Tropical systemsA tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air...
are officially ranked on one of several
tropical cyclone scales according to their maximum sustained winds and in what
oceanic basinTraditionally, areas of tropical cyclone formation are divided into seven basins. These include the north Atlantic Ocean, the eastern and western parts of the Pacific Ocean , the southwestern Pacific, the southwestern and southeastern Indian Oceans, and the northern Indian Ocean...
they are located. Only a few scales of classifications are used officially by the meteorological agencies monitoring the tropical cyclones, but some alternative scales also exist, such as Accumulated Cyclone Energy, the Power Dissipation Index, the Integrated Kinetic Energy Index, and Hurricane Severity Index.
Should a tropical cyclone form in the
North Atlantic OceanThe Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres , it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek...
or the Northeastern
Pacific OceanThe Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Tepre Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan. It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and...
, it will be classified using one of the categories in the
Saffir-Simpson Hurricane ScaleThe Saffir–Simpson Hurricane Scale is a classification used for most Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms. The scale divides hurricanes into five categories distinguished by the intensities of their sustained winds...
. In the Western Pacific, tropical cyclones will be ranked using the
Japan Meteorological AgencyThe 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...
's scale. The
Regional Specialized Meteorological CentreA 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...
{RSMC} in
New DelhiNew Delhi is the capital of India. It is situated within the metropolis of Delhi and serves as the seat of the Government of India and the Government of the National Capital Territory of Delhi....
,
IndiaIndia, officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
also uses a different scale to assess the maximum sustained winds of a tropical cyclone. In the
Southern HemisphereThe Southern Hemisphere is the half of a planet that is south of the equator—the word hemisphere literally means 'half ball'...
, the
Météo-FranceMétéo-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...
forecast center on
La ReunionRéunion is an island located in the Indian Ocean, east of Madagascar, about south west of Mauritius, the nearest island.Administratively, Réunion is one of the overseas départements of France...
uses a scale that covers the whole of the South West Indian Ocean. Both the Australian Bureau of Meteorology and the RSMC in Nadi, Fiji use the Australian tropical cyclone intensity scale.
The definition of
sustained windsThe 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...
recommended by the
World Meteorological OrganizationThe World Meteorological Organization is an intergovernmental organization with a membership of 188 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...
(WMO) and used by most weather agencies is that of a 10-minute average at a height of 10
mThe metre or meter is the basic unit of length in the International System of Units . Historically, the metre was defined by the French Academy of Sciences as the length between two marks on a platinum-iridium bar, which was designed to represent one ten-millionth of the distance from the Equator...
(33 ft). However, the Saffir-Simpson Hurricane Scale is based on wind speed measurements averaged over a 1-minute period, at 10 m (33 ft) above the surface. The scale used by RSMC New Delhi applies a 3-minute averaging period, and the Australian scale is based on both 3-second wind gusts and maximum sustained winds averaged over a 10-minute interval. These make direct comparisons between basins difficult.
Atlantic and East Pacific
The
Saffir-Simpson Hurricane ScaleThe Saffir–Simpson Hurricane Scale is a classification used for most Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms. The scale divides hurricanes into five categories distinguished by the intensities of their sustained winds...
is the classification system used for tropical cyclones in the
Atlantic OceanThe Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about 106.4 million square kilometres , it covers approximately one-fifth of the Earth's surface and about one-quarter of its water surface area. The first part of its name refers to the Atlas of Greek...
and in the
Pacific OceanThe Pacific Ocean is the largest of the Earth's oceanic divisions. Its name is derived from the Latin name Tepre Pacificum, "peaceful sea", bestowed upon it by the Portuguese explorer Ferdinand Magellan. It extends from the Arctic in the north to Antarctica in the south, bounded by Asia and...
east of the
antimeridianThe 180th meridian or antimeridian is the meridian which is 180° east or west of the Prime Meridian passing through the Royal Observatory, Greenwich. It is common to both east longitude and west longitude. It is used as the basis for the International Date Line because it for the most part passes...
. In these oceanic basins, tropical cyclones with
maximum sustained windThe 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 below 34
knThe knot is a unit of speed equal to one nautical mile per hour, which is equal to exactly 1.852 km/h and approximately 1.151 mph. The abbreviation kn is preferred by American and Canadian maritime authorities, and by the Institute of Electrical and Electronics Engineers; however, the...
(65
km/hThe kilometre per hour is a unit of speed or velocity, expressing the number of kilometers traveled in one hour...
