Brazil - Climate and when to go to Brazil

Climate
Seasons are opposite to those in the Northern Hemisphere; winter is June-September and summer November-March. On average, the temperature during summer ranges from 25 to 40°C.
In Rio de Janeiro the average temperature range is 25 to 30°C in January and 17 to 25°C F in July.
It rains an average of 1m each year.
Most of the coastal plain is tropical but ocean winds have an effect on the high temperatures and humidity. They get 1-2m  of rain each year.
The south region of Brazil gets sharp seasonal variations. Winter temperatures are -6°C and frost is common.

When to go
Seasons are opposite to those in the Northern Hemisphere; winter is June-September and summer November-March. On average, the temperature during summer ranges from 25 to 40°C (75~100°F).
 
North of Rio de Janeiro
December through March
The weather is always warm and hot
 
Rio de Janeiro
Rio can get cool in July. For a few days, the maximum temperature can fall below 20°C.
The rainy season is January through March
 
São Paulo and the South
A bit chilly from June through August (with a bit more rain) and quite hot and a bit humid in the
Summer (January through March)
 
The Northeast/Salvador
Warm along the coast year round. When you go a bit more inland the differences between day and night are more accentuated. Hot during the day and cooler at night
 
Amazon
Amazon is tropical: Humid and up to 35°C warm, year around, more or less.