Experimental 5-Day Wave & Wind Forecasts : SIO and Torrey Pines
These experimental wave forecasts are being made in support of
Southern California Beach Processes Study
field operations and the
Nearshore Canyon EXperiment (NCEX).
The forecasts are made with a local, shallow water,
spectral refraction model
initialized with deep water forecast spectra from the global
NOAA Wavewatch III Wave Model at a location
offshore of San Diego (32N 118W). The model forecasts update every
12 hours. The real-time measurements on the plots are updated hourly.
The forecasts include both long period swells and short period,
locally generated seas. The Wavewatch III model does not resolve
the sheltering effects of islands offshore of Southern California
and the unaltered deep water forecasts tend towards overprediction.
To crudely compensate for the island blocking of sea and swell,
regional spectral refraction calculations at the 32N 118W Wavewatch III
forecast point are used to remove energy from the forecast
spectra from directions blocked by islands. The modified forecast
spectra are then used to initialize the Scripps local refraction
model to forecast wave conditions at CDIP buoy measurement sites
and at the end of the Scripps Pier.
Wind forecasts from two data sources are also shown when available.
1) The offshore AVN wind forecast from NCEP at the 32N 118W Wavewatch III
forecast point (green line), and 2) The
US Navy COAMPS wind forecast
for the measurement sites (red line, interpolated from a ~10km COAMPS
Our experience to date is that the wave model scheme underpredicts the
heights of the larger local sea events, which appear as a rapid
increase in the wave height concurrent with short peak wave
periods (4-8 seconds), and high local winds. This is most likely
owing to excessive directional blocking of the Wavewatch-III energy
in our modified deep water spectra. In addition, the
timing of the initial arrival of southern hemisphere swells
are usually off during
the summer, appearing as a gradual increase in energy over the
course of 24-36 hours, when the measured arrival energy appears
later and builds more rapidly. However, the forecasted time of
the peak in the height of the swell event is usually pretty close.