The heatwave France has prepared for all weekend has arrived, with Meteo France issuing its first high-temperature weather warning for five departments days ahead of the "canicule's" peak.
The national forecaster has placed Paris, as well as the 'petite couronne' departments of Hauts-Seine, Seine-Saint-Denis and Val-de-Marne, and Seine-et-Marne on orange 'canicule' alert, describing conditions as "a heatwave episode of remarkable intensity, especially for early summer".
In its early bulletin on Monday, Meteo France said that overnight temperatures in Paris had dipped no lower than 20C.
As reported, a high-pressure system has raced into France from the Sahara, with heat quickly spreading north. By midday on Monday, temperatures will have hit 34C in parts of Allier and Var, while the mercury is expected to hit 32C in Paris by 2pm. Across most of France, temperatures on Monday will be between 30C and 34C. Forecasters said that Manche, Brittany and Pays de la Loire will avoid the highest temperatures.
After a sultry evening, with forecast temperatures no lower than 23C in Paris, 24C in Lyon, and 29C in Menton, the heat will rise quickly on Tuesday, reaching 36C in Strasbourg and 37C in Nancy as the high pressure system moves east. Across France, forecasters expect temperatures to average between 30C and 35C.
The mercury is expected to pass 40C across most of the country on Wednesday, Thursday and Friday, Meteo France said. Temporary respite is available in Finistère, where it will be a pleasant 23C to 26C on Wednesday.
On both Thursday and Friday, the average 24-hour temperature in 30 cities of France used to calculate the indicateur thermique national will exceed 28C for the first time since the deadly 2003 heatwave. In that year, the average 24-hour temperature was more than 28C for a full week.
The good news is that forecasters expect the peak of the heatwave to last just two days, with cooler air heading into the country from the west. But, while temperatures will fall, Meteo France said they will remain above normal for the time of year.
Sales of fans and air conditioning units have shot up by as much as 400% in some parts of France, as residents prepare for the heatwave - but experts have warned people to take care with their use.
The temptation is to turn on the 'clim' to make rooms as cool as possible to bring relief from the heat outside, but experts said too great a temperature difference between inside and outside could cause health problems, from rhinitis and sinusitis - to angina.
Air conditioning, experts say, should be used in moderation. The Agence française de sécurité sanitaire environnementale (AFSSE) said in 2005 that the best first course of action in hot weather is to close windows and shutters during the day and only open them at night when the air is cooler. Hanging wet clothes on open windows in the evening will also cool the air.
To avoid health issues, the ideal temperature difference between interior, air-conditioned temperatures and the outside heat should be no more than 8C, experts said.
"When the air conditioning is too cold, when it is between 30 and 35C outside, you impose violent temperature changes on your body. The body no longer understands what is happening to it, and our organs want to defend themselves," Jean-Louis San Marco, Professor of Medicine at the University of Marseille, told Allô Docteurs.
"When it is hot, the blood vessels [in our nose, in our throat] dilate to help the body eliminate excess heat. On the contrary, when it is cold, they contract to keep it.
"When we move too often from hot to cold, our mucous membranes get irritated."
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