High season in Brazil lasts from the week before Christmas until Carnaval (which falls sometime in Feb or early Mar, depending on the year). Flights and accommodations are more expensive and more likely to be full during this period. Book well ahead of time for accommodations during New Year’s and Carnaval. This is the most fun time to travel — towns and resorts are bustling as many Brazilians take their summer vacations, the weather’s warm, and New Year’s and Carnaval are fabulously entertaining. If you want to spend New Year’s in Brazil, it’s best to arrive after Christmas. The 25th is really a family affair, and most restaurants and shops will be closed.
Other busy times of the year include Easter week and the months of July, when Brazilian schools and universities take their winter break, and August, when most Europeans and North Americans visit during the summer vacation. This is probably the worst time of year to travel; prices go up significantly, and except for in the north and parts of the Northeast, the weather can be iffy and downright chilly from Rio de Janeiro southward. One year in Rio, I suffered through 4 straight weeks of rain, and temperatures as low as 5 to 10 Celsius (40s-50s Fahrenheit) are not unheard of in the south. If you want to take advantage of the best deals and still have good weather, consider visiting Brazil in September or October. The spring weather means warm days in São Paulo, Iguaçu, and Rio, and tropical heat everywhere else; in the Amazon and the Pantanal, you’ll be there just before the wet season starts. As an added bonus, in Rio you’ll be able to attend some of the samba school rehearsals as they get ready for Carnaval (yes, they start 4 months early). Another good period for a visit is after Carnaval (early to mid-Mar, depending on the dates) through May, when you can take advantage of low-season prices, particularly in hotels, while still enjoying good weather.