Penzance & West Cornwall Heavy Rain, Sun, BIG Swell

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Graham Easterling

May 18, 2022, 8:32:34 AM5/18/22
to Weather and Climate
Yesterday (17th) saw 10.4mm, all in just 3 hours, from 11:30-14:30. The wettest 09:00-09:00 period since 11.0mm on 7th April. 

This morning low cloud broke to give good sunny spells, though it's now (13:00) generally cloudy. Low cloud just capping the tops of the moors at times. Cloud base 500' to 750'.

With a deep low stuck in mid Atlantic, an unusually big & powerful swell for the time of year. Particularly big yesterday, big still a good 10' in the big sets this morning. I abandoned any idea of going bodyboarding. OK when I was 17, but not at 70.

Sennen 11:00 F4 offshore SSE wind, air across west Cornwall full of salt spray, seriously affecting visibility.


A very powerful long period swell.

To give an idea how important period is:-
A fairly locally generated 8 second period, in deep water
Wavelength 56m  Velocity 21mph
Currently, the dominant swell is 14 seconds, in deep water
Wavelength  a huge 305m, Velocity 49mph

Obviously, as the swell approaches the shore itn slows due to friction with the sea bed., the water piles up and surges forwards as the wave breaks. With a long period wave there is vastly more water to surge forward, and it is so much faster. When it comes to power, period is much more significant than height. In this case there was a fair bot of height as well.

I left it to the hardy. The lifeguards kept the beach open, luckily it's low tide midday.

Looks like the rain is pushing north across Devon at the moment


Graham Easterling

May 19, 2022, 4:02:46 AM5/19/22
to Weather and Climate
Thundery air well to the east now, the swell has gone down, the salt spray's largely gone, E visibility & deep blue skies.

2022-05-19 08_49_46-Capture.png

The big sea has stripped the sand from the top of the beach, it won't have gone far, near the low ride mark. 

Only a F1-2 SW wind here in Penzance. 2.1mm of rain in the 24 hours to 09:00 today. 30.1mm so far this month.


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