If you're hoping to get lost in the rain on your romantic getaway, take a look at these details about year-round temperatures in San Blas Islands: The hottest months are usually June and September, with an average temperature of 27°C, while the coldest months are February and March, with an average of 26°C. The rainiest months in San Blas Islands are October, August, July and November, with each month seeing an average of 310 mm of rainfall.