GUIDE WAVE ANALYSIS AND FORECASTING - WMO

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In addition to the spectral information, the
WAVEOB code includes reports of derived wave parameters
like significant wave height, spectral peak period,
etc. The details of various sections of the WAVEOB code
can be found in Annex II and in the WMO Manual on
codes (WMO-No. 306, code form FM 65-IX; WMO,
1995). A binary format for reporting these data is also
available, namely BUFR (code form FM 94-X Ext.).
This code has been used experimentally for several years
to transmit ERS-1 satellite data over the Global Telecommunication
System.
For reporting wave model forecast products in
a gridded format, the approved code is called GRID
(FM 47-IX Ext.) (see WMO-No. 306) in which the location
of a grid point is reported first, followed by other
information as defined above. A binary version, called
GRIB, is now widely used.
6.4 Verification of wave models
With ocean wave models being used in operational
mode, appropriate verification of a wave model against
observed wind and wave data is necessary and import-
GUIDE TO WAVE ANALYSIS AND FORECASTING
Figure 6.3 — A sample output (12-h forecast, valid 12 UTC, 13 September 1992) from the regional Gulf of Mexico shallowwater
wave model operated by NOAA. The chart shows wave height values (in feet) and primary wave directions
plotted at alternate grid points of the model (source: D. B. Rao, Marine Products Branch, NOAA)
ant. The performance of a wave model must be continually
assessed to determine its strengths and weaknesses
so that it can be improved through adjustment or modifications.
It is also necessary to develop sufficient
confidence in the model products for operational use.
There are a number of levels of model testing and
verification. In wave model development a number of
idealized test cases are usually modelled. The basic
output of spectral wave models is the two-dimensional
wave spectrum and a suitable test would be to use the
model to simulate the evolution of a wave spectrum with
fetch or duration for stationary uniform wind fields. Data
from field experiments, such as the JONSWAP experiment
(see Section 1.3.9), can be used to assess the
model’s performance.
Ideally, a model would be verified by comparisons
with measured directional wave spectra. However, such
measurements are relatively uncommon and there are
problems with interpreting the results of comparisons of
individual directional wave spectra. For example, in
rapidly changing conditions, such as in storms, small
errors in the prediction of the time of the storm peak can