September in Rjukan is the sunniest month of the year. In September, the weather in Rjukan is typically cold. Average daily high temperature in September is about 9 degrees above zero. On average, Rjukan has 11 rainy, 7 sunny, 7 cloudy, and 5 partly cloudy days in September. The rains are usually heavy. September as well as April, May, June, and July is considered the most uncomfortable time to visit Rjukan.