If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Santander: 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 80°F. The rainiest months in Santander are July, September, October, and August, with each month seeing an average of 15 inches of rainfall.