Extreme High Swell Events on the Moroccan Atlantic Coast

4.0 Case Study 1 » 4.5 Case Summary

Now, we’ll review what actually happened during the event and some of its impacts.

  • There was explosive cyclogenesis in the North Atlantic, characterized by deepening pressure of 36 hPa in 24 hours
  • There was a strong westerly wind to the south and southwest of the depression
  • The wind velocity reached approximately 40 to 50kt; recall that the wind speed is the first factor to consider in a wave’s growth and propagation
  • There was a long northwest fetch of about 3000 km, which was favorable for the wave’s propagation to the Moroccan Atlantic coasts
  • Ships in the high seas reported high swells of 7 to 8 m, with high periods of 20 s
  • Off the Moroccan coast, ships reported a significant swell height of 4.5 to 5 m, with a period of up to 18 s
  • The WW111 and WAM wave models gave good forecasts for both the significant wave height and period
  • The ECMWF Extreme Forecast Index shows a significant magnitude of about 0.8 to 1 on the north and central Atlantic Moroccan coast

Considering these characteristics, it’s clear that the swell that hit coastal Morocco was exceptionally powerful.

Here are some of the impacts of the event in the coastal areas:

  • In some places, the exceptional swells exceeded the projected swell heights for which the port infrastructures had been sized. This caused major disruptions of port traffic, and closed all of the ports on the Atlantic coast
  • The most significant incidents were reported at the following ports.
    • Mohammedia recorded very strong swells, with peaks exceeding 13 m
    • In the Safi harbor basin, 40 fishing boats and 35 other units were grounded
    • In Casablanca, four people were injured, and many terraced homes along the coast were damaged

Note that the arrival of strong waves coincided with high tides, making them an aggravating factor. The tidal range was about 3.5 m.