September in Cotonou is the rainiest month of the year. In September, the weather in Cotonou is typically warm. Average daily high temperature in September is about 27 degrees above zero. On average, Cotonou has 28 rainy, 1 sunny, and 1 cloudy day in September. The rains are usually heavy. September as well as March, May, June, and July is considered the most uncomfortable time to visit Cotonou.