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Subject: D4) What does "maximum sustained wind" mean ?
How does it relate to gusts in tropical cyclones ?
Contributed by Chris Landsea
The OAR 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 occurring 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).
Since the inauguration of the Automatic Surface Observation
System (ASOS) the National Weather Service has adopted
a two minute average standard for its sustained wind definition.
This is because the ASOS stations average and report
their wind data over a two minute period. There is no conversion
factor to change a two minute average wind into a one minute average
wind, and it is pointless to try to estimate the highest one
minute wind over a two minute period, as they are essentially
the same.
Gusts are a few seconds (3-5 s) wind peak. Typically in a
hurricane environment, the value of the maximum 3 second gust over
a 1 minute period is on the order of 1.3 times (or 30% higher than)
than the 1 min sustained wind.
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.
Powell, M.D., S.H. Houston, and T.A. Reinhold, 1996:"Hurricane
Andrew's Landfall in South Florida, Part I: Standardizing measurements
for documentation of surface wind fields." Wea. Forecast.
v.11, p.329-349
Last updated April 21, 2006
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