. Andrew was the first named storm and only major hurricane of the otherwise inactive 1992 Atlantic hurricane season...

       is the second most destructive tropical cyclone in U.S history, with damages totaling $40.7 billion (2008 USD), and with damage costs at $31.5 billion (2008 USD), Hurricane Ike
      Hurricane Ike
      Hurricane Ike was the second-costliest hurricane ever to make landfall in the United States, the costliest hurricane ever to impact Cuba and the second most active hurricane to reach the Canadian mainland in the Great Lakes Region after Hurricane Hazel in 1954...

       is the third most destructive tropical cyclone in U.S history. The Galveston Hurricane of 1900
      Galveston Hurricane of 1900
      The Hurricane of 1900 made landfall on the city of Galveston in the U.S. state of Texas, on September 8, 1900.It had estimated winds of at landfall, making it a Category 4 storm on the Saffir-Simpson Hurricane Scale...

       is the deadliest natural disaster in the United States, killing an estimated 6,000 to 12,000 people in Galveston, Texas
      Galveston, Texas
      Galveston is a coastal city located on Galveston Island in the U.S. state of Texas. , the city had a total population of 47,743 within an area of...

      . Hurricane Mitch
      Hurricane Mitch
      Hurricane Mitch was the most powerful hurricane and the most destructive of the 1998 Atlantic hurricane season, with maximum sustained winds of 180 mph . The storm was the thirteenth tropical storm, ninth hurricane, and third major hurricane of the season. Along with Hurricane Georges, Mitch...

       caused more than 10,000 fatalities in Latin America. Hurricane Iniki
      Hurricane Iniki
      Hurricane Iniki was the most powerful hurricane to strike the U.S. state of Hawaii in recorded history. Forming on September 5 during the strong El Niño of 1991–1994, Iniki was one of eleven Central Pacific tropical cyclones during the 1992 season. It attained tropical storm status on...

       in 1992 was the most powerful storm to strike Hawaii
      Hawaii
      Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...

       in recorded history, hitting Kauai
      Kauai
      Kauai or Kauai, known as Tauai in the ancient Kaua'i dialect, is geologically the oldest of the main Hawaiian Islands. With an area of , it is the fourth largest of the main islands in the Hawaiian archipelago, and the 21st largest island in the United States. Known also as the "Garden Isle",...

       as a Category 4 hurricane, killing six people, and causing U.S. $3 billion in damage. Kauai was also struck by Hurricanes Dot (1959) and Iwa (1982) (see List of Hawaii hurricanes). Other destructive Eastern Pacific hurricane
      Pacific hurricane
      A Pacific hurricane or tropical storm is a tropical cyclone that develops in the northeastern part of the Pacific Ocean. For organizational purposes, the northern Pacific Ocean is divided into three regions: the eastern, , central , and western...

      s include Pauline
      Hurricane Pauline
      Hurricane Pauline was one of the strongest and deadliest Pacific hurricanes to make landfall on Mexico. The sixteenth tropical storm, eighth hurricane, and seventh major hurricane of the 1997 Pacific hurricane season, Pauline developed out of a tropical wave on October 5 about 250 miles ...

       and Kenna
      Hurricane Kenna
      Hurricane Kenna was the second-most intense Pacific hurricane to strike the west coast of Mexico in recorded history. Kenna was the sixteenth tropical depression, thirteenth tropical storm, seventh hurricane, sixth major hurricane, and third Category 5 hurricane of the 2002 Pacific hurricane season...

      , both causing severe damage after striking Mexico
      Mexico
      The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

       as major hurricanes. In March 2004, Cyclone Gafilo
      Cyclone Gafilo
      Cyclone Gafilo was a powerful tropical cyclone which struck Madagascar in March 2004, causing devastating damage. It is the most intense cyclone ever to form in the south-western Indian Ocean.-Meteorological history:...

       struck northeastern Madagascar
      Madagascar
      The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...

       as a powerful cyclone, killing 74, affecting more than 200,000, and becoming the worst cyclone to affect the nation for more than 20 years.


