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Dvorak technique

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**Dvorak T-Number and Corresponding Intensity**
T-Number	Winds (knots Knot (speed) The knot is a unit of speed equal to one nautical mile per hour. Its kn abbreviation is preferred by American and Canadian maritime authorities, and by the Institute of Electrical and Electronics Engineers; however, the kt and kts abbreviations also are used.... )	Minimum Pressure (millibars)
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	Topics Dvorak technique Topic Home The Dvorak technique (developed in 1974 by Vernon Dvorak Vernon Dvorak Vernon F. Dvorak is a retired United States meteorology. In 1974, he developed the Dvorak technique to analyze tropical cyclones from satellite imagery.... ) is a widely used system to subjectively estimate tropical cyclone Tropical cyclone A tropical cyclone is a storm characterized by a large low pressure system center and numerous thunderstorms that produce strong winds and flooding rain.... intensity based solely on visible and infrared satellite images Weather satellite A 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 moving at the speed of the Earth's rotation.... . Several agencies issue Dvorak intensity numbers for cyclones of sufficient intensity. These include the National Hurricane Center National Hurricane Center The 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 tropical cyclone.... 's Tropical Analysis and Forecast Branch (TAFB), the NOAA National Oceanic and Atmospheric Administration The 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 Earth's atmosphere.... /NESDIS National Oceanic and Atmospheric Administration The 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 Earth's atmosphere.... Satellite Analysis Branch Satellite Analysis Branch The Satellite Analysis Branch, part of National Oceanic and Atmospheric Administration#National Environmental Satellite, Data, and Information Service ' Satellite Services Division, is the operational focal point for real-time imagery products within NESDIS.... (SAB), and 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 Naval Maritime Forecast Center in Pearl Harbor, Hawaii.... at the Naval Pacific Meteorology and Oceanography Center in Pearl Harbor Pearl Harbor Pearl Harbor is a harbor on the island of Oahu, Hawaii, west of Honolulu, Hawaii. Much of the harbor and surrounding lands is a United States Navy deep-water naval base.... , Hawaii Hawaii File:Pahoehoe and Aa flows at Hawaii.jpgThe State of Hawaii is a U.S. state in the United States, located on an archipelago in the central Pacific Ocean southwest of the continental United States, southeast of Japan, and northeast of Australia.... . le class="wikitable" style="float:right; margin-left:1.5em; width:25em; text-align:center">
T-Number		Atlantic	NW Pacific
1.0 - 1.5	25	----	----
2.0	30	1009	1000
2.5	35	1005	997
3.0	45	1000	991
3.5	55	994	984
4.0	65	987	976
4.5	77	979	966
5.0	90	970	954
5.5	102	960	941
6.0	115	948	927
6.5	127	935	914
7.0	140	921	898
7.5	155	906	879
8.0	170	890	858
Note: The pressures shown for the NW Pacific are lower as the pressure of that whole environment is lower as well.

In a developing cyclone, the technique takes advantage of the fact that cyclones of similar intensity

Tropical cyclone scales

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Encyclopedia

The Dvorak technique (developed in 1974 by Vernon Dvorak

Vernon Dvorak

Vernon F. Dvorak is a retired United States meteorology. In 1974, he developed the Dvorak technique to analyze tropical cyclones from satellite imagery....
) is a widely used system to subjectively estimate tropical cyclone

Tropical cyclone

A tropical cyclone is a storm characterized by a large low pressure system center and numerous thunderstorms that produce strong winds and flooding rain....
intensity based solely on visible and infrared satellite images

Weather satellite

A 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 moving at the speed of the Earth's rotation....
. Several agencies issue Dvorak intensity numbers for cyclones of sufficient intensity. These include the National Hurricane Center

National Hurricane Center

The 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 tropical cyclone....
's Tropical Analysis and Forecast Branch (TAFB), the NOAA

National Oceanic and Atmospheric Administration

The 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 Earth's atmosphere....
/NESDIS

National Oceanic and Atmospheric Administration

Satellite Analysis Branch

The Satellite Analysis Branch, part of National Oceanic and Atmospheric Administration#National Environmental Satellite, Data, and Information Service ' Satellite Services Division, is the operational focal point for real-time imagery products within NESDIS....
(SAB), and 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 Naval Maritime Forecast Center in Pearl Harbor, Hawaii....
at the Naval Pacific Meteorology and Oceanography Center in Pearl Harbor

Pearl Harbor

Pearl Harbor is a harbor on the island of Oahu, Hawaii, west of Honolulu, Hawaii. Much of the harbor and surrounding lands is a United States Navy deep-water naval base....
, Hawaii

Hawaii

File:Pahoehoe and Aa flows at Hawaii.jpgThe State of Hawaii is a U.S. state in the United States, located on an archipelago in the central Pacific Ocean southwest of the continental United States, southeast of Japan, and northeast of Australia....
.

Details of technique

**Dvorak T-Number and Corresponding Intensity**
T-Number	Winds (knots Knot (speed) The knot is a unit of speed equal to one nautical mile per hour. Its kn abbreviation is preferred by American and Canadian maritime authorities, and by the Institute of Electrical and Electronics Engineers; however, the kt and kts abbreviations also are used.... )	Minimum Pressure (millibars)
T-Number		Atlantic	NW Pacific
1.0 - 1.5	25	----	----
2.0	30	1009	1000
2.5	35	1005	997
3.0	45	1000	991
3.5	55	994	984
4.0	65	987	976
4.5	77	979	966
5.0	90	970	954
5.5	102	960	941
6.0	115	948	927
6.5	127	935	914
7.0	140	921	898
7.5	155	906	879
8.0	170	890	858
Note: The pressures shown for the NW Pacific are lower as the pressure of that whole environment is lower as well.

