In September, the weather in Aix-en-Provence is typically warm. Average daily high temperature in September is about 25 degrees above zero. On average, Aix-en-Provence has 14 sunny, 8 partly cloudy, 7 rainy, and 1 cloudy day in September. The rains are usually heavy. September as well as June, July, and August is considered the most comfortable time to visit Aix-en-Provence.