On Saturday, 9 August 2014 13:34:10 UTC+1, Graham Easterling wrote:


Taking the tip of Cornwall as an example, the peak swell forecast for Sennen is just 10', which typically occurs several times in a normal September, twice that height occurs several times a year, and last winter exceed 30' on several occasions.

Correction, latest forecast just 8', which is of no significance whatsoever and is exceeded on the large majority of months. It's forecast to be 10-12' on Tuesday, due to the persistent run of strong westerlies.

Do you mean 8 metres?
8 metres = 26 feet.

Off Land's a swell height of around 45' (well 13m - you convert it) has a 5 year return period. (Thanks Norman!)

Where is the data on these swells?
The best I can get are extreme tidal heights:
http://www.ntslf.org/tides/hilo?port=Newlyn

5 year returns have a correlation with the cycle of the seasons but that is not an exact time-scale. Even the 18.6 lunar nodal return doesn't correspond to such a thing exactly.