In a developing cyclone, the technique takes advantage of the fact that cyclones of similar intensity

Tropical cyclone scales

Tropical Cyclone are officially ranked on one of several tropical cyclone scales according to their maximum sustained winds and in what tropical cyclone basins they are located....
tend to have certain characteristic features, and as they strengthen, they tend to change in appearance in a predictable manner. The structure and organization of the tropical cyclone are tracked over 24 hours to determine if the storm has weakened, maintained its intensity, or strengthened. Various central cloud and banding features are compared with templates that show typical storm patterns and their associated intensity. If infrared

Infrared

Infrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves ....
satellite imagery is available for a cyclone with a visible 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....
pattern, then the technique utilizes the difference between the temperature of the warm eye and the surrounding cold cloud tops to determine intensity (colder cloud tops generally indicate a more intense storm). In each case a "T-number" and a Current Intensity (CI) value are assigned to the storm. These measurements range between 1 (minimum intensity) and 8 (maximum intensity). The T-number and CI value are the same except for weakening storms, in which case the CI is higher. The table at right shows the approximate surface wind speed and sea level pressure

Atmospheric pressure

Atmospheric pressure is sometimes defined as the force per unit area exerted against a surface by the weight of air above that surface at any given point in the Earth's atmosphere....
that corresponds to a given T-number.

Pattern types

There are several visual "patterns" that a cyclone may take on which put upper and lower bounds on its intensity. The primary patterns used are:

curved band pattern (T1.0-T4.5)
shear pattern (T1.5-T3.5)
central dense overcast (CDO
Tropical cyclone

A tropical cyclone is a storm characterized by a large low pressure system center and numerous thunderstorms that produce strong winds and flooding rain....
) pattern (T2.5-T5.0)
banding eye pattern (T4.0-T4.5)
eye pattern (T4.5 - T8.0)

Once a pattern is identified, the storm features (such as length and curvature of banding features) are further analyzed to arrive at a particular T-number.

Usage

The National Hurricane Center

National Hurricane Center

The 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 tropical cyclone....
will often quote Dvorak T-numbers in their tropical cyclone products. The following example is from discussion number 3 of Tropical Depression 24 (eventually Hurricane Wilma

Hurricane Wilma

Hurricane Wilma was the most intense tropical cyclone ever recorded in the Atlantic basin. Wilma was the twenty-second tropical cyclone , thirteenth tropical cyclone, sixth major hurricane, and fourth Saffir-Simpson Scale hurricane of the record-breaking 2005 Atlantic hurricane season ...
) of the 2005 Atlantic hurricane season

2005 Atlantic hurricane season

The 2005 Atlantic hurricane season was the most active List of Atlantic hurricane seasons in recorded history, repeatedly shattering previous records....
:

BOTH TAFB AND SAB CAME IN WITH A DVORAK SATELLITE INTENSITY ESTIMATE OF T2.5/35 KT. HOWEVER ...OFTENTIMES THE SURFACE WIND FIELD OF LARGE DEVELOPING LOW PRESSURE SYSTEMS LIKE THIS ONE WILL LAG ABOUT 12 HOURS BEHIND THE SATELLITE SIGNATURE. THEREFORE... THE INITIAL INTENSITY HAS ONLY BEEN INCREASED TO 30 KT.

Note that in this case the Dvorak T-number (in this case T2.5) was simply used as a guide but other factors determined what the NHC decided to set the discussion intensity at.

The Cooperative Institute for Meteorological Satellite Studies (CIMSS) at the University of Wisconsin-Madison has developed the Objective Dvorak Technique (ODT). This is a modified version of the Dvorak technique which uses computer algorithms rather than subjective human interpretation to arrive at a CI number. This is generally not implemented for tropical depressions or weak tropical storms.

**Satellite Images of Selected Tropical Storms and Associated T-Number**

Tropical Storm Wilma Hurricane Wilma Hurricane Wilma was the most intense tropical cyclone ever recorded in the Atlantic basin. Wilma was the twenty-second tropical cyclone , thirteenth tropical cyclone, sixth major hurricane, and fourth Saffir-Simpson Scale hurricane of the record-breaking 2005 Atlantic hurricane season ... at T3.0	Tropical Storm Dennis Hurricane Dennis Hurricane Dennis was an early-forming major hurricane in the Caribbean and Gulf of Mexico during the very active 2005 Atlantic hurricane season.... at T4.0	Hurricane Jeanne Hurricane Jeanne Hurricane Jeanne was the tenth named tropical cyclone, the seventh tropical cyclone, and the fifth major hurricane of the 2004 Atlantic hurricane season.... at T5.0	Hurricane Emily Hurricane Emily (2005) Hurricane Emily was the fifth named tropical cyclone, third hurricane, second major hurricane, and first Saffir-Simpson Hurricane Scale of the record-breaking 2005 Atlantic hurricane season.... at T6.0

External links

Agencies issuing Dvorak intensity estimates

(Advanced Dvorak Technique)

Other

Dvorak, 1974. (PDF, 1.3 MB)
Franklin and Brown
[https://confex.webex.com/confex/playback.php?FileName=http%3A%2F%2Fams.confex.com%2Fdata%2Fams%2Fwebex%2F26HURR%2F75544.wrf The Dvorak Technique Through Time] Dr. Jack Beven. (WRF File. Requires WebEx player)

Dvorak technique

Details of technique

Pattern types

Usage

See also

External links