      The most intense storm on record was Typhoon Tip
      Typhoon Tip
      Typhoon Tip was the largest and most intense tropical cyclone on record. The nineteenth tropical storm and twelfth typhoon of the 1979 Pacific typhoon season, Tip developed out of a disturbance in the monsoon trough on October 4 near Pohnpei...

       in the northwestern Pacific Ocean in 1979, which reached a minimum pressure of 870 mbar (652.5 mmHg) and maximum sustained wind speeds of 165 knots (89.8 m/s) or 190 miles per hour (305.8 km/h). Tip
      Typhoon Tip
      Typhoon Tip was the largest and most intense tropical cyclone on record. The nineteenth tropical storm and twelfth typhoon of the 1979 Pacific typhoon season, Tip developed out of a disturbance in the monsoon trough on October 4 near Pohnpei...

      , however, does not solely hold the record for fastest sustained winds in a cyclone. Typhoon Keith in the Pacific and Hurricanes Camille
      Hurricane Camille
      Hurricane Camille was the third and strongest tropical cyclone and second hurricane during the 1969 Atlantic hurricane season. The second of three catastrophic Category 5 hurricanes to make landfall in the United States during the 20th century , which it did near the mouth of the Mississippi River...

       and Allen
      Hurricane Allen
      Hurricane Allen was the first and strongest hurricane of the 1980 Atlantic hurricane season. It was one of the strongest hurricanes in recorded history, one of the few hurricanes to reach Category 5 status on the Saffir-Simpson Hurricane Scale on three separate occasions, and spent more time...

       in the North Atlantic currently share this record with Tip. Camille was the only storm to actually strike land while at that intensity, making it, with 165 knots (89.8 m/s) or 190 miles per hour (305.8 km/h) sustained winds and 183 knots (99.6 m/s) or 210 miles per hour (338 km/h) gusts, the strongest tropical cyclone on record at landfall. Typhoon Nancy
      Typhoon Nancy (1961)
      Super Typhoon Nancy was a powerful tropical cyclone of the 1961 Pacific typhoon season. The system with possibly the strongest winds ever measured in a tropical cyclone, Nancy caused extensive damage and at least 173 deaths and thousands of injuries in Japan and elsewhere in September 1961...

       in 1961 had recorded wind speeds of 185 knots (100.7 m/s) or 215 miles per hour (346 km/h), but recent research indicates that wind speeds from the 1940s to the 1960s were gauged too high, and this is no longer considered the storm with the highest wind speeds on record. Likewise, a surface-level gust caused by Typhoon Paka
      Typhoon Paka
      Typhoon Paka was the last tropical cyclone in the 1997 Pacific Ocean hurricane and typhoon season, and was among the strongest Pacific typhoons in the month of December. Paka, which is the Hawaiian name for Pat, developed on November 28 from a trough well to the southwest of Hawaii...

       on Guam
      Guam
      Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...

       was recorded at 205 knots (111.6 m/s) or 235 miles per hour (378.2 km/h). Had it been confirmed, it would be the strongest non-tornadic
      Tornado
      A tornado is a violent, dangerous, rotating column of air that is in contact with both the surface of the earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. They are often referred to as a twister or a cyclone, although the word cyclone is used in meteorology in a wider...

       wind ever recorded on the Earth's surface, but the reading had to be discarded since the anemometer
      Anemometer
      An anemometer is a device for measuring wind speed, and is a common weather station instrument. The term is derived from the Greek word anemos, meaning wind, and is used to describe any airspeed measurement instrument used in meteorology or aerodynamics...

       was damaged by the storm. Hurricane Wilma
      Hurricane Wilma
      Hurricane Wilma was the most intense tropical cyclone ever recorded in the Atlantic basin. Wilma was the twenty-second storm , thirteenth hurricane, sixth major hurricane, and fourth Category 5 hurricane of the record-breaking 2005 season...

       is the most intense tropical cyclone in the Atlantic Basin and the strongest tropical cyclone in the Western Hemisphere.

      In addition to being the most intense tropical cyclone on record, Tip was the largest cyclone on record, with tropical storm-force winds 2170 kilometres (1,348.4 mi) in diameter. The smallest storm on record, Tropical Storm Marco
      Tropical Storm Marco (2008)
      Tropical Storm Marco was the smallest known tropical cyclone on record. The thirteenth named storm of the 2008 Atlantic hurricane season, Marco developed out of a broad area of low pressure over the northwestern Caribbean during late September 2008. Influenced by a tropical wave on October 4,...

      , formed during October 2008, and made landfall in Veracruz
      Veracruz
      Veracruz, formally Veracruz de Ignacio de la Llave officially Estado Libre y Soberano de Veracruz de Ignacio de la Llave , is one of the 31 states that, along with the Federal District, comprise the 32 federative entities of Mexico. It is divided in 212 municipalities and its capital city is...

