EM 1110-2-1100 (Part II)
(Change 1) 31 July 2003
EXAMPLE PROBLEM II-2-6
FIND:
The expected maximum sustained wind speed for this storm for surge and/or wave prediction and
the maximum 1-min wind speed.
GIVEN:
A hurricane located at a latitude of 28o with a central pressure of 935 mb and a forward velocity of
10 m/s.
SOLUTION:
Using Figure II-2-17, the maximum wind speed in a moving storm with the parameters given here
is approximately 47.3 m/s for a 15- to 30-min average at the 10-m level. From Figure II-2-1, the ratio
of a 30-min wind (chosen here to give a conservative approximation) to a 1-min wind is approximately
1.23. Multiplying this factor times 47.3 yields a 1-min wind speed of 58.2 m/s (130 mph).
i.
Step-by-step procedure for simplified estimate of winds for wave prediction.
(1) Introduction. This section presents simplified, step-by-step methods for estimating winds to be
used in wave prediction. The methods include the key assumption that wind fields are well-organized and
can be adequately represented as an average wind speed and direction over the entire fetch. Most engineers
can conveniently use computer-based wind estimation tools such as ACES, and such tools should be used in
preference to the corresponding methods in this section. The simplified methods provide an approximation
to the processes described earlier in this chapter. The methods embody graphs presented earlier, some of
which were generated with ACES. The simplified methods are particularly useful when quick, low-cost
estimates are needed. They are reasonably accurate for simple situations where local effects are small.
(2) Wind measurements. Winds can be estimated using direct measurements or synoptic weather charts.
For preliminary design, extreme winds derived from regional records may also be useful (Part II-9-6). Actual
wind records from the site of interest are preferred so that local effects such as orographic influences and
sea breeze are included. If wind measurements at the site are not available and cannot be collected,
measurements at a nearby location or synoptic weather charts may be helpful. Wind speeds must be properly
adjusted to avoid introducing bias into wave predictions.
(3) Procedure for adjusting observed winds. When ACES is unavailable, the following procedure can
be used to adjust observed winds with some known level, location (over water or land), and averaging time.
A logic diagram (Figure II-2-20) outlines the steps in adjusting wind speeds for application in wave growth
models.
(a) Level. If the wind speed is observed at any level other than 10 m, it should be adjusted to 10 m
using Figure II-2-6 (see Example Problem II-2-3).
(b) Duration. If extreme winds are being considered, wind speed should be adjusted from the averaging
time of the observation (fastest mile, 5-min average, 10-min average, etc.) to an averaging time appropriate
for wave prediction using Figure II-2-1 (see Example Problem II-2-1). Typically several different averaging
times should be considered for wave prediction to ensure that the maximum wave growth scenario has been
identified. When the fetch is limited, Figure II-2-3 can be used to estimate the maximum averaging time to
II-2-34
Meteorology and Wave Climate
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