Change is already underway after a hot week with temperatures in the high 20sC/ low 30sC . There have been thunderstorms and the synoptic pattern is shifting. 23C the high tomorrow rather than 33C
And so, the bizarre September heatwave comes to an end. The longest September UK heatwave on record with seven days of 30+C in a row. The NHS reported a fivefold increase in people seeking heat exhaustion advice on their website. Page visits surged by 552% last week, peaking on Thursday 7th when their online page received one visit every 8 seconds. It was hot by day and very warm by night.
Sunday 10th Sept thunderstorms (colourful dots are lightning strikes, sferics) on Netweather Radar
Cambridge saw 32.5C on Sunday and Kew Gardens saw the highest temperature of the year with 33.2C on Saturday 9th. Should we say “the highest temperature of the year, SO FAR”? Cooler and fresher conditions are taking hold from the northwest and we’ve seen hefty downpours and thunderstorms to interrupt the sunshine. There could be another pulse of warmth next weekend but as we slip further into September, passing 33C again seems unlikely.
24-hour rainfall totals from UK Radar data.
The UK's highest temperature record for the month is from September 1906 which occurred in a momentous spell of great heat over a century ago.
Bawtry, Hesley Hall (South Yorkshire) recorded 35.6 on the 2nd Sept 1906. Hawarden Bridge (Flintshire) saw 32.3C and Gordon Castle (Moray) saw 32.1C the day before, on the 1st. Armagh also saw its record on the 1st of that year with 27.6C but that looks to have been broken in this heatwave.
“Castlederg in Northern Ireland has recorded a provisional temperature of 28.0 °C - if confirmed, this will make it Northern Ireland's hottest September day on record. Met Office.”
Ireland saw many station records broken and reached 28.9C in Co. Meath, not far off their 1906 record of 29.1C
Scotland came close to breaking its September nighttime highest minimum record of 18.7C. Aultbea had a very warm night last week where the temperatures stayed up at 18.5C, not what you might expect in the Highlands at this time of year.
Southern Britain saw Tropical Nights, where the temperature stays above 20C, which you would usually associate with the height of summer, not early Autumn.
The Netherlands, France and Belgium saw new September highest minimum temperatures on record 21.1C Vlissingen, Villacoublay 22.6C and 21.9C Zeebrugge respectively in the same heatwave.
France saw seven consecutive days of 37+C, never mind our 30+C and there were many local station records broken across France, Germany, Austria, Norway and the UK.
The push of heat up through France, from the western Mediterranean to the UK stayed in place due to an Omega block setup. Taken from the shape of the Greek letter Omega, there was a surface low over Spain which brought heavy rains to Iberia and flooding in Madrid on the 4th. It also helped to fling Saharan dust up through western Europe which coated many cars here in the UK. (Give it a good rinse off with a hose, if you are not still under a ban. Do not attempt to sponge off the abrasive sand)
Whilst some parts of Europe sweltered in the heat pushing north within the central High pressure of the Omega shape, the eastern end of the Mediterranean was hit by torrential rains. A significant surface low, Storm Daniel raged for days over Greece before edging southwards. It developed tropical characteristics which led to the unofficial label of ‘Medicane’, a Mediterranean hurricane. It reached Libya and the Benghazi region also saw devastating flooding and wild conditions.
Storm Daniel WorldView NASA
The near-stationary system brought reports that the record of the highest daily accumulated rainfall in central Greece had been broken. 754 mm falling in Pelion in just 18 hours. The previous record of 644.7mm was recorded in Kefalonia during the Mediterranean Cyclone Ianos in September 2020.
Volos was particularly badly hit with roads washed away, drinking water supply wrecked and vehicles swept away as mud covered the landscape. The high rainfall totals for Greece had shown up well on forecast models but the impacts were still severe. Istanbul in Turkey was also affected by destructive flash flooding.
This locked-in Omega Block set-up wreaked havoc for Greece and kept the heatwave conditions across France and parts of the UK. Slowly this week things change. A cold front will make its way down from northern Europe as high pressure tries to build in behind. A small Atlantic low nips across the UK midweek and then the frontal boundary to the south begins to push northwards.
For Monday, temperatures in southern Britain will still reach 23 to 27 or 28C. Rural Scotland could see a grass frost on Monday night but SE Britain remains warm. By Tuesday, the residual heat will have faded again, perhaps a high of 23C for the far south, in a more northerly flow. Tuesday will be cooler still.
The frontal rain will reach the Irish Sea, northern England and the Scottish Borders by Monday evening, introducing the fresher conditions from the northwest. Ahead of this in the warmer, more humid air, there will be a few showers, even a risk of thunderstorms. THE UKV shows something for eastern England by this evening but not as widespread as on Sunday. The Great North Run got a soaking on Sunday and Lincolnshire saw some tremendous storms to end the weekend.
Early on Tuesday, there could be a few showers reaching SE England from the Channel. The frontal band will have reached southwest England up to the Wash with heavier bursts for East Anglia by lunchtime and again the risk of heavy showers or thunderstorms developing in the last of the heat.
