Extreme High Swell Events on the Moroccan Atlantic Coast

4.0 Case Study 1 » 4.4 Step 3: Forecasting the Marine Situation » 4.4.7 WW111 Outputs in Selected Points

The tables show the WAVEWATCH III predictions of significant wave height, peak period, and direction of propagation for four points on the Moroccan Atlantic coast: Larache, Casablanca, Safi, and Agadir. The predictions are for 6-hour steps from 6 January at 0000 UTC to 8 January at 1200 UTC (60 hours).

WW3 wave model predictions of significant wave height, peak period, and direction of propagation for Larache, Casablanca, Safi, and Agadir; predictions for 6-hour steps from 6 Jan to 8 Jan 0000 UTC

For the night of 6 January and morning of 7 January, the WW111 model predicts significant wave height values of 6 to 7 m. These values are high. But what’s remarkable are the period values, which are approaching 18 s. The height of long-period swell increases significantly as they shoal and break in shallow water. Depending on the beach steepness, 7 m waves with an 18 s period can easily be 10 m high when they break.

These waves are extremely powerful. Remember the power of a wave is proportional to its period times the significant wave height squared (P=0,4 * Hs² * T (kW per m)).

Here’s the same output in graph form. You can see the predicted evolution of the waves’ characteristics at the four locations.

WW3 wave model predictions of significant wave height, peak period, and direction of propagation in graph form for Larache, Casablanca, Safi, and Agadir; predictions for 6-hour steps from 6 Jan to 8 Jan 0000 UTC