If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Cairndow: The hottest months are usually July and August with an average temp of 53°F, while the coldest months are January and February with an average of 36°F. The rainiest months in Cairndow are October, December, November, and January, with each month seeing an average of 9 inches of rainfall.