      . Marco generated tropical storm-force winds only 37 kilometres (23 mi) in diameter.

      Hurricane John
      Hurricane John (1994)
      Hurricane John formed during the 1994 Pacific hurricane season and became both the longest-lasting and the farthest-traveling tropical cyclone ever observed...

       is the longest-lasting tropical cyclone on record, lasting 31 days in 1994
      1994 Pacific hurricane season
      The 1994 Pacific hurricane season officially started on May 15, 1994 in the eastern Pacific, and on June 1, 1994 in the central Pacific, and lasted until November 30, 1994. These dates conventionally delimit the period of each year when most tropical cyclones form in the northeastern Pacific Ocean...

      . Before the advent of satellite imagery in 1961, however, many tropical cyclones were underestimated in their durations. John is also the longest-tracked tropical cyclone in the Northern Hemisphere on record, which had a path of 7,165 miles (13,280 km). Reliable data for Southern Hemisphere cyclones is unavailable.

      Changes caused by El Niño-Southern Oscillation


      {{See also|El Niño-Southern Oscillation}}
      Most tropical cyclones form on the side of the subtropical ridge closer to the equator
      Equator
      An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

      , then move poleward past the ridge axis before recurving into the main belt of the Westerlies
      Westerlies
      The Westerlies, anti-trades, or Prevailing Westerlies, are the prevailing winds in the middle latitudes between 30 and 60 degrees latitude, blowing from the high pressure area in the horse latitudes towards the poles. These prevailing winds blow from the west to the east, and steer extratropical...

      . When the subtropical ridge
      Subtropical ridge
      The subtropical ridge is a significant belt of high pressure situated around the latitudes of 30°N in the Northern Hemisphere and 30°S in the Southern Hemisphere. It is characterized by mostly calm winds, which acts to reduce air quality under its axis by causing fog overnight, and haze during...

       position shifts due to El Niño, so will the preferred tropical cyclone tracks. Areas west of Japan
      Japan
      Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

       and Korea
      Korea
      Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

       tend to experience much fewer September–November tropical cyclone impacts during El Niño and neutral years. During El Niño years, the break in the subtropical ridge tends to lie near 130°E
      130th meridian east
      The meridian 130° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, Australia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole....

       which would favor the Japanese archipelago. During El Niño years, Guam
      Guam
      Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...

      's chance of a tropical cyclone impact is one-third of the long term average. The tropical Atlantic ocean experiences depressed activity due to increased vertical wind shear
      Wind shear
      Wind shear, sometimes referred to as windshear or wind gradient, is a difference in wind speed and direction over a relatively short distance in the atmosphere...

       across the region during El Niño years. During La Niña years, the formation of tropical cyclones, along with the subtropical ridge position, shifts westward across the western Pacific ocean, which increases the landfall threat to China
      China
      Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

      .

      Long-term activity trends

      {{See also|Atlantic hurricane reanalysis}}



      While the number of storms in the Atlantic has increased since 1995, there is no obvious global trend; the annual number of tropical cyclones worldwide remains about 87 ± 10 (Between 77 and 97 tropical cyclones annually). However, the ability of climatologists to make long-term data analysis in certain basins is limited by the lack of reliable historical data in some basins, primarily in the Southern Hemisphere. In spite of that, there is some evidence that the intensity of hurricanes is increasing. Kerry Emanuel
      Kerry Emanuel
      Kerry Emanuel is an American professor of meteorology currently working at the Massachusetts Institute of Technology in Cambridge. In particular he has specialized in atmospheric convection and the mechanisms acting to intensify hurricanes. He coined the term "hypercane" in 1994. In 2007, he was...

       stated, "Records of hurricane activity worldwide show an upswing of both the maximum wind speed in and the duration of hurricanes. The energy released by the average hurricane (again considering all hurricanes worldwide) seems to have increased by around 70% in the past 30 years or so, corresponding to about a 15% increase in the maximum wind speed and a 60% increase in storm lifetime."

      Atlantic storms are becoming more destructive financially, since five of the ten most expensive storms in United States history have occurred since 1990. According to the World Meteorological Organization
      World Meteorological Organization
      The World Meteorological Organization is an intergovernmental organization with a membership of 189 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...

