If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Chencun: The hottest months are usually July and August with an average temp of 84°F, while the coldest months are January and December with an average of 64°F. The rainiest months in Chencun are June, May, August, and September, with each month seeing an average of 13 inches of rainfall.