Thibault Guinaldo is a researcher in space oceanography at the Center for Satellite Meteorological Studies in Lannion, affiliated to the National Center for Meteorological Research (Météo-France/CNRS). He returns to the characteristics of the current ocean heatwave and what is being observed near the French coast.
Thibault Guinaldo: We are facing something extraordinary. Reliable data has been available since 1981 thanks to satellite measurements, and we have never seen readings like this. Throughout the North Atlantic Basin, temperature anomalies reach 1°C, in certain areas up to 5°C, particularly near the British Isles. This is quite impressive, especially since we are not expecting any cooling at the moment and we are at the beginning of summer.
This heatwave is particularly observed around the British Isles. Does it also occur near the French coasts?
As far as Brittany waters are concerned, two different situations can be observed. The English Channel is fairly preserved thanks to its strong currents, although we saw last year that the high temperatures could warm certain areas. In the south, on the other hand, the Bay of Biscay shows a stronger warming tendency and is currently recording values that could also be observed in mid or late summer. It stands out well on the map. As in the Mediterranean Sea, a category 1 or 2 sea heat wave occurs, especially between Corsica and Spain.
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Can the situation observed further north spread or herald a similar situation elsewhere?
It is possible for exchanges to occur between two zones, but this is unpredictable. What is certain, however, is that if the conditions on the French plain remain the same – stagnant high pressure, low mixing and high temperatures – the surface temperatures will rise and the heat wave in the Gulf of Gascony will intensify. We are counting on that with the forecasts for the next few days. For the medium-term dynamics across the entire catchment area, things are more complicated. If the weather conditions change, the situation may change.
We remember the Mediterranean Sea Heatwave in 2022. Is it surprising that much larger areas with strong currents are affected?
The Mediterranean Sea is the case in point. An area with few tides and little water mixing favors water stratification: there is a layer of warm water above the cold water. This surface isolates itself, resulting in fewer swaps. It is therefore exceptional to observe this phenomenon over several days in the currently affected areas in the Atlantic, where mixing is more pronounced.