, 39
mphThe mile per hour is a unit of speed, measured in Imperial units expressing the number of international miles covered per hour.It is currently the unit used for speed limits, and speeds, on roads in the United Kingdom and United States...
) are labeled as
tropical depressions by either the
National Hurricane CenterThe National Hurricane Center , located at Florida International University in Miami, Florida, is the division of National Weather Service's Tropical Prediction Center responsible for tracking and predicting the likely behavior of tropical depressions, tropical storms and hurricanes.When tropical...
(if it is in the North Atlantic or Northeast Pacific Basin) or the
Central Pacific Hurricane CenterThe 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...
(if located in the North Central Pacific Ocean). Should a tropical depression should reach 35 kn (65 km/h, 40 mph), it will
receive a namePresently, most tropical cyclones are given a name using one of several lists of tropical cyclone names. Storms of tropical storm strength are given names to allow the public to easily distinguish between systems when there are multiple systems in an individual basin at the same time...
and will be classified as a
tropical storm. If the tropical storm continues to intensify and reaches maximum sustained winds of 64 kn (119 km/h, 74 mph) then the tropical storm will be designated as a
hurricane.
The Saffir-Simpson scale counts with five different classifications for the intensity of a hurricane, with a Category 1 storm having the lowest maximum winds, whilst a Category 5 hurricane having the highest. Storms that meet the 64-knot threshold, but do not possess maximum sustained winds in excess of 83 kn (177 km/h, 96 mph) are classified as Category 1 hurricanes. A Category 1 storm will be upgraded to a Category 2 hurricane if its maximum sustained winds reach 83 knots. Tropical cyclones that possess wind speeds of at least 96 kn (178 km/h, 111 mph) are classified as Category 3 hurricanes. Category 3 also marks the point at which the NHC and CPHC classify strong storms as
major hurricanes. If a hurricane's maximum sustained winds reach 114 kn, (210 km/h, 131 mph), it will be catalogued as a Category 4 hurricane. Storms with winds that surpass 136 kn (250 km/h, 156 mph) are of Category 5 intensity.
Although increasing echelons of the scale correspond to stronger winds, the rankings are not absolute in terms of effects. Lower-category storms can inflict greater damage than higher-category storms, depending on factors such as local terrain, population density and total rainfall. For instance, a Category 2 that strikes a major urban area will likely do more damage than a large Category 5 hurricane that strikes a mostly rural region. In fact, tropical systems of less than hurricane strength can produce significant damage and human casualties, especially from flooding and landslides.
Historically, the term
great hurricane was used to describe storms that possessed winds of at least 110 kn (200 km/h, 125 mph), large radii (over 100 mi / 160
kmThe kilometre , symbol km is a unit of length in the metric system, equal to one thousand metres and is therefore exactly equal to the distance travelled by light in free space in of a second....
) and that caused large amounts of destruction. This term fell into disuse after the introduction of the Saffir-Simpson scale in the early 1970s.
West Pacific
Any tropical cyclone that forms to the west of
180°The 180th meridian or antimeridian is the meridian which is 180° east or west of the Prime Meridian passing through the Royal Observatory, Greenwich. It is common to both east longitude and west longitude. It is used as the basis for the International Date Line because it for the most part passes...
and east of
100°EThe meridian 100° east of Greenwich is a line of longitude that extends from the North Pole across the Arctic Ocean, Asia, the Indian Ocean, the Southern Ocean, and Antarctica to the South Pole....
in the Northern Hemisphere is officially monitored by the
Regional Specialized Meteorological CenterA 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...
in
Tokyo, officially , is one of the 47 prefectures of Japan and is located on the eastern side of the main island Honshū. The twenty-three special wards of Tokyo, each governed as a city, cover the area that was once the city of Tokyo in the eastern part of the prefecture, totaling over 8 million people....
,
Japanis an island country in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, People's Republic of 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...
. The
Japan Meteorological AgencyThe 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...
, which runs RSMC Tokyo, uses four different categories to measure the wind speed produced by a tropical cyclone. These classifications are based on the
maximum sustained windThe 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 produced by the storm averaged over a 10-minute interval.
