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 Islands: The hottest months are usually June and September with an average temp of 80°F, while the coldest months are February and March with an average of 78°F. The rainiest months in San Blas Islands are October, August, July, and November, with each month seeing an average of 12 inches of rainfall.