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Subject: D4) What does "maximum sustained wind" mean ? How does it relate to gusts in tropical cyclones ?

The National Hurricane Center (and the U.S. National Weather Service as a whole) uses a 1 min averaging time for reporting the sustained (i.e. relatively long-lasting) winds. The maximum sustained wind mentioned in the advisories that NHC issues for tropical storms and hurricanes are the highest 1 min surface winds occuring within the circulation of the system. These "surface" winds are those observed (or, more often, estimated) to occur at the standard meteorological height of 10 m (33 ft) in an unobstructed exposure (i.e., not blocked by buildings or trees).

Gusts are a few seconds (3-5 s) wind peak. Typically, in a hurricane environment the value for a peak gust is about 20-25% higher than a 1 min sustained wind. After a tropical cyclone makes landfall, the sustained winds tend to weaken rather quickly because of increase roughness over land. However, the gusts can be an even higher percentage of these weakened sustained winds due to increased turbulence.

One complication with the use of the 1 min averaging time for the standard for sustained wind in the Atlantic and Northeast Pacific tropical cyclone basins (where the United States has the official World Meteorological Organization tropical cyclone advisory responsibilities) is that in most of the rest of the world, a 10 min averaging time is utilized for "sustained wind". While one can utilize a simple ratio to convert from peak 10 min wind to peak 1 min wind (roughly 12% higher for the latter), such systematic differences to make interbasin comparison of tropical cyclones around the world problematic.

Last updated August 13, 2004

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