Saint-Malo is bracing for a genuine storm, with forecasters warning that a severe low-pressure system will slam into the Breton coast by Friday.
Tuesday brings an irregular, disturbed westerly flow, driven by a low of 1006 hPa tracking from Normandy down towards southern England. Expect a cloudy morning with light rain or showers, clearing in the afternoon as drier conditions and sunny breaks return. Winds will run west-northwest at 15 to 25 km/h in the morning, strengthening to westerly 20 to 30 km/h with gusts of 40 to 45 km/h by afternoon. Temperatures sit between 11°C and 15°C.
Wednesday turns properly unsettled. A cold front clears through overnight, ushering in a very active following flow with strong westerlies. Sunny spells will alternate with cloud, showers and heavy gusts, winds reaching 40 to 45 km/h with gusts between 70 and 90 km/h in squalls. Rain is highly likely, with a 90 percent chance of precipitation.
Thursday sees a disturbed south to southwest flow ahead of a low deepening rapidly out in the Atlantic. By midday UTC it sits 400 nautical miles west of the Brittany coast at 987 hPa. Morning cloud and sunny breaks give way to a heavily overcast afternoon, with light rain developing by evening as the wind builds further.
Then things get serious.
Overnight Thursday into Friday, that low keeps deepening, dropping to 977 hPa over Cornwall by the middle of the night before tracking along England's south coast through the early hours and morning. Saint-Malo and the north Breton coast will see a southwesterly flow turn tempestuous and westerly between midnight and Friday morning.
Friday morning is when the storm peaks. Wind swings to the west amid a highly unstable airmass within an active trailing system, blowing 55 to 60 km/h with maximum gusts between 100 and 120 km/h. Forecasters say the exact wind strength still needs refining this far out, three days from the event. Through Friday afternoon, as the low pulls away, winds ease, with westerly gusts of 80 to 100 km/h in the early afternoon dropping to 70 to 80 km/h by day's end.
Saturday remains unsettled but less violent than the day before. Average winds sit at 30 to 35 km/h with gusts around 60 km/h, sunny breaks mixed among shower clouds in the morning before more rain arrives in the afternoon. Sunday stays changeable too, with west to northwest winds strong at 40 to 50 km/h and gusts of 70 to 80 km/h under squalls.
For a fleet gearing up to cross the Atlantic solo, it's a forecast that will shape start-day thinking considerably. It comes just as the Saint-Malo race village opened its gates after a four-year wait, with skippers already weighing the demands of the festivities against the far bigger test now bearing down from the Atlantic.