A
tropical depression is the lowest category that the
Japan Meteorological AgencyThe 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...
uses and is the term used for a tropical system that has wind speeds not exceeding 35 knots, (40 mph, 65 km/h). A tropical depression is upgraded to a
tropical storm should its sustained wind speeds exceed 35 knots, (40 mph, 65 km/h). Tropical storms also receive official names from RSMC Tokyo. Should the storm intensify further and reach sustained wind speeds of 50 knot (60 mph, 95 km/h) then it will be classified as a
severe tropical storm. Once the system's maximum sustained winds reach wind speeds of 65 knots (70 mph 120 km/h), the JMA will designate the tropical cyclone as a
typhoon—the highest category on its scale. From 2009 the Hong Kong observatory started to further divide typhoon into two further classifications
severe typhoon and
super typhoon. A severe typhoon has winds off at least 80 knot (95 mph, 150 km/h) whilst a super typhoon has winds of at least 100 knot (115 mph, 185 km/h).
The
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
'
Joint Typhoon Warning CenterThe Joint Typhoon Warning Center is a joint United States Navy – United States Air Force task force located at Naval Maritime Forecast Center in Pearl Harbor, Hawaii. The JTWC is responsible for the issuing of tropical cyclone warnings in the North West Pacific Ocean, South Pacific Ocean and...
(JTWC) unofficially classifies typhoons with wind speeds of at least 130 knots (67 m/s; 150 mph; 241 km/h)—the equivalent of a strong Category 4 storm in the
Saffir-Simpson scaleThe Saffir–Simpson Hurricane Scale is a classification used for most Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms. The scale divides hurricanes into five categories distinguished by the intensities of their sustained winds...
—as
super typhoons. However, the maximum sustained wind speed measurements that the JTWC uses are based on a 1-minute averaging period, akin to the U.S.'
National Hurricane CenterThe National Hurricane Center , located at Florida International University in Miami, Florida, is the division of National Weather Service's Tropical Prediction Center responsible for tracking and predicting the likely behavior of tropical depressions, tropical storms and hurricanes.When tropical...
and
Central Pacific Hurricane CenterThe 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...
. As a result, the JTWC's wind reports are higher than JMA's measurements, as the latter are based on a 10-minute averaging interval.
North Indian Ocean
Any tropical cyclone that forms between
longitudeLongitude , identified by the Greek letter lambda , is the geographic coordinate most commonly used in cartography and global navigation for east-west measurement...
45°E and 100°E in the
Northern HemisphereThe Northern Hemisphere is the half of a planet that is north of the equator—the word hemisphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator...
is monitored by the
India Meteorological DepartmentThe India Meteorological Department , also referred to as the Met Office, is a Government of India organisation that is responsible for meteorological observations, weather forecasts, and detecting earthquakes. The IMD is also the Regional Specialized Meteorological Center responsible for...
(IMD), who run the
Regional Specialized Meteorological CenterA 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...
in
New DelhiNew Delhi is the capital of India. It is situated within the metropolis of Delhi and serves as the seat of the Government of India and the Government of the National Capital Territory of Delhi....
,
IndiaIndia, officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the south, the Arabian Sea on the west, and the Bay of Bengal...
. Since 1998, RSMC New Delhi has used six different categories to measure the wind speed of a
tropical cycloneA tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air...
based on the
maximum sustained windThe 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 over a 3-minute averaging period.
A
depression is the lowest category that RSMC New Delhi uses to designate tropical systems, and systems designated as depressions have wind speeds of under 27 kn (51 km/h, 31 mph). A depression is classified as a
deep depression when it has maximum sustained winds between 27 kn (51 km/h, 31 mph) and 33 kn (61 km/h, 38 mph). Should a deep depression intensify further, it will be classified as a
cyclonic storm if its sustained winds reach 34 kn (62 km/h, 39 mph). When a tropical system is classified as a cyclonic storm, it is
assigned a namePresently, most tropical cyclones are given a name using one of several lists of tropical cyclone names. Storms of tropical storm strength are given names to allow the public to easily distinguish between systems when there are multiple systems in an individual basin at the same time...
by the IMD.
In cases where cyclonic storms possess wind speeds greater than 48 kn, (88 km/h, 55 mph), they are classified as
severe cyclonic storms. A severe cyclonic storm is labeled as a
very severe cyclonic storm when it reaches wind speeds greater than 64 kn, (118 km/h, 74 mph). Finally, a
super cyclonic storm is the highest category that the India Meteorological Department uses in its scale, and is used to refer to tropical cyclones that have maximum sustained winds exceeding 120 kn, (222 km/h, 138 mph).
Prior to 1988, cyclones were classified into 4 categories which were depression, deep depression, cyclonic storms and severe cyclonic storms. However in 1988 the IMD started to rate cyclones with wind speeds of more than 64 kn, (118 km/h, 74 mph) as severe cyclonic storms. The IMD then made another change in 1998 to introduce a category for super cyclonic storms which are cyclonic storms with wind speeds of more than 120 kn, (222 km/h, 138 mph).
