Weather is probably a major factor when you plan your trip to Rio Branco, and keep in mind that cheaper options are usually available when the weather isn't as good. The hottest months are usually September and August with an average temp of 81°F, while the coldest months are July and June with an average of 77°F. The rainiest months in Rio Branco are March, February, January, and December, with each month seeing an average of 13 inches of rainfall.