August in Santa Rosa is the sunniest month of the year. In August, the weather in Santa Rosa is typically warm. Average daily high temperature in August is about 17 degrees above zero. On average, Santa Rosa has 21 sunny, 5 rainy, and 5 partly cloudy days in August. The rains are usually light. August as well as {{month_nom: February}}, and {{month_nom: February}} is considered the most comfortable time to visit Santa Rosa.