Sea surface temperatures across the North Sea are generally around 4 to 6°C at the moment (fig 2), which makes them slightly above average for the time of year by a degree or so, except that is for a band of colder water that extends from Denmark across to the Humber, where anomalies are 1 to 4°C below the normal (fig 1), which was no doubt caused by the prolonged periods of easterlies during the last couple of months across the Baltic.
Generally above average sea surface temperatures around the British Isles at the moment (fig 1). As high as 3°C above average at 65° north which is fast becoming the norm for this part of the Arctic ocean. There’s a warm pool in the central North Sea, and a tongue of warmer water along the eastern English Channel through the straits of Dover and on into the southern North Sea.
An interesting up welling of cold water off the Mauritanian coast of northeast Africa with SST anomalies of at least -3°C. I can’t see how the recent very cold air over this part of the world has affected the SST anomalies, but something obviously has.
What can you say about an SST chart like this? A ribbon of extremely warm anomalies affecting the eastern seaboard from Texas in the west to Nova Scotia, and then on, streaming out into the northeast Atlantic east of Newfoundland (fig 3).
The cold pool in the central Atlantic (fig 4) is still hanging on, and the cold weather in Iceland seems to have cooled the inland waters in the west.
Here are maps of SST anomalies just east of Newfoundland for the last three Decembers 2015 to 2017 (figs 1-3).
I know that it has some kind of bearing on the type of weather we get on our side of the Atlantic due to its influence on the jet stream and type of circulation patterns that we’re likely to see for the remainder of the winter. As far as I know negative SST anomalies in this region would favour blocking and more anticyclonic easterly weather, whilst positive anomalies, like they are at the moment, would mean increased mobility and storminess. So on the strength of the latest anomalies as high as +5°C (fig 3), our run of seven years without any snow lying in this part of Devon looks quite likely to be extended to eight.
I don’t have any papers I can include or quote from which explain this relationship in more detail, but I do have this recent comment in a newsgroup by Graham Davis who is more knowledgeable than most on the subject (I hope he doesn’t mind me quoting him).
“The reason for the recent lack of easterlies is the sea temperature anomalies in the North Atlantic haven’t been conducive. The important area in this regard is that immediately to the south of the Grand Banks. If this is colder than normal, the atmospheric pressure over Iceland tends to be higher than normal and lower than usual around the Azores. Conversely, a warm anomaly leads to below normal pressure in the southern Norwegian Sea and above average pressure in mid-Atlantic. These pressure patterns vary depending on time of year – due to changes in average jet-stream wavelength – and on the shape and position of the anomalies.
The last winter I can find with a cold pool in more or less the correct area during winter, although it was rather weak, was 2012-13 when Jan-Mar were anomalously easterly.
The predominance of the cold blob south of Greenland in recent years was suggested to be associated with a change in N Atlantic ocean currents. I pooh-poohed this idea at first but I’ve been coming round to it in the past couple of years. I’ve wondered whether this might be a sign that some of the Labrador Current is remaining on the surface and drifting eastwards instead of sinking below the Gulf Stream. This could be caused by a reduction in salinity of the current due to increased meltwater from the Greenland icecap entering the flow. If this is the case, it could be a sign that due to the bi-stable nature of the currents in the area we might be due for one of its flips and consequent sudden climate changes. The features of this change would be an intensification of the cold blob and a persistence of the warm anomaly south of 40N. This would mean we’d be stuck in almost permanent westerlies.“
I also noticed the importance of SST east of Newfoundland in this research paper “Observational evidence of European summer weather patterns predictable from spring” published by the National Academy of Sciences.
A slight shift to the east overnight of the showers running down the Irish sea, also noticeable to the east are the band bands of very heavy wintry shower that are running down the east coast (fig 1). If you remember yesterday there were dual bands of showers running south down the Irish Sea, starting just west of the Isle of Man to western Cornwall, here are the estimated precipitation totals from 06 UTC on Thursday showing their track and extent (fig 2). You can still make out the dual bands that seem to split over Pembrokeshire.
This is no kind of scientific report about what goes into the formation and continuation of these bands, but someone did kindly point me to an article from the Quarterly Journal of the Royal Meteorological Society that does go into it some detail about them. Just for completeness, here are the latest SST anomalies from around the British Isles (fig 3), and you’ll notice that the SST down much of the central Irish Sea is running 1°C above the long-term average at the moment.
