If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Mandeville: The hottest months are usually August and September with an average temp of 76°F, while the coldest months are February and January with an average of 72°F. The rainiest months in Mandeville are September, October, May, and August, with each month seeing an average of 10 inches of rainfall.