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 Carlos: The hottest months are usually March and April, with an average temperature of 26°C, while the coldest months are January and December, with an average of 26°C. The rainiest months in San Carlos are October, November, September and August, with each month seeing an average of 340 mm of rainfall.