Planning for the weather is a good way to make your trip to Porto Velho relaxing and enjoyable, especially when you’re splurging. 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.