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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 output grid).

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.
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