Southwest Indian Ocean
Any Tropical Cyclone that forms to the west of 90°E in the Southern Hemisphere, is monitored by Météo-France who run the
Regional Specialized Meteorological CenterA 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...
in
La ReunionLa Reunion may refer to:*La Reunion , a communal settlement near present-day Dallas, Texas*La Réunion, Lot-et-Garonne, a town in the Lot-et-Garonne department of France*La Reunión , a 2007 album by reggaeton duo Yaga & Mackie...
. RSMC La Reunion uses seven different categories to measure the wind speed of a tropical cyclone. It is based on a 10-minute average maximum sustained winds, rather than 1-Minute Maximum Sustained winds which is what the
Saffir-Simpson Hurricane ScaleThe Saffir–Simpson Hurricane Scale is a classification used for most Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms. The scale divides hurricanes into five categories distinguished by the intensities of their sustained winds...
uses.
A Tropical Disturbance is the lowest category on the Southwest Indian Ocean Tropical Cyclone scale, and has wind speeds 28 knots (32 mph, 50 km/h). A Tropical Disturbance is designated as a Tropical Depression, when the disturbance reaches wind speeds above 28 knots (32 mph, 50 km/h). Should a Tropical Depression reach wind speeds of 35 knots (40 mph, 65 km/h.) then it will be classified as a Moderate Tropical Storm and assigned a name by either the Sub Regional Center in
MauritiusMauritius , officially the Republic of Mauritius, is an island nation off the coast of the African continent in the southwest Indian Ocean, about east of Madagascar. In addition to the island of Mauritius, the Republic includes the islands of Cargados Carajos, Rodrigues and the Agalega Islands...
or
MadagascarMadagascar, or Republic of Madagascar , is an island nation in the Indian Ocean off the southeastern coast of Africa. The main island, also called Madagascar, is the fourth-largest island in the world, and is home to 5% of the world's plant and animal species, of which more than 80% are endemic to...
.
Should the named storm intensify further and reach winds speeds of 48 knots (55 mph, 89 km/h), then it will be classified as a Severe Tropical Storm. A Severe Tropical Storm is designated as a
Tropical CycloneA tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air...
when it reaches wind speeds of 64 knots (74 mph, 118 km/h). Should a Tropical Cyclone intensify further and reach wind speeds of 90 knots (103 mph, 166 km/h), it will be classified as an Intense Tropical Cyclone. A Very Intense Tropical Cyclone is the highest category on the Southwest Indian Ocean Tropical Cyclone scale, and has winds of over 115 knots (132 mph 212 km/h).
Australia
Any
Tropical CycloneA tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air...
that forms to the east of 90°E in the
Southern HemisphereThe Southern Hemisphere is the half of a planet that is south of the equator—the word hemisphere literally means 'half ball'...
, is monitored by either the Australian Bureau of Meteorology and or the
Regional Specialized Meteorological CenterA 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...
in Nadi, Fiji. Both warning centers use the Australian tropical cyclone intensity scale which measures tropical cyclones using a six category system. It is based on estimated maximum wind
gustsWind is the flow of air or other gases that compose an atmosphere . On Earth, wind consists of the bulk movement of air...
, which are a further 30-40% stronger than the 10-minute average sustained winds. This is different than the
Saffir-Simpson Hurricane ScaleThe Saffir–Simpson Hurricane Scale is a classification used for most Western Hemisphere tropical cyclones that exceed the intensities of tropical depressions and tropical storms. The scale divides hurricanes into five categories distinguished by the intensities of their sustained winds...
which uses 1-Minute Maximum Sustained winds.
When a Tropical Cyclone that has wind speeds below 35 knots (40 mph, 65 km/h) forms east of 160°E it is labeled as either a Tropical Disturbance or a Tropical Depression by RSMC Nadi. If it forms to the west of 160°E it is labeled as a Tropical Low by the Australian Bureau of Meteorology. However if it forms to the north of 10°S and between 90°E to 125°E the low is labeled as a Tropical Depression by the Tropical Cyclone Warning Center in
JakartaJakarta is the capital and largest city of Indonesia. It also has a greater population than any other city in Southeast Asia. It was formerly known as Sunda Kelapa , Jayakarta , Batavia , and Djakarta . Located on the northwest coast of Java, it has an area of and a population of 8,489,910...
