As Jiries has been pointing out, SSTs off the East coast and, particularly, the channel off Hampshire and Dorset have remained stubbornly low throughout this hot spell. In fact they have cooled slightly in the last couple of days.

I am posting from an iPhone so can't get the link to the wetterzentrale map or the NOAA anomaly maps - maybe someone else can post the links. Anyway, there is a large patch of sub-15C SSTs in the channel, and another arm of cold water stretching down the Irish Sea. The strange thing is both are surrounded by much warmer (17C+) seas. The anomaly maps show how odd this is. There are yellows and oranges all around the British isles but for 2 patches of blue in the areas that have seen some of the hottest air temperatures. Odd.

Any ideas as to why? Could upwelling be responsible? Or runoff from cold groundwater fed rivers (I'd have thought that would be too small an input).

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That is something I've noticed as well. I'm sure that the long cold spring will have something to do with it but other than that I don't really have any hard facts to hand to back it up. It's just how it often felt quite cool and fresh along the coast even now - or maybe it's has always been like that as part of a maritime type climate what with me living in a coastal town and I've only just properly noticed it recently (over-analyzing it).
   I was going to say on how it has the effect of killing off french imported thunderstorms but the events of Tuesday morning suggests that doesn't seem to be the case.

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It suggests to me that sea-surface temps have little to do with air temps and what's going on in the atmosphere but plenty to do with underwater temps and circulations.

Critical atmospheric conditions are mostly visible (clouds) and measurable (air temps at various heights), so as surface dwellers we focus on these. But measurements of temperature, salinity and density at various levels and sites in the sea aren't perhaps as comprehensive. And while sea-surface currents may be measurable, knowledge of underwater circulations appears to me to be at best imprecise and at worst a mystery. I mean, I understand the principle of sampling compounds in the water and calculating when they were last exposed to air, but there's a hell of a lot of water out there to be sampled, even in the Channel.

And as a huge body of liquid (the sea) retains heat for longer than a huge body of gas (the atmosphere), we could be talking about changes which took place decades or even centuries ago which are only now reaching the surface of the sea.

So to answer the question in the opening post: I don't know.

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Good post. I've always thought that SST's, although influenced by weather above, are often more affected by currents beneath the surface that drag up different temperatures from time to time,in this case cold water 

Upwelling of colder waters does seem a good theory. Could mean bountiful times for sea life as sediments are brought up to the surface waters

http://ghrsst-pp.metoffice.com/pages/latest_analysis/sst_monitor/ostia/sst_anom_0_600.png

A large stretch of the western coasts has some impressive positive anomalies at the moment

Pan west and then south and you can see distinct bands of positive and negative anomalies across the Atlantic. Not long ago it was uninterrupted from out west of Spain to the Channel and southernmost North Sea, but since then the hot conditions in the Bay of Biscay have had a marked impact there, forming a notable break in the -ve anomalies.

A large part of the North Sea is now above average, very much so in places.

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The localised Meteociel SST map shows it up well - image is hosted on imgur so hope ok to display.

 

...and here's a stupid thought for the day ... does volume of shipping continually churn up the Spring cool waters from below, thus preventing the atmospheric warmth having the same effect as elsewhere?

My guess would be that only many, or some, days the sea was blanketed by mist and fog so has warmed slowly.

I'm guessing SST's locally are about 2C below normal. The sea clarity has been exceptional this year, I would estimate on calm days I can see around fifty feet down. This due to less plankton and algae in the water.

This time of year you would expect the sea to resemble a very thin soup, it hasn't happened this year.

I don't think SST's are understood very well at all.  Look at the tide height today in the SE corner of the Bay of St.Malo where the Channel Islands are located, you are looking at tide heights today of over 13.6 metres. That produces a lot of tidal stream in the local area, if I look out my window I can see the tide moving at over eight knots at times, that is a lot of turbulence and mixing.

I can imagine more turbid water would absorb heat more effectively. The warmest channel water I can remember swimming in was off Normandy in 1990 and the water was positively soupy. Maybe the cold winter killed off the algae.

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Yes, and there are areas measured in square miles where the tide comes in over warm rocks/sand heated by the summer sun, that certainly raises temps. temporarily much in what you are describing off the Normandy coast.

Shallow waters have certainly warmed up hugely! I was in Dorset at the weekend and the sea at Studland was as warm as I have ever felt it in the UK. The thermometer on my watch, which is normally pretty accurate (17-18C at the warmest when I usually go swimming in this country) registered 22C on Saturday and 23C on Sunday and Monday!

Granted the water at Studland is very shallow indeed, and this was in the afternoon when the sun had been heating it up all day but I was really staggered how warm it felt, when the SSTs have been so low up to now.

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I walked along the water edges at Worthing Beach last Sunday and it was warm after you felt cold at first.  It pebble beach but when the tide goes out it reveal very nice sandy beach.

I notice the warm sea temps over east Baltic moved westward.  2 years a pool of sub 5C remain all summer on east Baltic sea.  I also thinking if the temps of 15C being stuck are not accurate?