Weather is probably a major factor when you plan your trip to Santarém, 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 84°F, while the coldest months are March and January with an average of 79°F. The rainiest months in Santarém are March, April, February, and May, with each month seeing an average of 22 inches of rainfall.