After placing half of the country on heatwave orange vigilance, Météo-France placed four departments on red vigilance on Monday August 21. If the appearance of the red sticker this year is unprecedented, it is even more intriguing if we consider how late this heat wave is, arriving at the end of the summer season. By way of comparison, red vigilance was declared twice in 2022, once in June and again in July. We speak of a late heat wave in cases of delayed onset.
A heat wave is said to be late when it occurs after August 15, with the traditional heat wave period extending from June 15 to mid-August. This hot air mass came directly from North Africa and settled over the country creating a “heat dome” with high pressures that lock in heat over part of the country.
This late heat wave is however an extremely rare and recent event. Since 1947, when Météo-France began to scrutinize heat waves, only six of them have been considered late. All of them took place after the year 2000: in 2001, 2009, 2011, 2012, 2016, 2017. Unfortunately, it is not impossible that in the years to come, episodes of heat waves will be recorded before June 15th. We will then speak of early heat waves.
The affected departments will face temperatures that may approach 40 degrees in some cases, as well as warmer nights, with a minimum threshold around 20 degrees. According to Météo-France, it is “the hottest episode of summer 2023”, which will display an “exceptional duration and intensity at this time of year”. Severe thunderstorms are also expected when the heat dome collapses.
