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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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