In this month of June 2023, the sea reaches high temperatures along the coasts of Brittany. Temperatures are sometimes 3°C higher than seasonal norms.
In this month of June 2023, the heat is strong in Brittany. On Saturday 17th and Sunday 18th June, the air temperature could rise to 30°C to 32°C between Rennes and Ancenis, and 27°C in Guingamp for example.
The temperature of the sea is not to be outdone, driven by the strong heat of May and June. Steven Tual, the weather forecaster at Météo Bretagne, explains this phenomenon to Echo de l’Armor et de l’Argoat.
“Temperatures that we normally reach only in August”
“Currently, the water temperatures by the sea are very high on the coast of Brittany. They show +1 to +3°C compared to normal depending on the sector. These are temperatures that we normally reach only in August, “adds the meteorologist.
Thus, the sea could reach 20°C in La Baule this weekend, 18°C between the bay of Saint-Brieuc and the Emerald Coast, as well as in the bay of Douarnenez. And on the Atlantic coast, between 18 and 19°C.
How can these abnormally high temperatures be explained? “It’s a phenomenon that we find throughout the North Atlantic at the moment. The very stable weather conditions, very anticyclonic, favoured the absence of sea currents and therefore the warming of all surface waters. »
Conditions accentuated in Brittany by exceptional sunshine in May and June. Thus the town of Plovan in the bay of Audierne in the south of Finistère was the sunniest town in France in May, with 304 hours of sunshine in total!
“We bathe as if we were already there in August”
Some sectors are therefore more affected by this warming than others. “On the wild coast, between southern Finistère, the bay of Audierne, the country of Lorient, up to the edge of the Gulf of Morbihan, we have very significant anomalies, with temperatures 3°C above the norm. We bathe there as if we were already in August, with water temperatures between 18 and 19°C. ”
In the bay of Saint-Brieuc, we are also approaching 18°C, a level 2°C higher than normal. “Normally in Brittany, the water temperatures reach their maximum between mid-August and mid-September, and not in June”, specifies Steven Tual.
The winds, which often blew in the same northwest direction, also slowed the creation of sea currents, and therefore “the rise of deeper waters, and therefore colder on the surface. A phenomenon called upwelling, and which therefore happened very little this year in Brittany”.
Worrying warming for biodiversity
If this phenomenon of warming of the seas is pleasant for swimmers, “it is more worrying for underwater life and biodiversity”, explains Steven Tual.
Studies on these marine heat waves have shown that a sea water temperature well above normal over a long period has the same consequences as a forest fire on land.
This leads, for example, to a return of green algae in the bays of Brittany, a higher number of jellyfish, or even marine species that find themselves under tension. “All over the North Atlantic, we have crazy anomalies. And even around the world, the temperature of the seas and oceans is increasing. It is very worrying. These are the consequences of pollution and climate change, unfortunately, ”warns Steven Tual, meteorologist forecaster at Météo Bretagne.
