September in Prince Rupert is the sunniest month of the year. In September, the weather in Prince Rupert is typically warm. Average daily high temperature in September is about 13 degrees above zero. On average, Prince Rupert has 22 rainy, 7 sunny, and 1 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 Prince Rupert.