Weather is probably a major factor when you plan your trip to San Luis, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually September and October with an average temp of 83°F, while the coldest months are February and March with an average of 80°F. The rainiest months in San Luis are October, November, June, and July, with each month seeing an average of 12 inches of rainfall.