Record rains from the Pays de la Loire to the Paris Basin: why such rainfall?
The very rainy nature of the disturbance which circulated for nearly 24 hours on an axis going from Pays de la Loire to Belgium via the Paris Basin can be explained by the origin of the Kirk depression which flew over tropical latitudes. of the Atlantic with an air mass that is full of humidity. Most ocean disturbances that arrive in France form off the coast of Newfoundland and circulate over cooler seas, with less precipitable water. The extra-tropical depression Kirk retained a “warm core” until its arrival over France, which amplified the precipitation. In contact with the cooler air coming down from the British Isles, a very precipitating axis came to block for several hours in the same place.
Remarkable rain episode © The Weather Channel
Rainfall accumulations reached the equivalent of a month of rain. In Paris, with 70 millimeters, we even far exceed the average accumulation for October which is 55 mm. We have to go back more than a century (October 17, 1920 with 74 mm) to find daily rain of this magnitude in the capital.
Record rains from Pays de la Loire to the Ardennes © The Weather Channel
Floods and floods: a red alert for the Grand Morin in Seine-et-Marne
This episode of lasting rain is not without consequences on the hydrological network. As the soils are saturated following the rains of recent weeks, precipitation no longer infiltrates much into the soil. They flow towards watercourses or stagnate in the bottoms of valleys and agricultural plains which see real lakes forming within the plots. Seine-et-Marne, after an already exceptional episode of rain on September 27 (up to 100 mm in the Coulommiers sector), once again saw the equivalent of a month of rain fall during the day on Wednesday October 9 (50 to 70 mm). The Grand Morin was therefore placed on red alert on Wednesday afternoon by the Vigicrues organization in anticipation of an exceptional flood. This Thursday, October 10, the flood peak of the Grand Morin is record since the water level exceeds the reference flood of June 2016.
Record flood of Grand Morin © The Weather Channel
Flooding is widespread in the Grand Morin valley, in the heart of the large agricultural plateau of Brie. The town center of Coulommiers has its feet in the water.
Floods in Coulommiers (77) © The Weather Channel
An episode of strong wind which mainly affected the southwest and the center-east
It was with the arrival of the low pressure center Kirk that the winds strengthened significantly on Wednesday afternoon on the Aquitaine coast and the Pyrenean ridges. Gusts reached 109 km/h at Cap Ferret in Gironde, 120 km/h at Ciboure on the Basque coast. Inland, 111 km/h was recorded in Pau as well as a violent gust of 138 km/h in Peyrusse-Grande in Gers. In the Pyrenees, at the Iraty weather station very exposed to the south wind (1400 m), a very violent gust of 211 km/ha was observed. In the evening, it is the center-east’s turn to suffer violent gusts of southerly wind with 104 km/h in Puy-en-Velay, 107 km/h in Lons-le-Saunier and 113 km/h in Lyon-Bron. During the night, the strongest winds rose towards the northeast with up to 113 km/h in Mulhouse. These strong winds caused falling trees and damage to roofs in the areas most exposed to the wind.
Strong swells in the Atlantic and the Mediterranean
The south to southeast wind raised strong southerly waves on the Gulf of Lion. Off the coast of Marseillan in Hérault, 3 boats capsized, causing one victim and one seriously injured. In the Atlantic, sea conditions were particularly degraded in the southern part of the Bay of Biscay with a strong swell of 3 to 4 m from the west-southwest crossing the sea from the south wind, raising waves of 2 3 meters away.
The Kirk depression quickly evacuated towards Germany late Wednesday night into Thursday. However, the weather remained unstable in the north with a pattern of showers. The west and south-east of the country experienced drier weather. With all the rain having fallen, floods remain under close surveillance. Many rivers are under surveillance by the Vigicrues organization.
