If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Santiago Atitlan: The hottest months are usually March and February, with an average temperature of 24°C, while the coldest months are December and January, with an average of 23°C. The rainiest months in Santiago Atitlan are September, May, June and October, with each month seeing an average of 570 mm of rainfall.