HEAT 2023. Half of France is affected by this new heat wave and Météo-France is extending its heat wave vigilance to 43 departments from Tuesday 5 September. The forecasts.
[Mis à jour le 4 septembre 2023 à 16h24] The month of September starts with very hot weather over a large part of France. Météo-France places 43 departments on heatwave yellow vigilance this Tuesday, September 4, 2023. Forecasters estimate that the heat wave is likely to last a few more days with still degrees in the middle of the week, and peaks at 37 degrees locally. The mercury should remain high all week and Météo-France warns that “heat wave vigilance could be gradually extended to other departments”. The transition to a higher level of vigilance is not excluded also warns Météo-France.
This summer of 2023 was very hot, heat waves followed one another, and temperatures often exceeded seasonal averages. With the late and intense heat wave at the end of August, the summer of 2023 is now one of the hottest summers France has ever known. Météo-France also announced on Monday September 4 that it is the fourth hottest summer since 1900 after 2003, 2018 and 2022. This beginning of September confirms the trend, Météo-France warns, “we expect unprecedented temperatures for a month of September over a large south-west quarter”, and “no real refreshment (…) glimpsed before at least Sunday”
What are the heat wave forecasts for early September 2023?
The Météo-France yellow heat wave vigilance card
What is a heat wave?
As a reminder, we speak of a heat wave when these four characteristics are combined:
- a period of high heat;
- with temperatures five degrees higher than normal for the season;
- the day and the night ;
- for three consecutive days.
What is the heat wave plan put in place this year?
On June 8, 2023, the government announced the various actions implemented as part of its heat wave plan to protect the population during intense heat waves.
What are the recommendations to follow during the heat wave?
Heat wave, heat peak, heat wave and heat dome: what are the differences?
Heat wave and heat wave are two different things. To speak of a heat wave, the temperatures must be five degrees higher than normal for the season, day and night, and this for at least three days and three nights. The heat wave temperature threshold therefore differs according to the departments and regions. Heat waves most often occur in France in July and August. We must be vigilant from the month of June. High temperatures, even above seasonal norms, do not necessarily mean a heat wave. Most often, these are heat waves.
The term heat peak is more to be used during a sudden rise in temperature, while a heat wave corresponds to a longer episode. Météo France judges that a heat wave is in progress when temperatures above the monthly average are detected by more than three degrees Celsius, for at least three days.
Finally, heat dome is another term used. It settled over almost all of France in May 2022. This meteorological phenomenon is explained by a large mass of hot air from Morocco and Spain, trapped by atmospheric pressure. This usually occurs in summer, but also in spring. It results in scorching heat.
Météo France provides several levels of heat wave vigilance: level 1 (green) corresponds to a “seasonal watch”, level 2 (yellow) to a “heat warning” and it is level 3 (orange) which corresponds to “the ‘heat wave alert’. Finally, level 4 (red), the highest, determines “maximum mobilization”. In summer, it is not uncommon for several departments to be placed on orange or red alert for the heat wave.
Heat wave: what are the temperature records recorded in recent years?
If the heat wave of the summer of 2003 remains in everyone’s memory (and that of 1976 also among the old), France has since experienced other episodes of very hot weather. In summer 2019, several absolute temperature records were reached in different cities. According to data from Météo France, 50 cities had thus recorded a new record since July 25, 2019. While the summer of 2019 had been very hot, some records were broken during the heat wave of mid-June 2022. During the day heat wave of Saturday June 18, 2022: 150 municipalities broke a heat record, according to meteorologist Patrick Marlière, interviewed by BFM TV: “We went from 70 cities with broken monthly records, to more than 150 today in France, from the Pyrenees to the Belgian border”. The city of Nantes thus broke its record for the month of June with 39.1°C. In the South-West, records at more than 40 degrees have been reached: Biarritz with 42.9°, Saint-Jean-de-Luz with 42° or Bordeaux with 40°.
The July 2022 heat wave also set temperature records on Monday July 18. Of the 63 records recorded that day, the majority are in the north, west or southwest. We can cite :
- Beaulieu-sur-Layon (49): 42.7°C
- Biscarrosse (40): 42.6°C
- Nantes (44): 42°C
- La Roche-sur-Yon (85): 41.5°C
- Cholet (49): 41.3°C
- Niort (79): 41°C
- Rennes (35): 40.5°C
- Caen (14): 40.1°C
- Dinard (35): 40°C
- Saint-Brieuc (22): 39.7°C
- Noirmoutier (85): 38.7°C
- Lorient (56): 37.6°C
- Brest (29): 39.3
- The island of Yeu (85): 35.9°C
During the heat wave of August 2023, many records were also recorded. Among them :
- 43.2 degrees at Carcassonne on August 23;
- 43 degrees at Nyons on August 23;
- 42.9 degrees at Mirande on August 24;
- 42.7 degrees in Orange on August 22;
- 42.5 degrees in Saint Barthélémy-de-Vals on August 22;
- 42.5 degrees in Montauban and Agen on August 24;
- 42.4 degrees in Toulouse on August 23;
- 42.3 degrees in Nîmes on August 22;
- 42.1 degrees at Narbonne on August 23;
- 41.4 degrees in Lyon on August 24;
- 30.4 at Mont Aigoual on August 23.