September in Reykyavik is the rainiest month of the year. In September, the weather in Reykyavik is typically cold. Average daily high temperature in September is about 9 degrees above zero. On average, Reykyavik has 27 rainy, 2 sunny, and 1 partly cloudy day in September. The rains are usually heavy. September as well as January, February, March, and April is considered the most uncomfortable time to visit Reykyavik.