The 23.5°C at 12 UTC, makes the 21st the warmest day this month by a long way at Exeter Airport. Locally here 14 km to the northeast of the airport, the temperature has been well in excess of 25°C for the last couple of hours in the intense August sunshine, and it feels quite close.
The above reanalysis chart for the 00 UTC on the 12th of September 1961 (fig 1), shows four simultaneously active hurricanes in the North Atlantic and Gulf of Mexico. I’m not sure if that’s a unique occurrence, but I came across a mention of it in a book called The Atmospheric System which I’ve just picked up from Abe book. The contouring is not perfect because the reanalysis grid is too coarse at 2.5° x 2.5° to pick up the intensity of each hurricane.
Hurricane Debbie reached a maximum category 3 status, with a minimum pressure of 970 hPa and maximum wind speeds of 105 knots, in it’s life of almost 10 days it travelled 7,688 nautical miles (fig 2). This was very early days for weather satellite imagery, which explains the scarcity of tropical storms (2) listed for the 1961 season in the North Atlantic.
Hurricane Debbie was a classic Cape Verde hurricane that curved north and then northeast to brush across the northwest coast of Ireland as a category 1 hurricane causing the deaths of 17 people as it did so (fig 3). In fact it even hit the cape Verde Islands as a strong tropical storm, and was probably responsible for the death of 60 people in a plane crash on the island at that time. Wikipedia has a very detailed article about Hurricane Debbie, oddly they seem to like using the term ‘storm’ when referring to Debbie, despite referencing an article which is in no doubt that it was a category 1 hurricane at the time, as is the HURDAT2 database, which lists Debbie as a hurricane when it crossed Belmullet in Northwest Ireland, as you can see from the table of 6 hourly positions from it (fig 4).
That article mentioned in Wikipedia is from a book Advances in Hurricane Research – Modelling, Meteorology, Preparedness and Impacts by Kieran R. Hickey and Christina Connolly-Johnston, of the Department of Geography, at the National University of Ireland, Galway. Chapter 9 of the book is called The Impact of Hurricane Debbie (1961) and Hurricane Charley (1986) on Irelandis free to download as a PDF. Here are a couple of interesting effects of hurricane Debbie that I hope the authors don’t mind me taking these snippets from that chapter:
At Malin Head on the extreme NW tip of Ireland a gust of 182 kph (92 kts) was recorded. Other exceptional gusts were recorded at Shannon Airport, Rep. of Ireland at 172 kph (93 kts), Ballykelly, Northern Ireland at 171 kph, Tiree, Scotland and Snaefell, Isle of Man both at 167 kph (90 kts), Clones, Rep. of Ireland at 161 kph (87 kts), Kyle of Lochalsh, Scotland 159 kph (86 kts) and Mullingar, Rep. of Ireland with 146 kph (78 kts).
The severity of the wind can be seen by the fact that as far as 20 km inland all plant life withered and died in a matter of minutes as sea spray laden with salt was carried landward by the wind.
A very rare storm-induced tidal bore was recorded as having taken place on the Shannon river near Lanesboro, Co. Longford when the level of the river rose by 1.35 m as the hurricane winds blew water upstream. This reverse flow carried many small boats upstream and onto the river banks leaving them high and dry when the wind changed direction and the river dropped almost equally as suddenly.
Ever wondered what a scatter graph of hourly temperatures for a year looks like? The chart above (fig 1) does exactly that for Exeter airport, along with a 24 hour (black) and 7 day centred moving averages to boot. The cool morning temperature of 5.8°C from the airport, reminded me that Autumn is on its way, even though for the first few days of the coming week 1000-500 hPa partial thicknesses will be in excess of 564 dm. The 7 day moving average which peaked in June at close to 20°C, and has been declining erratically since the middle of July.
The sunshine stats may well be a little low for Exeter, with an annual total of just 1414.3 hours, this is because the sunshine record is not 100%. There are occasionally missing values from the SYNOP reports that I can do little about, December 2016 had quite a number, and might explain the odd behaviour of the moving average (fig 2). Even so, the sunny spells that did occur in early April, and in the second half of May are clearly visible, as is the warm and sunny June in both temperature and sunshine graphs.
I thought that I would look and see what were the wettest places in the UK by counting up the number of rain days there had been this summer since the 1st of June. Remember that rain days are days when 0.2 mm or more of rain has fallen in 24 hours, using SYNOP climate data that means in the 06-06 UTC period, either from the 24 hour total reported at 06 UTC, or from adding up the 12 hour totals for the period 06-18 and 18-06. I could have counted the number of wet days, which includes days with 1 mm of rain or more. As you can see from the above infographic (fig 1), Tulloch Bridge in Perthshire has the most number of rain days this summer, with 64 out of 79 days(81%). The lowest number are not surprisingly all across southern counties of England, with nine stations reporting less than 40% rain days so far this summer, headed by the St Catherine’s Point on the Isle of Wight, with only 24 rain days so far (fig 2).
And if we look a little further south across the Mediterranean this summer we’ll see what really dry looks like, with many places seeing only a single rain day so far.
