Here is a quick weather chart to help you with planning your trip to Brazil at the initial stage:
In general terms Brazil has a tropical climate and is good to visit around the entire year. The climate varies from region to region though, as you can see in the chart above. As Brazil lies in the Southern Hemisphere, its seasons are the exact opposite of what Northern Hemisphere residents like us are used to. Their seasons run as follows:
Summer: mid December to mid March (usually the humidity is higher and it is very hot)
Autumn: mid March to mid June (it varies from region to region, but usually less rain)
Winter: mid June to mid September (very little rain apart from some areas in the North-East, chilly at night in the South)
Spring: mid September to mid December (same as Autumn)
Rio has hot and humid summers – circa 38°C and 98% humidity is very common. Rio winters are quite mild, with night temperatures dropping to 19°C, and daytime temperatures climbing to 30°C. Note that most houses and apartments are built to reduce the heat, and many restaurants and stores lack windows or doors, so it can actually feel chilly in the evening during winter time. São Paulo has a similar climate to Rio’s – hot in the summer and mild in winter. As São Paulo sits above a plateau at approximately 700m (2,300 ft.), it can sometimes get chilly, with daytime lows in June to September reaching 12°C. Also, in the mountain resort of Petrópolis and the historic towns of Ouro Preto and Tiradentes, it often gets cold enough to see your breath (5°C) in the fall and winter.
In the Northeast it is warm year-round with a pleasant ocean breeze. Temperatures vary between 25 and 35 °C. Short showers cool things down during winter months (June-July).
The park of Lençóis Maranhenses is good to visit after the rainy season, when the lagoons are full of water. This is the case from mid May till September.
In the Amazon it is hot and humid year-round, with temperatures hovering around 35-39 °C. The dry season (hot and sunny) lasts from June to December. As the rivers recedes, you’ll find that the beaches and islands reappear. The wet season typically runs from December to May. The humidity is higher in the rainy season, building up over the course of the day to produce a heavy downfall almost every afternoon. Even then, however, mornings and early afternoons can be clear and sunny. Although the best time to visit the Amazon is between July to October, when it is dry, there are some advantages seeing the Amazon at high water, when the forest is flooded and one can navigate between the branches of the trees in a canoe. There is also a chance to spot the jaguar climbing the trees at high water.
The Pantanal is very hot during the rainy season (December to March), with temperatures reaching 40 °C. The driest time of the year is May through to October. Things cool down considerably, although night time temperatures will seldom drop below 20°C. The best time to see animals, is during the dry season from April/ May to October.
In the South, things get colder in the winter (June to September) but it is a good time to visit the canyon because there won’t be so much fog and one can enjoy the views. In Florianópolis, many restaurants and even some hotels and pousadas shut down for the winter season. During winter there is a possibility of snow in Rio Grande do Sul and Santa Catarina. The dry season in the south runs from March to November, whereas December to February are wet and rainy.
Iguazu Falls are at theirs fullest in the rainy season, but usually at that time most of the trails are closed. This is the case from December to February, which is also a busy time with lots of crowds. For clear skies and hiking the trails is best to go during the dry season, so from June onwards. There is never a safe bet. Overall, Iguazu, like Rio and Paraty, is good to visit at anytime.