July 1, 2022

Weather Alert: Strong west wind, heavy rain

Through Regis CREPET, meteorologist

STRONG WIND AND HEAVY RAIN ALERT

Complete weather forecasts live by phone at

3201*

From Monday December 27 at 6:00 p.m. to Wednesday December 29 at 12:00 p.m.

Situation

In a context dominated by low pressures over western Europe, a low pressure called Ronald circulates in the English Channel until Tuesday evening.
As it passed, it caused a strong gust of wind near the Atlantic, with gusts reaching 80 to 90 km / h, up to 100 to 110 km / h on exposed capes and coast and 70 to 80 km / h in the lands. At sea, waves of 4 to 6 m are expected off the Breton coast, up to 7 to 8 m between the island of Oléron and the Gironde. Due to low tidal coefficients (47 and 50), the risk of coastal submersion at the time of high tide will be low. The strong gale on Tuesday concerns the coast of the Channel, especially from Seine-Maritime to the Opal Coast with gusts between 90 and 110 km / h.

This disturbance also causes abundant rains on the west of the Massif Central and Limousin by blocking effect on the reliefs: thus, the conjunction of these rains and the melting of snow in mid-mountain areas may cause some hydrological reactions. But the flood thresholds will not be reached, due to the dry weather of the last two weeks and the current low level of the rivers. This disturbance will also be blocked on Tuesday in the Alps with rain up to 1700 m altitude.

Observation

This Monday

At 6 p.m .: the new oceanic disturbance arrives along the Atlantic Arc with sustained rains and stronger wind. It is in the evening and early night that the gusts are strongest, mainly between the Loire estuary and the north of the Gironde, with gusts reaching 80 to 90 km / h, and gusts expected to 100 / 110 km / h on exposed peaks.

At 12h00, the low is still positioned to the south of Ireland at 982 hPa. For the moment, it is generating moderate to fairly strong west-southwest winds on Pointe Bretonne with gusts between 60 and 80 km / h on the exposed capes and islands. Further south, gusts are often between 40 and 50 km / h. A gust of 70 km / h was recorded in Royan.
Regarding precipitation, over the last six hours, it has fallen on average from 5 to 20 mm in the departments on yellow alert. In particular, there were 17.3 mm at Tulle (Corrèze) and 18.7 mm at Voutezac (Corrèze).

At 9:00 a.m., the low at 981 hPa is located in the south of Ireland. The wind is gradually strengthening on the Atlantic coast with gusts between 50 and 60 km / h and up to 70 to 80 km / h on the exposed capes.

Evolution

This Monday evening, thehe strong wind is spreading throughout the west of France. It is near the coast, especially between the Loire estuary and the north of the Landes that the wind blows the strongest, with gusts between 80 and 90 km / h. Peaks of up to 100 km / h are possible on the capes and exposed coasts of the Charente coast. Inland, the southwest wind strengthens to 80 km / h between the Bordeaux region, Poitou, Charentes and Anjou.

In the night of this Monday to Tuesday, the strongest winds are observed over the entire Atlantic coast, with gusts of up to 80 to 90 km / h and locally 100-110 km / h, still mainly on the Vendée and Charente coast and the north of the Gironde. Inland, the wind reaches 80 km / h in Poitou-Charentes, north of Limousin to the Center-Val de Loire region. In Brittany, it’s the opposite, the wind is weakening.

Tuesday morning, the wind weakens slowly near the Atlantic and over western France. It is reinforced between Seine-Maritime and the Opal Coast with gusts between 90 and 100 km / h both on the coast and inland.

Tuesday afternoon, the wind blows particularly strong in the early afternoon on the Opal Coast and the North Sea, with gusts exceeding 100 to 110 km / h on the coast and 80 to 90 km / h inland. The wind gradually calms down in the evening. It is advisable to be wary of the possibility of stronger gusts than expected, close to 120 km / h in the Boulonnais.

This gust of wind is accompanied by continuous rains of moderate intensity. Coming to block on the west of Auvergne, the orographic effect will play in full and the rains will persist from Monday morning to Tuesday afternoon. Then, from Tuesday afternoon to Wednesday morning, these rains will strengthen over the central Alps, also blocking by orographic effect. Throughout this episode of bad weather, the rainfall amounts will become important. Locally, they can reach 100 mm, which corresponds to three weeks of precipitation. Thus, the conjunction of these rains and the melting of snow in mid-mountain ranges may cause some reactions from the streams, but the flood thresholds will undoubtedly not be reached, despite a few occasional overflows.

To sum up, this episode of bad weather which will end on Wednesday morning will be responsible for a fairly marked gale, but usual in autumn and winter. The accumulations of rains will be significant from Monday morning to Tuesday afternoon in the west of the Massif Central, without causing any risk of damaging floods, apart from a few occasional overflows which should remain relatively limited. In this regard, the rivers from the west of the Massif-Central, in particular the Dordogne and its tributaries, seem to be the most exposed to a risk of high flow and some overflows.

List of departments concerned