Extreme High Swell Events on the Moroccan Atlantic Coast

4.0 Case Study 1 » 4.3 Step 2: Compare the Marine Model Analyses with the Observations » 4.3.6 Step 2 Summary

Here’s a summary of the weather situation during the two days before the event, using the observations and model analysis:

  • The MSG satellite imagery shows a large depression moving northeasterly over the North Atlantic Ocean. On the Moroccan coast, the situation is stable with few low clouds, coastal fog patches, and weak winds
  • The MSLP analysis shows low pressure with an explosive deepening (35 hPa per 24 hours) and a high pressure gradient. The northeasterly movement of the system has led to a large zone of strong northwest winds that blow for more than 24 hours and form a long fetch of about 3000 km.
  • The ASCAT observations show winds of about 40 to 50kts south of the low pressure.
  • Ship observations show high waves (8 m) with a long period (2 s) in the middle of the Atlantic Ocean, and waves of about 3 m increasing rapidly to 5 m offshore the Moroccan coasts.
  • The WW111 and WAM wave model analyses show high significant wave height near the low pressure center that are propagating towards Moroccan coasts.

All of this indicates that the situation will be unusual and that forecasters should be aware and take the appropriate action in accordance with the marine forecast process.

Question

Manual Wave Forecasting Diagram

Using this information and the nomogram, what significant wave height is expected?

A wind of about 40 to 50kt (20 to 25 m/s) blowing over 24 hours will create wave heights of 8 to 12 m.

Manual Wave Forecasting Diagram with feedback for an exercise overlaid on nomogram
Please make a selection.