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 San Agustin: The hottest months are usually January and February, with an average temperature of 18°C, while the coldest months are August and September, with an average of 17°C. The rainiest months in San Agustin are April, March, May and June, with each month seeing an average of 305 mm of rainfall.