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Fig2.2-14(e):The forecast mean wave directions derived from the wind-sea and mean swell (as shown in Fig2.2-14(a)) superimposed on the previous chart (Fig2.2-14(d)).  This illustrates the important additional information that is gained from consideration of the wind-sea and mean swell forecasts together.  The mean wave directions (Fig2.2-14(a)) give no indication of that a sea passage to the west of Portugal is likely to be through confused rough seas.

Waves and swell with along a long period

Large swell waves with a long period breaking on a beach slope tend to have a large swash with water washed well up the beach.  This is often unexpected and takes people by surprise and can cause damage and casualties.  Users should note when large waves with a long period are forecast to run onto an exposed coast.  Extreme forecast index products for waves can alert users to the potential problem. 

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