September in Sunbury is the windiest month of the year. In September, the weather in Sunbury is typically warm. Average daily high temperature in September is about 14 degrees above zero. On average, Sunbury has 12 rainy, 7 partly cloudy, 6 sunny, and 5 cloudy days in September. The rains are usually moderate. September as well as June, July, and August is considered the most uncomfortable time to visit Sunbury.