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200 PM EDT WED OCT 12 1994
TO: ALL NWS OFFICES
DOMESTIC DATA SERVICE
FROM: FRED ZBAR
ACTING CHIEF, SERVICES DEVELOPMENT BRANCH
SUBJECT: IMPLEMENTATION OF NEW OCEAN WAVE GUIDANCE
(THE FOLLOWING INFORMATION WAS PROVIDED BY H. S. CHEN OF THE
MARINE PREDICTION BRANCH OF THE NATIONAL METEOROLOGICAL CENTER)
On October 12, 1994 at 1200 UTC a new ocean wave model (NOAA/WAM)
will be implemented. The new ocean wave guidance will
incorporate the changes in bulletins and graphics that have been
implemented since TPB No. 388 came out. More importantly the
second generation wave model (NOW Model) which was used to
compute the wave spectra will be replaced by a third generation
model (NOAA/WAM) which explicitly computes nonlinear wave-wave
interactions and places no artificial limitations on wave growth
or decay.
The bulletins and graphics of the new guidance follow the same
formats shown in TPB No. 388, Except for the following
differences:
- (1) The new wave frequency (period) values and their
corresponding bandwidths are different from those in TPB No.
388. The number of new wave frequencies produced by the
model is 25 compared with 15 for the NOW model, but the new
frequencies have been combined to give only 15 values, so
the bulletin sizes will remain about the same.
(2) In the new guidance, the mean wave direction and mean
wave period are used, rather than the wave direction of the
dominant wave and the period of the peak frequency in the
wave spectrum. This is because these parameters are more
stable and are closer to what an observer reports than those
used previously.
- (3) There are fewer alphanumeric bulletins in the 1200 UTC
cycle than the 0000 UTC cycle because of limitations on AFOS
and agreements reached between the NWS Eastern and Western
Regional Headquarters and the NWS National Headquarters.
The ocean wave guidance will continue to be generated twice daily
based on the 0000 and 1200 UTC cycles of the Aviation model, but
using data supplied by the NOAA ocean wave model (NOAA/WAM).
Technical Procedures Bulletin No. 388 is now operationally
obsolete and will be superseded by a new Technical Procedures
Bulletin currently being reviewed.
If you need further information about the technical aspects of
the new ocean wave model, please call Dr. Hsuan Chen of the
Marine Prediction Branch of the National Meteorological Center at
(301)-763-8133.
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