Brazil is the largest country in South America and while 90 percent of the country lies within the tropical zone, over 60 percent of the population live in areas where altitude or sea winds moderate the temperature.
In general, most of Brazil can be visited comfortably throughout the year; it is only the South - which can be unbearably sticky in summer (Dec-Feb) and chilly in winter (June-Aug) - that has large seasonal changes. The rest of the country experiences brief tropical rains throughout the year which rarely affect travel plans.
The sheer size of Brazil is reflected in its climatic diversity; the Northern region is on the Equator and the Southern region is below the Tropic of Capricorn. One can basically define five distinct climatic regions throughout the country: equatorial, tropical, semi-arid, highland-tropical, and subtropical. Temperatures range from very hot and dry in the Northeast, humid and wet in the Amazon, to snow in some extreme cases in the Southwest interior. Below are more detailed descriptions of the climates one can expect to encounter while traveling in Brazil.
Amazon
Contrary to the popular belief that the Amazon is blistering hot, the average annual temperature is around 25°C (77°F) and rarely exceeds 32°C (90°F), with little variation throughout the year. Humidity can be high and heavy rains can occur depending on the season. This area is the rainiest and most humid in Brazil.
Pantanal
The Pantanal has two distinct seasons: the rainy season (Dec-March) and the dry season (July-Oct). Temperatures range from very hot and humid in summer, to 10°C (50°F) in winter (June-Aug).
Iguazu Falls
The climate is humid and subtropical with over 1700mm of annual rainfall and no dry season. Relative humidity is between 80-90%. The average temperature is a steady 19°C (66°F) to 21°C (70°F).
Bahia
Temperatures in Bahia vary according to whether you're on the coast or inland, but it is sunny and warm almost all year round. On the coast it rarely drops below 24°C (75°F), however, in inland areas such as Chapada Diamantina, evenings are chilly and warm clothes are required. There is a distinct rainy season from May to September. Occasionally cold fronts from the South follow the coast up to the Northeast and the weather can suddenly change and the temperature drop.
Rio de Janeiro
Temperatures in summer reach up to 40°C (104°F) with rains and humidity. In winter it rarely gets colder then 18°C (64°F). In areas close to the mountains, such as Paraty for example, temperatures are much cooler and there is less of a dry season. Cold fronts sometimes occur.