If you’re looking forward to lots of outings with your partner, check out these details about year-round temperatures in Porto Velho: The hottest months are usually September and August with an average temp of 82°F, while the coldest months are June and July with an average of 79°F. The rainiest months in Porto Velho are March, February, January, and December, with each month seeing an average of 16 inches of rainfall.