Petropolis’ Oceanic climate means that temperatures are mild throughout the year. You can visit any time and still enjoy much of the city’s charms. The climate is somewhat similar to Rio, though the higher elevation does make it cooler.
Winter (May to September): This isn’t an official winter as such, as the temperatures are still mild; the mercury fluctuates between 13 degrees Celsius at night to 23 degrees Celsius in the day time. July is the coolest month.
Summer (October to April): Temperatures are 17-27 degrees Celsius. February and March are the hottest months. The monsoon is between October and March; January and February are the rainiest months.
Ultimately the decision for best time to visit really comes down to whether you want to go when its lively, in July, or when its quiet. Weekends and Brazilian holidays sees people pour into town. If you’re only passing through, definitely don’t put Monday in your travel vacation itinerary planner, when almost everything fun is closed.