First of all, as a general rule, South America’s seasons are the opposite of North America’s seasons. So, when it’s summer in North America, Europe and Asia, it’s wintertime in South America. – See more at: http://news.southamerica.travel/best-times-to-travel-to-south-america.
During the Brazilian summer, from December-February, hotels, beaches, and tourist attractions are packed. During Carnival, Easter, Christmas, and New Year’s holidays, it’s also hard to find a room on the fly.
Make sure to book your Brazil vacation well in advance if you are planning on traveling to Brazil during those times. During the Brazilian winter, from June-August, Rio de Janeiro and other coastal towns still enjoy warm temperatures, with the occasional day of rain.
If you are traveling to the Amazon Rainforest or the Pantanal wetlands, choose a time during the dry season, between June and December, when there are less rains and less bugs to put a damper on your vacation. However, the rainy season, between January and May, is the best time for seeing wildlife.