You can tell just by looking at these sea surface temperature charts since 2015 (figs 1-3) that there’s been considerable warming going on in the last two years. The cold anomaly that was a feature for so long in the central Atlantic is now less intense and much smaller a feature than it once was. It’s shifted and has been squeezed further northeast towards the southeast coast of Greenland and the opening of the Labrador Sea. The other notable difference that’s appeared in recent months is the area of warmer SST anomalies ~1500 km to the west of Portugal (42N 17W), a warm blob if you like.
The warm blob and this coming winter
To be honest I don’t have a clue if this warm blob will have the slightest effect on the weather in the British Isles this coming Winter. It would be nice to think that the area of warmer SST might weaken the Azores high in some way, and that might increase cyclonic development in the southeast Atlantic which will run northeastward towards Biscay – who knows. Looking at the actual MSLP anomalies (fig 3) for so far this month, it’s true that the Azores high is displaced further to the northeast, but all this has done has been to increase the strength of the zonal flow across the Atlantic. In fact everything seems to be enhanced in some way, if you look at the underlying anomalies (red dashed line) both highs and lows have been more intense in the first three weeks of November 2017 than usual.
My first reaction to this article in the Weatherwatch section of the Guardian was to measure the distance in miles between the Isles of Scilly and the nearest 26°C SST isotherm and then divide by thirty!
And so if the North Atlantic did continue to warm at this rate (with the 26°C SST moving 30 miles every 10 years), you can expect the 26°C SST isotherm to be lapping on the beaches of the Cornish Riviera in a little over 692.7 years in the late summer of 2709!
I do think Paul Brown did manage to completely miss the point with this article about Ophelia though, and instead of repeating the “hurricanes only form over water of 26°C” mantra like we’ve never stopped hearing from the BBC weather presenters of late, the question that he should have been asking was “why did Ophelia intensify to a major category three hurricane over an Ocean with marginal SST of between just 22 and 24°C“?
Ophelia was born on the 9th of October as a tropical depression at 09 UTC in the mid-Atlantic somewhere to the southeast of the Azores. Her early days were spent meandering around the place of her birth, at times it almost appeared that she was going around in circles. Then suddenly one day her life found a new direction, and she decided to head off and take a swipe at the British Isles, so off she went tracking ever more faster each day in a northeasterly direction. She made good progress, and before long she surprised every on by becoming a category 3 major hurricane! She had become the furthest east major hurricane in the satellite era! But then rather unexpectedly (to some people’s mind’s at least) and just as she was closing in on her intended target, someone called (Ice) Berg in America decided that her life as a hurricane was at an end, and he declared her a post-tropical cyclone! Not to be outdone she put on an extra spurt and deepened from 971 to 958 hPa to show them she was not finished quite yet. The rest as they say is history…
For the purists out there that say that hurricanes can only survive in oceans with a SST of around 79 °F (26 °C) or more, how did Ophelia manage to steadily intensify from a category 1 to a category 3 major hurricane in the Atlantic Ocean during on the 14th of October southeast of the Azores, with SST that were much colder (fig 2), between only 22°C and 24°C?
Please don’t bother replying with comments about how “the large temperature contrast between the abnormally warm seawater and the extremely cold temperatures in the upper atmosphere” providing instability for Ophelia’s thunderstorms “which allowed the storm to continue strengthening” because I simply won’t’ believe you!
If Ophelia can intensify over cooler waters like she did, then there is no reason not to accept that the NHC killed Ophelia off around 12 hours too soon, I think she survived till at least 09 UTC on the 16th of October and close to 51° north. She might have looked pretty crappy in the visible images as she approached Ireland early on Monday but her inner core winds that had driven her down to 951 hPa were still spinning.
FAAM and its relationship with the Met Office
Why wasn’t it possible for the Chief forecaster at the Met Office to call on the services of the Facility for Airborne Atmospheric Measurements [FAMM] and get them to fly their modified BAe 146-301 large Atmospheric Research Aircraft [ARA] to the Azores on Saturday afternoon and back again during Sunday, drop a couple of dropsondes into the eye of Ophelia, and run their fancy array of sensors over her?
All their findings could have been passed onto the NHC and fed directly into the NWP models around the world to get a better fix and track on Ophelia during the next 24 hours, all excellent meteorological research.
How come the Americans can afford to send a hurricane hunter out every six hours to investigate a tropical cyclone whenever an island in the Caribbean or the coastline of America is threatened, and yet when the tail end of a hurricane threatens our shores, we just curl up with a good book and issue a couple of warnings?
