Maximum sustained wind
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| Saffir-Simpson Hurricane Scale | ||||
|---|---|---|---|---|
| Category | Wind speed | Storm surge | ||
| mph (km/h) |
ft (m) |
|||
| 5 | ≥156 (≥250) |
>18 (>5.5) | ||
| 4 | 131–155 (210–249) |
13–18 (4.0–5.5) |
||
| 3 | 111–130 (178–209) |
9–12 (2.7–3.7) |
||
| 2 | 96–110 (154–177) |
6–8 (1.8–2.4) |
||
| 1 | 74–95 (119–153) |
4–5 (1.2–1.5) |
||
| Additional classifications | ||||
| Tropical storm |
39–73 (63–117) |
0–3 (0–0.9) |
||
| Tropical depression |
0–38 (0–62) |
0 (0) |
||
The maximum sustained winds of a tropical cyclone are a common indicator of the intensity of the storm. Unlike gusts, the value of these winds are determined via their sampling and averaging the sampled results over a period of time. Maximum sustained winds represent the highest winds expected over a one to ten minute time span anywhere within the tropical cyclone, depending upon the basin. In most tropical cyclone basins, they are determined with the use of satellite imagery. Land, ship, reconnaissance observations, and radar imagery are also helpful for determining this quantity, when available. This value can be helpful in determining damage expected from a tropical cyclone, through use of such scales as the Saffir-Simpson scale.
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[edit] Definition
Most weather agencies use the definition for sustained winds recommended by the World Meteorological Organization (WMO), which specifies measuring winds at a height of 10 m (33 ft) for 10 minutes, and then taking the average. However, the U.S. National Weather Service defines sustained winds by average winds over a period of one minute, measured at the same 10 m (33 ft) height.[1][2] Central pressure values are approximate. Intensity of example hurricanes is from both the time of landfall and the maximum intensity.[3]
[edit] Determination of value
In most tropical cyclone basins, use of the satellite-based Dvorak technique is the primary method used to determine a tropical cyclone's maximum sustained winds. The extent of banding and difference in temperature between the eye and eyewall is used within the technique to assign a maximum sustained wind and pressure.[4] Ship and land observations are also used, when available. In the Atlantic as well as the Central and Eastern Pacific basins, reconnaissance aircraft are still utilized to fly through tropical cyclones to determine flight level winds, which can then be adjusted to provide a fairly reliable estimate of maximum sustained winds. Depending upon the atmospheric conditions the tropical cyclone is embedded within, a reduction of 10 to 20 percent of the winds sampled at flight level is used to estimate the maximum sustained winds near the surface, though these values have been known to widely vary. Doppler weather radar can be used in the same manner to determine surface winds with tropical cyclones near land.[5]
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| Tropical Storm Wilma at T3.0 | Tropical Storm Dennis at T4.0 | Hurricane Jeanne at T5.0 | Hurricane Emily at T6.0 |
[edit] Relationship to tropical cyclone strength scales
In most basins, maximum sustained winds are used to define their category. In the Atlantic and northeast Pacific oceans, the Saffir-Simpson scale is used. This scale can be used to determine possible storm surge and damage impact on land. In all basins, the category of the tropical cyclone ( for example, tropical depression, tropical storm, hurricane/typhoon, super typhoon, depression, deep depression, intense tropical cyclone) is determined from the cyclone's maximum sustained wind. Only in Australia is this quantity not used to define the tropical cyclone's category; in their basin, wind gusts are used.[6]
[edit] References
- ^ Tropical Cyclone Weather Services Program (June 1, 2006). Tropical cyclone definitions (PDF). National Weather Service. Retrieved on 2006-11-30.
- ^ Federal Emergency Management Agency (2004). Hurricane Glossary of Terms. Retrieved on 2006-03-24. Accessed through the Wayback Machine.
- ^ National Hurricane Center (June 22, 2006). Saffir-Simpson Hurricane Scale Information. National Oceanic and Atmospheric Administration. Retrieved on 2007-02-25.
- ^ Atlantic Oceanographic and Meteorological Laboratory. Subject: H1) What is the Dvorak technique and how is it used? Retrieved on 2006-12-08.
- ^ J. TUTTLE and R. GALL. A single-radar technique for estimating the winds in tropical cyclones. Retrieved on 2008-06-12.
- ^ Bureau of Meteorology. Bureau of Meteorology: Tropical Cyclone Information Resources. Retrieved on 2008-01-17.]
