Planning for the weather is an important factor for making your trip to Santarém a success, especially when you're splurging. The hottest months are usually September and October, with an average temperature of 29°C, while the coldest months are March and January, with an average of 26°C. The rainiest months in Santarém are March, April, February and May, with each month seeing an average of 570 mm of rainfall.