Cornwall Swell forecast.

[Graham Easterling]

Monday 5pm

12 hours later the Hurricane Erin swell has arrived

Not only is a 5m swell decidedly big at any time of year, it's also very long period. 18-19 seconds for the dominant wave, as it's come well over 1,000 miles, so it is very powerful and guaranteed to give powerful rip currents. Bank holiday week visitors and still warm on Tuesday, a bit of a lifeguards nightmare along the north Cornish coast, as well as places like Porthleven & Praa Sands on the Lizard.

Graham

Penzance

[Graham Easterling]

The really significant feature of the coming swell is that it's developing for some period over quite a long fetch some way to the west. By the time it reaches Cornwall it's very long period and very powerful.

Note the wave energy forecast for Sennen. Tuesday would be impressive in mid winter.

Note the 1.1m swell with a 9 sec period is only half as powerful as a mere 0.5m swell with a 24 sec period. There is a rather complicated formula around all this, but the period is related to the speed of the wave.  Also there is a much greater volume of water associated with a long period wave. The very first storm waves to arrive might be small and look innocuous, but they are the longest period & powerful, more than capable of ripping boats from their moorings. They are also associated with big wave setup surges, bit like mini tsunamis. All a lifeguards nightmare on Tuesday really, as it'll still be warm & not that windy here. It can be dangerous even paddling when a surge comes in and instead of paddling on the edge you are waist deep in surging water. Not good for the Cornish holiday trade if young children get swept away. https://www.facebook.com/sennencovelifeboat/?locale=en_GB

Pleased to note the weather forecasts have picked up on it. West & north Cornwall, the outer Hebrides and west / south coast of Ireland main places affected. Less pleased to note half a forecast lately was taken up in promoting an online weather game.

Graham

Penzance

[Graham Easterling]

The first powerful waves have arrived on cue, they'll soon be a lot bigger.

Already getting an audience at Sennen harbour. A few swimming in the relative safety of the harbour. The fishing fleet pulled well up the slip.

Graham

Penzance

[Graham Easterling]

THe swell height forecasts, which showed a peak around 5.5m just off Lands End several days in advance, were pretty much spot on. Quite impressive really.

Total lack of any relationship between local wind strength & swell size (as opposed to sea roughness) , which is fairly typical on the Atlantic seaboard.

Graham

Penzance