The panel of eight charts are all from the GFS model runs of the last eight days (fig 1). They display the same forecast chart for midnight tonight (Saturday the 20th August 2017), but all from different model runs and forecast ranges, from the oldest of T+192 (last Friday midnight’s run), to the latest T+24 (this Friday midnight run). I’ve done this to see just how much the forecasts differs as we get closer to T+0, the forecast day we are interested in. The chart at the top right is from the furthest out (T+192) and the chart at the bottom right is closest to the forecast (T+24), I did this to compare just how the GFS was handling the approaching remnant s of ex-hurricane Gert on Saturday night.
As you can see, the forecast for Saturday night has changed quite radically in the last week. The rain from the approaching warm front was at first [T+168] expected quite quickly over Western Scotland and Northern Ireland, but from Thursdays run the model slowed it down and brought the area further south. The ridge of high pressure that was at 15° west at T+192 also changed position and alignment quite a lot in each run, and by the end is aligned NW-SE rather than N-S as it was at T+144.
What I’ve learned from this little comparison of the GFS, is that there is not a great deal of consistency before T+72, and it’s only from then that things start to firm up, but even when have, this by no means that the model has locked onto the correct solution.
Earlier this week I was spouting on about how ex-hurricane Gert would usher in a change of type and that by the end of next week summer would have made a home back. That was on Thursday, but the latest guidance from the NWP models suggest that once the low (that was the remains of ex-hurricane Gert) has finally struggled to cross the country, which looks like it will take most of the week, things will have changed very little, and mobility will be resumed after just a brief incursion of warm and humid air from the continent for a couple of days at the start of next week. Having said that, I did hear on the BBC weather that the models are having a torrid time on what effect Gert will have on the forecast for later this weekend, but looking at the latest run from the GFS and the UKMO models, their solutions for Monday do look remarkably similar (fig 1 & 2).
Today’s showers were a lot sharper than forecast by the Met Office model that was used in the BBC forecast on Spotlight yesterday evening (fig 1), with some white pixels in the weather radar, indicating intensities of >32 mm an hour (fig 2). Thankfully they were moving quickly.
Neither was there any mention in the forecast of any thunderstorms in any of today’s showers over the southwest of England (fig 3).
Just checking to see how they did on last nights national forecast, and again no mention of any thunderstorms (and any flashing lightning graphics), or of the intense showers indicated by the weather radar. All Darren Bett seem to be interested in was saying how cool it will be, he must have been out of the country for the last four weeks or so. All I can think is that the new Met Office model is having problem in convective situations like this, I am assuming of course that the BBC are still using Met Office NWP data at the moment!
Or did they mention this large area of very heavy rain in the afternoon over Wales in earlier forecasts. Is it only me that notices just how poor the weather forecast was?
Yesterday’s showers up through the spine of Cornwall and Devon were another classic example of showers caused by peninsular convergence. It also goes under the less prosaic name of the Brown Willy effect, it’s amazing what you can find courtesy of Wikipedia. The first thing you will notice that yesterdays string of showers seem to originate a little south of Brown Willy, if my estimates from the weather radar are correct (fig 1), and are aligned around 240-060°. Rainfall accumulations are not particularly high along its length for the period 08-21 UTC, generally between 8 to 16 mm with a few isolated light blue pixels indicating accumulations greater than 16 mm in Somerset. The first band of showers seems to fizzle out, as a second band forms a little further to the north for a short distance, before the southerly band re-intensifies somewhere over the Blackdown hills. The band of showers stretched as far as East Anglia before losing its coherence. We never got anything more than a few spots out of it here in Bradninch during the day, 14 km to the northeast of Exeter, and the cut off between wet and dry was quite sharp.
The recent flooding in Okehampton on the afternoon of the 30th of July was another good example of peninsula convergence, which the Met Office NWP model just didn’t seem to get a grip on. Has the occurrence of peninsular convergence increased in recent years, or is that just down to extra vigilance on my part?
For once there was an upper air ascent in the right place, and for the right time (fig 3). The wind direction aloft in the 11 UTC Camborne ascent are remarkably constant, between 240 and 260°, well up to 15,000 feet.
That brave chap Pen Hadow and his Arctic Mission team have now entered the Arctic Ocean proper, in fact they have now entered the Chukchi Sea on their journey north. You can follow the expedition by means of the Arctic Mission website. It’s a shame that they don’t seem to have an observer on board who can send out a SYNOP observation every six hours, although they reported that the air temperature at 10 UTC this morning was +3°C and they were around 67° north, so they still have a long way to go before they meet the ice edge at around 80° north.
Fascinating anomaly chart for the first two weeks of August 2017. A band of cold anomalies more or less stretches from central north America, across the north Atlantic, to northwest Europe, with anomalies ranging from zero to -2°C. The recent heatwave across southeast Europe has left its mark there, with a belt of positive anomalies, as warm as +6°C over the Ukraine and eastern Black Sea, and curving down through Iraq, Saudi Arabia and into Sudan.