August in Coos Bay is the warmest month of the year. In August, the weather in Coos Bay is typically warm. Average daily high temperature in August is about 18 degrees above zero. On average, Coos Bay has 17 sunny, 13 partly cloudy, and 1 rainy day in August. The rains are usually light. August as well as July and September is considered the most comfortable time to visit Coos Bay.