If you're looking forward to lots of outings with your partner, check out these details about year-round temperatures in San Agustín: The hottest months are usually January and February with an average temp of 65°F, while the coldest months are August and September with an average of 63°F. The rainiest months in San Agustín are April, March, May, and June, with each month seeing an average of 12 inches of rainfall.