August in Grafton is the sunniest month of the year. In August, the weather in Grafton is typically warm. Average daily high temperature in August is about 21 degrees above zero. On average, Grafton has 23 sunny, 5 rainy, 2 partly cloudy, and 1 cloudy day in August. The rains are usually moderate. August as well as July and September is considered the most comfortable time to visit Grafton.