      , “recent increase in societal impact from tropical cyclones has been caused largely by rising concentrations of population and infrastructure in coastal regions.” Pielke et al. (2008) normalized mainland U.S. hurricane damage from 1900–2005 to 2005 values and found no remaining trend of increasing absolute damage. The 1970s and 1980s were notable because of the extremely low amounts of damage compared to other decades. The decade 1996–2005 was the second most damaging among the past 11 decades, with only the decade 1926–1935 surpassing its costs. The most damaging single storm is the 1926 Miami hurricane
      1926 Miami Hurricane
      The 1926 Miami hurricane was a Category 4 hurricane that devastated Miami in September 1926. The storm also caused significant damage in the Florida Panhandle, the U.S. state of Alabama, and the Bahamas...

      , with $157 billion of normalized damage.

      Often in part because of the threat of hurricanes, many coastal regions had sparse population between major ports until the advent of automobile tourism; therefore, the most severe portions of hurricanes striking the coast may have gone unmeasured in some instances. The combined effects of ship destruction and remote landfall severely limit the number of intense hurricanes in the official record before the era of hurricane reconnaissance aircraft and satellite meteorology. Although the record shows a distinct increase in the number and strength of intense hurricanes, therefore, experts regard the early data as suspect.

      The number and strength of Atlantic hurricanes may undergo a 50–70 year cycle, also known as the Atlantic Multidecadal Oscillation
      Atlantic Multidecadal Oscillation
      The Atlantic multidecadal oscillation is a mode of variability occurring in the North Atlantic Ocean and which has its principal expression in the sea surface temperature field...

      . Nyberg et al. reconstructed Atlantic major hurricane activity back to the early 18th century and found five periods averaging 3–5 major hurricanes per year and lasting 40–60 years, and six other averaging 1.5–2.5 major hurricanes per year and lasting 10–20 years. These periods are associated with the Atlantic multidecadal oscillation. Throughout, a decadal oscillation related to solar irradiance was responsible for enhancing/dampening the number of major hurricanes by 1–2 per year.

      Although more common since 1995, few above-normal hurricane seasons occurred during 1970–94. Destructive hurricanes struck frequently from 1926–60, including many major New England hurricanes. Twenty-one Atlantic tropical storms formed in 1933
      1933 Atlantic hurricane season
      The 1933 Atlantic hurricane season was the second most active Atlantic hurricane season on record, with 21 storms forming during that year in the northwest Atlantic Ocean. The season ran through the summer and the first half of fall in 1933, and was surpassed in total number of tropical cyclones by...

      , a record only recently exceeded in 2005
      2005 Atlantic hurricane season
      The 2005 Atlantic hurricane season was the most active Atlantic hurricane season in recorded history, repeatedly shattering numerous records. The impact of the season was widespread and ruinous with an estimated 3,913 deaths and record damage of about $159.2 billion...

      , which saw 28 storms. Tropical hurricanes occurred infrequently during the seasons of 1900–25; however, many intense storms formed during 1870–99. During the 1887 season
      1887 Atlantic hurricane season
      Another May storm formed south of Jamaica on May 17, way outside of the season and moved generally northward. It crossed Cuba on the 19th as a tropical storm, and moved out to sea. Two peaked at twice, once on May 18 and May 20. Two dissipated on the 21st in the Atlantic Ocean...

      , 19 tropical storms formed, of which a record 4 occurred after 1 November and 11 strengthened into hurricanes. Few hurricanes occurred in the 1840s to 1860s; however, many struck in the early 19th century, including a 1821 storm
      1821 Norfolk and Long Island Hurricane
      The 1821 Norfolk and Long Island Hurricane was one of four known tropical cyclones that have made landfall in New York City. Another, even more intense hurricane struck the region in pre-Columbian times and was detected by paleotempestological research...

       that made a direct hit on New York City
      New York City
      New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

      . Some historical weather experts say these storms may have been as high as Category 4
      Saffir-Simpson Hurricane Scale
      The Saffir–Simpson Hurricane Scale , or the Saffir–Simpson Hurricane Wind Scale , classifies hurricanes — Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms — into five categories distinguished by the intensities of their sustained winds...

       in strength.

      These active hurricane seasons predated satellite coverage of the Atlantic basin. Before the satellite era began in 1960, tropical storms or hurricanes went undetected unless a reconnaissance aircraft encountered one, a ship reported a voyage through the storm, or a storm hit land in a populated area. The official record, therefore, could miss storms in which no ship experienced gale-force winds, recognized it as a tropical storm (as opposed to a high-latitude extra-tropical cyclone, a tropical wave, or a brief squall), returned to port, and reported the experience.