,
IndonesiaThe Republic of Indonesia is a country in Southeast Asia and Oceania. Indonesia comprises 17,508 islands. With an estimated population of around 237 million people, it is the world's fourth most populous country, with the world's largest population of Muslims.Indonesia is a republic, with an...
.
If a tropical depression should reach 35 knots (40 mph, 65 km/h), it will be named by the TCWC or RSMC and be classified as a
Tropical CycloneA tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air...
. Should the cyclone intensify further reaching maximum sustained winds of 65 knots (75 mph 145 km/h) then the cyclone will be designated as a Category Three Severe Tropical Cyclone. A Severe Tropical Cyclone will be classified as a Category Five Severe Tropical Cyclone should the cyclones maximum sustained wind speeds be greater than 110 Knots (130 mph, 200 km/h) and the gusts be above 150 knots (175 mph, 280 km/h).
Comparisons across basins
The terminology for tropical cyclones differs from one region to another. Below is a summary of the classifications used by
Regional Specialized Meteorological CentersA 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...
worldwide:
| Tropical Cyclone Classifications (all winds are 10-minute averages) |
|
! Beaufort scaleThe Beaufort scale is an empirical measure for describing wind speed based mainly on observed sea conditions. Its full name is the Beaufort wind force scale.-History:...
! 10-minute sustained winds (knotsThe knot is a unit of speed equal to one nautical mile per hour, which is equal to exactly 1.852 km/h and approximately 1.151 mph. The abbreviation kn is preferred by American and Canadian maritime authorities, and by the Institute of Electrical and Electronics Engineers; however, the...
)
! N Indian Ocean
IMD
! SW Indian Ocean
MFMétéo-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...
! Australia
BOM
! SW Pacific
FMSThe Fiji Meteorological Service is a Department of the government of Fiji responsible for providing weather forecasting and is based in Nadi. Since 1995, the FMS has been responsible for the forecasting of tropical cyclones for much of the south Pacific Ocean...
! NW Pacific
JMAThe 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...
! NW Pacific
JTWCThe Joint Typhoon Warning Center is a joint United States Navy – United States Air Force task force located at Naval Maritime Forecast Center in Pearl Harbor, Hawaii. The JTWC is responsible for the issuing of tropical cyclone warnings in the North West Pacific Ocean, South Pacific Ocean and...
! NE Pacific &
N Atlantic
NHCThe National Hurricane Center , located at Florida International University in Miami, Florida, is the division of National Weather Service's Tropical Prediction Center responsible for tracking and predicting the likely behavior of tropical depressions, tropical storms and hurricanes.When tropical...
& CPHCThe 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...
>
| 0–6 |
<28 |
Depression |
Tropical Disturbance |
Tropical Low |
Tropical Depression |
Tropical Depression |
Tropical Depression |
Tropical Depression |
| 7 |
28-29 |
Deep Depression |
Tropical Depression |
| 30-33 |
| 8–9 |
34–47 |
Cyclonic Storm |
Moderate Tropical Storm |
Tropical Cyclone (1) |
Tropical Cyclone (1) |
Tropical Storm |
Tropical Storm |
Tropical Storm |
| 10 |
48–55 |
Severe Cyclonic Storm |
Severe Tropical Storm |
Tropical Cyclone (2) |
Tropical Cyclone (2) |
Severe Tropical Storm |
| 11 |
56–63 |
| 12 |
64–72 |
Very Severe Cyclonic Storm |
Tropical Cyclone |
Severe Tropical Cyclone (3) |
Severe Tropical Cyclone (3) |
Typhoon |
Typhoon |
Hurricane (1) |
| 13 |
73–85 |
Hurricane (2) |
| 14 |
86–89 |
Severe Tropical Cyclone (4) |
Severe Tropical Cyclone (4) |
Major Hurricane (3) |
| 15 |
90–99 |
Intense Tropical Cyclone |
| 16 |
100–106 |
Major Hurricane (4) |
| 17 |
107-114 |
Severe Tropical Cyclone (5) |
Severe Tropical Cyclone (5) |
| 115–119 |
Very Intense Tropical Cyclone |
Super Typhoon |
| >120 |
Super Cyclonic Storm |
Major Hurricane (5) |
Alternative scales
There are other scales that are not officially used by any of the
Regional Specialized Meteorological CentreA 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 or the Tropical Cyclone Warning Centres. However they are used by other organizations, such as the
National Oceanic and Atmospheric AdministrationThe National Oceanic and Atmospheric Administration is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...
