May in Rennes is the rainiest month of the year. In May, the weather in Rennes is typically warm. Average daily high temperature in May is about 16 degrees above zero. On average, Rennes has 18 rainy, 7 sunny, and 6 partly cloudy days in May. The rains are usually moderate. May as well as January, February, November, and December is considered the most uncomfortable time to visit Rennes.