Weather is probably a major factor when you plan your trip to Porto Velho, but bear 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 temperature of 28°C, while the coldest months are June and July, with an average of 26°C. The rainiest months in Porto Velho are March, February, January and December, with each month seeing an average of 409 mm of rainfall.