Extreme High Swell Events on the Moroccan Atlantic Coast

5.0 Case Study 2 » 5.5 EFI for 18 January

In analysing the Extreme Forecast Index values from 18 January at 0000 UTC to 19 January at 0000 UTC (a 24- to 48-h forecast), we find values of around 0.8 to 0.9 near the center of Moroccan Atlantic coast during the day of 18 January. This indicates the likelihood of an exceptional marine situation.

ECMWF Extreme Forecast Index valid for January 17, 2014 at 0000UTC forecast t+24 to 48

Question

Given the WAVEWATCH III's significant wave height of 6 to 9 m at the Moroccan central coast (particularly Casablanca) and the EFI values of about 0.8 to 0.9 for January 18, can we talk of an extreme wave height yet?

Even with a wave height approaching 7 m and EFI values of 0.8 to 0.9, it’s not yet clear if we’re facing an extreme event. Experience shows that some situations, even with wave heights of 7 m, have no coastal damage or other significant impacts. We need to analyze other information, such as period, before deciding on the magnitude of the situation.

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