If you’re looking forward to lots of outings with your partner, check out these details about year-round temperatures in San Isidro: The hottest months are usually May and June with an average temp of 82°F, while the coldest months are February and January with an average of 77°F. The rainiest months in San Isidro are December, September, July, and October, with each month seeing an average of 15 inches of rainfall.