Barely two weeks after a historic heatwave marked by its intensity never seen before on August 15 (>>), France finds itself once again affected by abnormal heat, this time at the beginning of September. Now that meteorological autumn has begun (since September 1), the country is facing a anticyclonic blocking conducive to very strong lasting heat and sometimes never observed in September, this since the day of September 4.
The very last days of August were under the influence of much more gloomy weather, since no station had reached 30°C in France on August 28, 29 and 30. From now on, this high heat threshold (30°C) has been crossed on more than 60% of the territory’s stations continuously since Monday 4with a peak at 77% this Saturday. These are even 18% of stations (nearly 1/5 of the country) which has reached the bar 35°Ca remarkable situation past the heart of summer.
With a national thermal indicator of 25.1°C on September 4 and 9 (average of minimum and maximum temperatures over 30 stations), these are quite simply the two hottest days observed in France since the post-war period (start of data series for this indicator). In fact, the indicator had never exceeded 25°C in September!
Share of French territory affected by high and very high heat at more than 1,700 Météo-France stations
In addition to the late nature of this hot sequence, the exceptional side stands out by the regions which are affected. It is not about the Mediterranean sectors or even the South of Aquitaine, but above all the Central regions where 35 to 38°C have been exceeded, i.e. most often the highest temperatures observed during this year 2023. This is also the case for Pariswith the 35°C exceeded for the first time in 2023 on September 8 and 9 !
Among the main resorts, from September 4 to 9, 35°C is exceeded as far as Brittany, Val-de-Loire, the Paris region and even at the gates of Normandy. On September 4, the thermometer panics with up to 36.3°C in Bourges, 37.0°C in Poitiers or even 37.3°C in Angoulême. On the secondary network, the values were even more exceptional during the same afternoon of Monday September 4, exceeding the 38 to 39°C in Poitou and Indre: up to 39.0°C in Blanc (Indre) and 39.3°C in La Trimouille (Vienne).
Ranking of maximum temperatures observed from September 4 to 9 on the Météo-France main network
Such values are levels never seen before for the month of September. These are therefore hundreds of monthly heat records who are beaten, sometimes several consecutive days, and this on stations with data series of several decades… or even centennials as for Poitiers (1921) or even at Bourget (1920).
The gap between the old and new records sometimes rises beyond +1.5 to +2°C, witness to the historic intensity of this heat wave. A gain that reaches +1.6°C in Poitiers (going from 35.4°C to 37.0°C), or even +3.2°C in Saint-Brieuc (going from 28.3°C to 31.5°C).
Monthly heat records broken from September 4 to 9 on the main Météo-France stations
Maximum temperatures observed from September 4 to 9, 2023 – Weather-Cities
And like during last month’s heatwave, this heat is also nocturnalIt is. Des tropical nights (>20°C) particularly in the heart of cities for several days, and records were broken by the shovel for a month of September in many regions, as in Occitania (Toulouse, Agen, Rodez), Brittany (Quimper), Auvergne-Rhône-Alpes (Lyon, Puy-en-Velay, Aurillac), Pays de la Loire (Nantes, Angers), Normandie (Rouen) and Hauts-de-France (Saint-Quentin).
In the heart of the capital, the thermometer did not fall below 25.5°C at Paris-Lariboisière station (10th arrondissement) during the night of September 8 to 9, marker of a very important urban heat island (daytime heat accumulated on buildings, then released during the night, limiting the drop in temperatures).
Monthly records for high nighttime temperatures broken from September 4 to 9 on the stations of the Météo-France main network
But the most notable fact remains for the Montauban station. Opened in the 19th centuryshe observed the mildest night ever observed in all months combined with 24.4°C at least warm during the night of September 3 to 4 ! An incredible event in September, whereThe nights are significantly longer than at the beginning of summer (duration of the night 11 hours at the beginning of September compared to 8:30 at the end of June)!
Absolute record high minimum temperature in Montauban – night of September 3 to 4, 2023
Minimum temperatures observed from September 4 to 9, 2023 – Weather-Cities
This heat wave will continue this Sunday 10, before a intrusion of more oceanic air from the West from Monday 11. From Tuesday 12, the storms will return (sometimes strong)officially putting an end to this very hot streak.
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