If you're looking forward to lots of outings with your partner, check out these details about year-round temperatures in San Juan de Pasto: The hottest months are usually September and August with an average temp of 62°F, while the coldest months are August and July with an average of 62°F. The rainiest months in San Juan de Pasto are April, March, May, and November, with each month seeing an average of 18 inches of rainfall.