      Proxy records based on paleotempestological
      Paleotempestology
      Paleotempestology is the study of past tropical cyclone activity by means of geological proxies as well as historical documentary records. The term was coined by Kerry Emanuel.-Sedimentary proxy records:...

       research have revealed that major hurricane activity along the Gulf of Mexico
      Gulf of Mexico
      The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

       coast varies on timescales of centuries to millennia. Few major hurricanes struck the Gulf coast during 3000–1400 BC and again during the most recent millennium. These quiescent intervals were separated by a hyperactive period during 1400 BC and 1000 AD, when the Gulf coast was struck frequently by catastrophic hurricanes and their landfall probabilities increased by 3–5 times. This millennial-scale variability has been attributed to long-term shifts in the position of the Azores High
      Azores High
      The Azores High is a large subtropical semi-permanent centre of high atmospheric pressure found near the Azores in the Atlantic Ocean, at the Horse latitudes...

      , which may also be linked to changes in the strength of the North Atlantic Oscillation
      North Atlantic oscillation
      The North Atlantic oscillation is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. Through east-west oscillation motions of the Icelandic low and the Azores high, it controls the...

      .

      According to the Azores High hypothesis, an anti-phase pattern is expected to exist between the Gulf of Mexico coast and the Atlantic coast. During the quiescent periods, a more northeasterly position of the Azores High would result in more hurricanes being steered towards the Atlantic coast. During the hyperactive period, more hurricanes were steered towards the Gulf coast as the Azores High was shifted to a more southwesterly position near the Caribbean. Such a displacement of the Azores High is consistent with paleoclimatic evidence that shows an abrupt onset of a drier climate in Haiti
      Haiti
      Haiti , officially the Republic of Haiti , is a Caribbean country. It occupies the western, smaller portion of the island of Hispaniola, in the Greater Antillean archipelago, which it shares with the Dominican Republic. Ayiti was the indigenous Taíno or Amerindian name for the island...

       around 3200 14C
      Radiocarbon dating
      Radiocarbon dating is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 to estimate the age of carbon-bearing materials up to about 58,000 to 62,000 years. Raw, i.e. uncalibrated, radiocarbon ages are usually reported in radiocarbon years "Before Present" ,...

       years BP, and a change towards more humid conditions in the Great Plains
      Great Plains
      The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...

       during the late-Holocene as more moisture was pumped up the Mississippi Valley through the Gulf coast. Preliminary data from the northern Atlantic coast seem to support the Azores High hypothesis. A 3000-year proxy record from a coastal lake in Cape Cod
      Cape Cod
      Cape Cod, often referred to locally as simply the Cape, is a cape in the easternmost portion of the state of Massachusetts, in the Northeastern United States...

       suggests that hurricane activity increased significantly during the past 500–1000 years, just as the Gulf coast was amid a quiescent period of the last millennium.

      Global warming

      {{See also|Effects of global warming|Hurricane Katrina and global warming}}

      The U.S. National Oceanic and Atmospheric Administration
      National Oceanic and Atmospheric Administration
      The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...

       Geophysical Fluid Dynamics Laboratory
      Geophysical Fluid Dynamics Laboratory
      The Geophysical Fluid Dynamics Laboratory is a laboratory in the National Oceanic and Atmospheric Administration /Office of Oceanic and Atmospheric Research . The current director is Dr. V...

       performed a simulation to determine if there is a statistical
      Statistics
      Statistics is the study of the collection, organization, analysis, and interpretation of data. It deals with all aspects of this, including the planning of data collection in terms of the design of surveys and experiments....

       trend
      Periodic trends
      In Chemistry, periodic trends are the tendencies of certain elemental characteristics to increase or decrease as one progresses along a row or column of the periodic table of elements.-Atomic radius:...

       in the frequency or strength of tropical cyclones over time. The simulation concluded "the strongest hurricanes in the present climate may be upstaged by even more intense hurricanes over the next century as the earth's climate is warmed by increasing levels of greenhouse gases in the atmosphere".

