August in Sunbury is the rainiest month of the year. In August, the weather in Sunbury is typically warm. Average daily high temperature in August is about 11 degrees above zero. On average, Sunbury has 13 rainy, 12 partly cloudy, 4 sunny, and 2 cloudy days in August. The rains are usually moderate. August as well as June, July, and September is considered the most uncomfortable time to visit Sunbury.