If you’re looking forward to lots of outings with your partner, take a look at these details about year-round temperatures in Rio Branco: The hottest months are usually September and August, with an average temperature of 27°C, while the coldest months are July and June, with an average of 25°C. The rainiest months in Rio Branco are March, February, January and December, with each month seeing an average of 341 mm of rainfall.