      In an article in Nature
      Nature (journal)
      Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

      , Kerry Emanuel
      Kerry Emanuel
      Kerry Emanuel is an American professor of meteorology currently working at the Massachusetts Institute of Technology in Cambridge. In particular he has specialized in atmospheric convection and the mechanisms acting to intensify hurricanes. He coined the term "hypercane" in 1994. In 2007, he was...

       stated that potential hurricane destructiveness, a measure combining hurricane strength, duration, and frequency, "is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multidecadal oscillations in the North Atlantic and North Pacific, and global warming". Emanuel predicted "a substantial increase in hurricane-related losses in the twenty-first century". In more recent work published by Emanuel (in the March 2008 issue of the Bulletin of the American Meteorological Society), he states that new climate modeling data indicates “global warming should reduce the global frequency of hurricanes.” According to the Houston Chronicle, the new work suggests that, even in a dramatically warming world, hurricane frequency and intensity may not substantially rise during the next two centuries.

      Likewise, P.J. Webster and others published an article in Science
      Science (journal)
      Science is the academic journal of the American Association for the Advancement of Science and is one of the world's top scientific journals....

      examining the "changes in tropical cyclone number, duration, and intensity" over the past 35 years, the period when satellite data has been available. Their main finding was although the number of cyclones decreased throughout the planet excluding the north Atlantic Ocean
      Atlantic Ocean
      The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...

      , there was a great increase in the number and proportion of very strong cyclones.

      {{Costliest U.S. Atlantic hurricanes by wealth normalization|align=right}}
      The strength of the reported effect is surprising in light of modeling studies that predict only a one-half category increase in storm intensity as a result of a ~2 °C (3.6 °F) global warming. Such a response would have predicted only a ~10% increase in Emanuel's potential destructiveness index during the 20th century rather than the ~75–120% increase he reported. Second, after adjusting for changes in population and inflation, and despite a more than 100% increase in Emanuel's potential destructiveness index, no statistically significant increase in the monetary damages resulting from Atlantic hurricanes has been found.

      Sufficiently warm sea surface temperatures are considered vital to the development of tropical cyclones. Although neither study can directly link hurricanes with global warming, the increase in sea surface temperatures is believed to be due to both global warming and natural variability, e.g. the hypothesized Atlantic Multidecadal Oscillation
      Atlantic Multidecadal Oscillation
      The Atlantic multidecadal oscillation is a mode of variability occurring in the North Atlantic Ocean and which has its principal expression in the sea surface temperature field...

       (AMO), although an exact attribution has not been defined. However, recent temperatures are the warmest ever observed for many ocean basins.

      In February 2007, the United Nations
      United Nations
      The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

       Intergovernmental Panel on Climate Change
      Intergovernmental Panel on Climate Change
      The Intergovernmental Panel on Climate Change is a scientific intergovernmental body which provides comprehensive assessments of current scientific, technical and socio-economic information worldwide about the risk of climate change caused by human activity, its potential environmental and...

       released its fourth assessment report
      IPCC Fourth Assessment Report
      Climate Change 2007, the Fourth Assessment Report of the United Nations Intergovernmental Panel on Climate Change , is the fourth in a series of reports intended to assess scientific, technical and socio-economic information concerning climate change, its potential effects, and options for...

       on climate change
      Climate change
      Climate change is a significant and lasting change in the statistical distribution of weather patterns over periods ranging from decades to millions of years. It may be a change in average weather conditions or the distribution of events around that average...

      . The report noted many observed changes in the climate, including atmospheric composition, global average temperatures, ocean conditions, among others. The report concluded the observed increase in tropical cyclone intensity is larger than climate models predict. In addition, the report considered that it is likely that storm intensity will continue to increase through the 21st century, and declared it more likely than not that there has been some human contribution to the increases in tropical cyclone intensity. However, there is no universal agreement about the magnitude of the effects anthropogenic global warming has on tropical cyclone formation, track, and intensity. For example, critics such as Chris Landsea assert that man-made effects would be "quite tiny compared to the observed large natural hurricane variability". A statement by the American Meteorological Society
      American Meteorological Society
      The American Meteorological Society promotes the development and dissemination of information and education on the atmospheric and related oceanic and hydrologic sciences and the advancement of their professional applications. Founded in 1919, the American Meteorological Society has a membership...

       on 1 February 2007 stated that trends in tropical cyclone records offer "evidence both for and against the existence of a detectable anthropogenic signal" in tropical cyclogenesis
      Tropical cyclogenesis
      Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

      . Although many aspects of a link between tropical cyclones and global warming are still being "hotly debated", a point of agreement is that no individual tropical cyclone or season can be attributed to global warming. Research reported in the 3 September 2008 issue of Nature found that the strongest tropical cyclones are getting stronger, in particular over the North Atlantic and Indian oceans. Wind speeds for the strongest tropical storms increased from an average of 140 miles per hour (225.3 km/h) in 1981 to 156 miles per hour (251.1 km/h) in 2006, while the ocean temperature, averaged globally over the all regions where tropical cyclones form, increased from 28.2 °C (82.8 °F) to 28.5 °C (83.3 °F) during this period.

