If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in San Blas: The hottest months are usually May and June with an average temp of 81°F, while the coldest months are January and February with an average of 73°F. The rainiest months in San Blas are August, September, July, and October, with each month seeing an average of 10 inches of rainfall.