- A widespread warming trend will set in from the Tuesday of the back-to-school week, following a cooler start to the week.
- Temperatures will steadily rise to a peak expected between Friday and Sunday.
- Temperatures of up to 36°C in the South are expected, particularly in Nîmes, and up to 34°C in Lyon.
- An official heatwave remains highly unlikely due to the longer nights at the beginning of September.
A Sudden Return of Sunshine and High Temperatures
After a late August marked by unsettled weather, locally severe thunderstorms, and a noticeable drop in temperatures, weather conditions are about to change radically across France. While the gloomy weather of recent days might have suggested an early transition to autumn, a much warmer and sunnier air mass is set to gradually establish itself across the entire country.
The cool, unstable air mass will give way to much warmer and sunnier weather from the very first days of September. This change in the weather will coincide with the return to school. Although a few lingering showers are still forecast this Monday in the north-eastern quarter of the country, with highs of between 20°C and 25°C in the northern half and up to 33°C along the Mediterranean coast, the improvement will be widespread by Tuesday.
Temperatures Rising Steadily Until the Weekend
As the days progress, temperatures will rise steadily. The widespread drying of the air will allow the sunshine to settle in for the long term. Thermometers will climb daily to reach very high levels for the season.
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Projections predict a temperature peak between Friday and Sunday, particularly pronounced in the southern half of the country. As the weekend approaches, the 30°C mark will be crossed in many regions. For Friday, forecasts show highs reaching 28°C in Paris, 29°C in Rennes, and 30°C in Strasbourg and Marseille. In the Centre-East and South-East, the heat will be even more intense, with temperatures reaching 34°C in Lyon and local peaks of up to 36°C, notably around Nîmes.
A Late Summer Spell but No Risk of a Major Heatwave
Although this episode will bring significant heat for the beginning of September, a distinction should be made between this rise in temperature and a classic heatwave. Indeed, the progression of the season plays a decisive regulating role in overnight cooling.
A true heatwave remains highly unlikely in September thanks to the lengthening nights, which promote nocturnal cooling. At this time of year, the shorter daylight hours allow the atmosphere to shed the excess heat accumulated during the day. As night-time temperatures remain moderate, official heatwave warning thresholds are unlikely to be met. While the signal for a return of hot weather is fully confirmed, specialists point out that the exact duration and final intensity of this spell still carry a margin of uncertainty.