. An example of such scale is the Integrated Kinetic Energy index, which measures the destructive potential of the storm surge; it works on a scale that ranges from one to six, with six having the highest destructive potential.
Accumulated Cyclone EnergyAccumulated cyclone energy is a measure used by the National Oceanic and Atmospheric Administration to express the activity of individual tropical cyclones and entire tropical cyclone seasons, particularly the North Atlantic hurricane season. It uses an approximation of the energy used by a...
(ACE), is used by the National Oceanic and Atmospheric Administration and other agencies, to express the activity of individual tropical cyclones which are above tropical storm strength and entire tropical cyclone seasons. It is calculated by taking the squares of the estimated maximum sustained velocity of every active tropical storm (wind speed 35 knots or higher), at six-hour intervals. The numbers are usually divided by 10,000 to make them more manageable. The unit of ACE is 10
4 kt
2, and for use as an index the unit is assumed. As well as being squared ACE can also be cubed, and this version is known as the Power Dissipation Index (PDI).
The
Hurricane Severity IndexThe Hurricane Severity Index is an enhanced hurricane rating system which more accurately defines the strength and destructive capability of a given storm than other scales currently utilized. The HSI uses comprehensive equations which incorporate not only the intensity of the winds but the size...
(HSI) is another scale used and rates the severity of all types of tropical and subtropical cyclones based on both the intensity and the size of their wind fields. The HSI is a 0 to 50 point scale, allotting up to 25 points for a
Tropical cyclone'sA tropical cyclone is a storm system characterized by a large low-pressure center and numerous thunderstorms that produce strong winds and heavy rain. Tropical cyclones feed on heat released when moist air rises, resulting in condensation of water vapor contained in the moist air...
intensity and up to 25 points for wind field size. Points are awarded on an exponential scale, with the majority of points reserved for hurricane force and greater wind fields.
Wind speed conversions
The definition of
sustained windsThe 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...
recommended by the
World Meteorological OrganizationThe World Meteorological Organization is an intergovernmental organization with a membership of 188 Member States and Territories. It originated from the International Meteorological Organization , which was founded in 1873...
(WMO) and used by most weather agencies is that of a 10-minute average at a height of 10
mThe metre or meter is the basic unit of length in the International System of Units . Historically, the metre was defined by the French Academy of Sciences as the length between two marks on a platinum-iridium bar, which was designed to represent one ten-millionth of the distance from the Equator...
(33 ft). However RSMC Miami and Honolulu, as well as the Joint Typhoon Warning Center, define sustained winds based on 1-minute average speed, and are also measured 10 m (33 ft) above the surface. To convert a one-minute wind speed from a tropical cyclone to a ten minute wind speed, the 1 minute speed has to be multiplied by 0.88. While a ten minute wind speed has to be multiplied by 1.14 to get a 1 minute wind speed.
See also
- Tropical cyclogenesis
Tropical cyclogenesis is the technical term describing 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...
- 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 Pacific Ocean , the southwestern Pacific, the southwestern and southeastern Indian Oceans, and the northern Indian Ocean...
- Tropical cyclone naming
Presently, most tropical cyclones are given a name using one of several lists of tropical cyclone names. Storms of tropical storm strength are given names to allow the public to easily distinguish between systems when there are multiple systems in an individual basin at the same time...
External links
Regional Specialized Meteorological Centres
- US National Hurricane Center – North Atlantic, Eastern Pacific
- Central Pacific Hurricane Center – Central Pacific
- Japan Meteorological Agency – NW Pacific
- India Meteorological Department – Bay of Bengal
The Bay of Bengal IPA:ˈbɒŋɡopoʃɑːˈgoɽ), the largest bay of the world, forms the northeastern part of the Indian Ocean. It resembles a triangle in shape, and is bordered by Bangladesh and the Indian state of West Bengal to the north , India and Sri Lanka to the west and Myanmar and the Andaman and...
and the Arabian SeaThe Arabian Sea is a region of the Indian Ocean bounded on the east by India, on the north by Pakistan and Iran, on the west by Arabian Peninsula, on the south, approximately, by a line between Cape Guardafui, the north-east point of Somalia, Socotra, Kanyakumari in India, and the western coast...
- Japan Meteorological Agency – NW Pacific
- Météo-France – La Reunion – South Indian Ocean from 30°E to 90°E
- Fiji Meteorological Service – South Pacific west of 160°E, north of 25° S
Tropical Cyclone Warning Centers