      Related cyclone types



      {{See also|Cyclone|Extratropical cyclone|Subtropical cyclone}}
      In addition to tropical cyclones, there are two other classes of cyclones within the spectrum of cyclone types. These kinds of cyclones, known as extratropical cyclone
      Extratropical cyclone
      Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth having neither tropical nor polar characteristics, and are connected with fronts and...

      s and subtropical cyclone
      Subtropical cyclone
      A subtropical cyclone is a weather system that has some characteristics of a tropical and an extratropical cyclone. As early as the 1950s, meteorologists were unclear whether they should be characterized as tropical or extratropical cyclones. They were officially recognized by the National...

      s, can be stages a tropical cyclone passes through during its formation
      Tropical cyclogenesis
      Tropical cyclogenesis is the term that describes the development and strengthening of a tropical cyclone in the atmosphere. The mechanisms through which tropical cyclogenesis occurs are distinctly different from those through which mid-latitude cyclogenesis occurs...

       or dissipation. An extratropical cyclone is a storm that derives energy from horizontal temperature differences, which are typical in higher latitudes. A tropical cyclone can become extratropical as it moves toward higher latitudes if its energy source changes from heat released by condensation to differences in temperature between air masses; although not as frequently, an extratropical cyclone can transform into a subtropical storm, and from there into a tropical cyclone. From space, extratropical storms have a characteristic "comma
      Comma (punctuation)
      The comma is a punctuation mark. It has the same shape as an apostrophe or single closing quotation mark in many typefaces, but it differs from them in being placed on the baseline of the text. Some typefaces render it as a small line, slightly curved or straight but inclined from the vertical, or...

      -shaped" cloud pattern. Extratropical cyclones can also be dangerous when their low-pressure centers cause powerful winds and high seas.

      A subtropical cyclone is a weather
      Weather
      Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...

       system that has some characteristics of a tropical cyclone and some characteristics of an extratropical cyclone. They can form in a wide band of latitude
      Latitude
      In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

      s, from the equator
      Equator
      An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

       to 50°. Although subtropical storms rarely have hurricane-force winds, they may become tropical in nature as their cores warm. From an operational standpoint, a tropical cyclone is usually not considered to become subtropical during its extratropical transition.

      Tropical cyclones in popular culture


      {{Main|Tropical cyclones in popular culture}}
      In popular culture
      Popular culture
      Popular culture is the totality of ideas, perspectives, attitudes, memes, images and other phenomena that are deemed preferred per an informal consensus within the mainstream of a given culture, especially Western culture of the early to mid 20th century and the emerging global mainstream of the...

      , tropical cyclones have made appearances in different types of media, including films, books, television, music, and electronic game
      Electronic game
      An electronic game is a game that employs electronics to create an interactive system with which a player can play. The most common form of electronic game today is the video game, and for this reason the terms are often mistakenly used synonymously. Other common forms of electronic game include...

      s. The media can have tropical cyclones that are entirely fiction
      Fiction
      Fiction is the form of any narrative or informative work that deals, in part or in whole, with information or events that are not factual, but rather, imaginary—that is, invented by the author. Although fiction describes a major branch of literary work, it may also refer to theatrical,...

      al, or can be based on real events. For example, George Rippey Stewart's Storm
      Storm (novel)
      Storm is a novel written by George Rippey Stewart and published in 1941. The book became a best-seller and helped lead to the naming of tropical cyclones worldwide, even though the main character of the book was an extratropical cyclone.-Plot summary:...

      , a best-seller published in 1941, is thought to have influenced meteorologists into giving female names to Pacific tropical cyclones. Another example is the hurricane in The Perfect Storm
      The Perfect Storm (film)
      The Perfect Storm is a 2000 dramatic disaster film directed by Wolfgang Petersen. It is an adaptation of the 1997 non-fiction book of the same title by Sebastian Junger about the crew of the Andrea Gail that got caught in the Perfect Storm of 1991. The film stars George Clooney, Mark Wahlberg,...

