If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Rivas: The hottest months are usually April and May with an average temp of 82°F, while the coldest months are January and February with an average of 80°F. The rainiest months in Rivas are October, September, June, and August, with each month seeing an average of 11 inches of rainfall.