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 Mendrisio: The hottest months are usually July and August, with an average temperature of 20°C, while the coldest months are January and February, with an average of 4°C. The rainiest months in Mendrisio are November, August, May and October, with each month seeing an average of 196 mm of rainfall.