Temperatures are expected to be 5 or 6 degrees above the seasonal norm, with highs of 27˚C in the north of the country and 29˚C in the south later this week.
Newspaper France Soir reported that a strong anticyclone over central Europe was bringing warm air from the south.
By September 24th, average temperatures in France for the month had reached 18.9˚C. This was the same as the average for the whole of July, which was the coldest July for 30 years.
This week's higher temperatures mean the September average will likely be warmer than July, making it the warmest September for at least 25 years.
The weather could be good news for the many French people who still have holiday to take before the end of the year. A survey by easyvoyage.com found that 88 percent of the French have not yet used all their holiday entitlement.