If you’re hoping to get lost in the rain on your romantic getaway, check out these details about year-round temperatures in Mercallo: The hottest months are usually July and August with an average temp of 69°F, while the coldest months are January and February with an average of 39°F. The rainiest months in Mercallo are November, October, May, and August, with each month seeing an average of 8 inches of rainfall.