Brazil is so large that no single answer fits the whole country. In general, April–June and August–October offer the best balance of manageable weather, lower prices, and smaller crowds.
Rio de Janeiro and the Southeast: The hottest and most humid months are December–March, when temperatures regularly exceed 35°C and afternoon downpours are common. This is also Carnival season (February or March), so crowds and prices spike dramatically around that time. May–September is cooler and drier — and far more pleasant for sightseeing on foot.
The Northeast coast (Salvador, Recife, Fortaleza, Natal): The northeast has a warm tropical climate year-round, with average temperatures around 28–30°C. The rainy season runs roughly December–July, though showers come and go quickly. The driest and sunniest months are August–November, making that the most reliable time for beach holidays in Bahia and Pernambuco.
The Amazon: The Amazon is wet at any time of year. The main rainy season is December–May, when rivers flood and many roads become impassable. Counterintuitively, the high-water season (March–May) is popular with wildlife-watchers because you can canoe deep into the flooded forest; the low-water season (July–November) is better for hiking and seeing beaches on the riverbanks.
The Pantanal: Visit in the dry season (May–October) for serious wildlife watching — concentrations of animals around shrinking water sources make this one of the best wildlife destinations on earth. July and August are peak season. Avoid the wetlands January–April, when flooding makes much of the region inaccessible.
Key events: - Carnival — February or March (exact dates vary by year). Rio's Sambadrome parade and Salvador's street parties are the most famous, but every city celebrates. Book accommodation months ahead. - Festas Juninas — June. Enormous folk-festival celebrations across the Northeast, especially in Caruaru and Campina Grande. - New Year's Eve in Rio — December 31. Millions gather on Copacabana beach for fireworks. Hotels sell out a year in advance.