Brazil is a year-round destination. Seasons in Brazil are the reverse of the northern hemisphere (winters in the US are summers in Brazil). Summers in Brazil are the rainy season and winters are the non-rainy season.
Only the southern region of Brazil experiences any major seasonal changes and can have cool weather. It is best to visit southern Brazil (Rio de Janeiro, São Paulo, Florianopolis) between September and March. Summer vacation begins in mid-December and lasts until February, during which time the beaches are packed and this can also be the rainiest time of the year in Rio.
If you are visiting Brazil’s northern region, the temperature will not vary much. In general, high season months include December, January, June, July and the beginning of August.