Other facts from our historical weather data: When is the rainy season in Coos Bay? Rainy season in Coos Bay occurs in the months of January, February, March, November and December. Does Coos Bay have a dry season? Yes, the months of July and August are very dry. Which is the warmest month in Coos Bay? August has an average maximum temperature of 20°C (68°F) and is the warmest month of the year. Which is the coldest month in Coos Bay? The coldest month is December with an average maximum temperature of 11°C (52°F). Which is the wettest month in Coos Bay? December tops the wettest month list with 298mm (11.7 in) of rainfall. Which is the driest month in Coos Bay? July is the driest month with 13mm (0.5 in) of precipitation. No idea where to travel to this year? We have a tool that recommends destinations based on your ideal conditions. Find out where to go with our weather planner.