      , which describes the sinking of the Andrea Gail
      Andrea Gail
      The F/V Andrea Gail was a commercial fishing vessel that was lost at sea with all hands during the "Perfect Storm" of 1991. The vessel and her six-man crew had been fishing the North Atlantic Ocean out of Gloucester, Massachusetts. Her last reported position was northeast of Sable Island on...

      by the 1991 Perfect Storm. Also, hypothetical hurricanes have been featured in parts of the plots of series such as The Simpsons
      Hurricane Neddy
      "Hurricane Neddy" is the eighth episode of The Simpsons eighth season which originally aired December 29, 1996. It was written by Steve Young, directed by Bob Anderson and features a cameo by Jon Lovitz as Jay Sherman from The Critic. In this episode, "Hurricane Barbara" viciously strikes...

      , Invasion
      Invasion (TV series)
      Invasion is an American science fiction television series that aired on ABC for only one season beginning in September 2005. Somewhat similar to Invasion of the Body Snatchers, the show told the story of the aftermath of a hurricane in which water-based creatures infiltrate a small Florida town and...

      , Family Guy, Seinfeld
      The Checks
      "The Checks" is the 141st episode of the sitcom Seinfeld. This was the 7th episode for the 8th season. It aired on NBC on November 7, 1996.-Plot:...

      , Dawson's Creek
      Dawson's Creek
      Dawson's Creek is an American teen drama television series which debuted on January 20, 1998, on The WB Television Network and was produced by Sony Pictures Television. The show is set in the fictional seaside town of Capeside, Massachusetts, and in Boston, Massachusetts, during the later seasons...

      , and CSI: Miami
      CSI: Miami (season 2)
      The second season of CSI: Miami premiered on CBS on September 22, 2003 and ended May 24, 2004.-Notable cast members:-Episodes:...

      . The 2004 film The Day After Tomorrow
      The Day After Tomorrow
      The Day After Tomorrow is a 2004 American science-fiction disaster film that depicts the catastrophic effects of global warming in a series of extreme weather events that usher in global cooling which leads to a new ice age. The film did well at the box office, grossing $542,771,772 internationally...

      includes several mentions of actual tropical cyclones as well as featuring fantastical "hurricane-like" non-tropical Arctic storms.

      See also


      {{Portal|Tropical cyclones}}
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      • Cyclone
        Cyclone
        In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...

      • Disaster preparedness
      • HURDAT
        HURDAT
        The North Atlantic hurricane database, or HURDAT, is the database for all tropical cyclones in the Atlantic Ocean, Gulf of Mexico and Caribbean Sea, since 1851.-History:...

         (online database)
      • Hurricane Alley
        Hurricane Alley
        Hurricane Alley is an area of warm water in the Atlantic Ocean stretching from the west coast of northern Africa to the east coast of central America and Gulf Coast of the southern United States. Many hurricanes form within this area...

      • Saffir–Simpson Hurricane Scale

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      • Hypercane
        Hypercane
        A hypercane is a hypothetical class of extreme hurricane that could form if ocean temperatures reached around , which is warmer than the warmest ocean temperature ever recorded. Such an increase could be caused by a large asteroid or comet impact, a large volcanic, supervolcanic eruption, or very...

      • List of wettest tropical cyclones by country
      • Secondary flow in tropical cyclones

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      Annual seasons
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      Forecasting and preparation
      • Catastrophe modeling
        Catastrophe modeling
        Catastrophe modeling is the process of using computer-assisted calculations to estimate the losses that could be sustained due to a catastrophic event such as a hurricane or earthquake...

      • Hurricane engineering
        Hurricane engineering
        Hurricane engineering is a specialist sub-discipline of civil engineering that encompasses planning, analysis, design, response, and recovery of civil engineering systems and infrastructure for hurricane hazards. Hurricane engineering is a relatively new and emerging discipline within the field of...

      • Hurricane preparedness
        Hurricane preparedness
        Hurricane preparedness encompasses the actions and planning taken before a tropical cyclone strikes to mitigate damage and injury from the storm...

      • Hurricane-proof building
        Hurricane-proof building
        Tornadoes, cyclones, and other strong winds damage or destroy many buildings. However, with proper design and construction, the damage to buildings by these forces can be greatly reduced. A variety of methods can help a building survive strong winds and storm surge....

      • Tropical cyclone watches and warnings

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      External links


      {{Wiktionary}}
      {{Commons category|Tropical cyclones}}

      Regional Specialized Meteorological Centers

      Tropical Cyclone Warning Centers

      Reference

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      {{Cyclones}}

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