Of course it may have been that they did ask them, but maybe they were just too busy investigating stratocumulus, volcanic ash or contrails, and just couldn’t find the time for a jolly to the Azores.
When I was an assistant at Kinloss we had installed a boundary layer sonde [BLS] system from Vaisala, as did a number of other RAF stations across the UK. And when there was anything interesting going on meteorologically, we would fill up a balloon with helium, attach a small package of sensors to it, and throw it into the air. The rest was more or less automatic, a radio receiver attached to a PC processed the upper air data into a regular WMO TEMP message.
What I’m rather long-windedly trying to suggest, is that back then we realised the importance of good observational data, even when we had an excellent upper air network, something we don’t have these days. We don’t launch radiosondes from Weather Ships, we don’t even launch them from Stornoway, Shanwell or Hemsby these days, so why can’t we very occasionally just use something that we do have. I know the FAAM aircraft is primarily for research, but for exceptional hurricanes like Ophelia surely this could have been waived. As far as I know not a single aircraft from either Portugal, Spain, France, the UK or Ireland went out to take a look at Ophelia, surely the air force of one of these countries could have?
Just a ‘normal low pressure system’ says Chris Fawkes
I’m personally fed up to the back teeth of being told by weather presenter after weather presenter that Ophelia was now no longer a hurricane, and as Chris Fawkes so eloquently put it yesterday “is just a normal low pressure system”. Many of us don’t need this constantly rammed down our throats, or the 50 second video of Tomasz Schafernaker waving his arms about like some born again Magnus Pyke describing how a hurricane is formed and what powers them, because we already very well what the latest theories are.
I noticed this interesting article about polynya on the Phys.org website (you might what to add this to your favourites because it looks a great site) that might interest some of you out there. I was thinking, it’s only because the upwelling of warm water occurs under an ice sheet that we realise that they’re happening at all. They must happen all the time in the worlds oceans, but we just don’t see them, apart I suppose from anomaly charts of very sensitive SST satellite sensor data.
The Guardian must have known they were onto a winner with this article from the great Michael Mann about Hurricane Harvey, who states categorically in the article that Hurricane Harvey was made more deadly due to climate change (fig 1). I wonder just how many comments this article will attract?
Michael Mann states that one of the main factors why it was more deadly was due to higher than average SST in the Gulf of Mexico. So I thought that I’d have a quick look and see what the latest anomalies were across the North Atlantic, Caribbean and Gulf of Mexico to see if what he was saying was correct. Courtesy of NCOF, here are the SST (fig 2), on which I’ve drawn a very approximate track for the path of tropical cyclone Harvey, which as far as I can see from the NHC records, sprang into life as a cyclone at around 54° west on Thursday the 17th of August. Harvey has had a very fitful life, it ‘died’ as a tropical storm as it entered the Caribbean late on Saturday the 19th, before being reborn again as a tropical depression on Wednesday the 23rd as a tropical depression in the Bay of Campeche, the rest as they say is history.
All that you can say about the SST anomalies along the path of Harvey was that they were generally in the slightly warm category +0.5 to +1.0°C for much of its life. Interestingly these ‘higher’ than average SST in the Caribbean didn’t seem to stop it from dying for four days though, and it wasn’t till it entered the Bay of Campeche that it was reinvigorated. Because the SST anomalies in the above chart (fig 2) are in a bit of a turmoil after the passage of what was a category four hurricane, I have included an extra chart (fig 3) from the 23rd and before the waters got churned up. The SST anomalies in that chart show anomalies between +0.5°C and 1.5°C, generally across coastal regions of Texas extending eastward to Florida, with negative anomalies of the coast of the Yucatan peninsula.
So what caused Harvey to reform and quickly turn nasty as she entered the Gulf of Mexico? I personally don’t think it was ‘more deadly’ because the waters of the Gulf of Mexico were slightly warmer than average, I think it was more to do with the atmospheric mechanics that were driving Hurricane Harvey, of which the SST, although important are just one factor. Anyway now that I have provided one piece of the evidence you can make your own minds up.
Not surprisingly, the sea surface temperatures in the Mediterranean, are generally well above the average for this time in August, no doubt helped by the recent hot and sunny weather of the last week or so, with anomalies of +3°C above average in parts of the Adriatic, and off the Costa Calida in Spain. There’s also a curious tongue of colder water that seems to project westward into the northern Aegean sea. The SST in the coastal waters around the UK, are above average in the west and the southeast, but cooler than average in the southwest, and along the east coast from Fraserburgh down to the Humber.