Twenty-eight departments in a large western half of the country, from Nouvelle-Aquitaine to Ile-de-France, are still on orange alert for thunderstorms on Sunday September 17 in the evening, an “intense” episode being feared with hail, gusts of wind and torrential rain in places.
Tristan Amm, forecaster at Météo-France, explained to Agence France-Presse to expect “storms which (should) begin to form from New Aquitaine during the afternoon. » “They will go up to Normandy until the middle of the night, passing through Centre-Val de Loire and Ile-de-France,” he detailed.
“These will be intense thunderstorms. We can expect hail, significant lightning strikes, wind gusts that can exceed 100 km/h, and rain that can seem torrential, quite brief most of the time,” he said. added. Météo-France forecasts up to 40 millimeters of precipitation per hour.
The national meteorological institute had placed 33 departments on orange alert on Sunday, from New Aquitaine to Normandy via Ile-de-France. There were still 28 left after 8 p.m., but France will not be done with storms yet.
“The situation is unstable across the entire country which is affected by a mass of warm and humid air very conducive to the formation of thunderstorms”, when the hot air “butts up with the colder air above” , explained Mr. Amm.
During the night from Sunday to Monday, "there will be other storms which will form and come up from the Mediterranean via Provence-Alpes-Côte-d'Azur, the lower Rhône valley, the Massif central to Alsace,” continued the Météo-France forecaster.
On Monday, twelve departments located in Normandy, Ile-de-France, as well as Drôme and Ardèche will be on orange alert due to storms. These last two departments will also be on orange rain-flood alert.
“From the end of the night from Sunday to Monday and during the day on Monday, a new rainy-stormy episode will affect the east of the Cévennes as far as the Drôme. Heavy stormy precipitation in a short time is likely,” specifies Météo-France, which expects cumulative rainfall of 80 to 100 millimeters.
On Saturday, the department of Hérault, placed on red alert for rain and floods, recorded very significant amounts of precipitation, which led to the closure of a railway line, while several roads were cut.
This episode notably caused flooding in the town of Lunas, in the north of the department, where the flood of the Orb swept away "several cars" and flooded "several houses in a hamlet located on the edge of the river", without causing any casualties, the mayor of the town, Aurélien Manenc, who is also a firefighter, told AFP.
In Mayenne, a mini-tornado formed on Sunday, around 6 p.m., near Ernée, damaging several buildings which collapsed without causing any casualties, we learned from the departmental fire and emergency operational center. relief.
Temperatures remained well above seasonal norms on Sunday, while France last week beat its record for a month of September, which dated from 1949.
It is “complicated” to make a direct link between global warming and storms, notes Tristan Amm. However, a warming air mass contains more water, implying a “greater” precipitation potential. “With warmer air, rainy episodes will be on average more intense and more catastrophic in the future,” summarizes the forecaster.