The Coast
Contrary to 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.
The Highlands
The Andean Highlands have two typical seasons: wet and dry. From May to October rain is sporadic and sunshine fills the sky daily. It is often very pleasant in the Andes during this season and is the opportune time to undertake a trek or a trail in the region. It gets chilly at night regardless of the season owing to the high altitude so make sure you pack some warm clothes if traveling to this region. During the months of November through to April, rainfall is heavy and temperatures can plunge drastically after the sun sets. Nonetheless - traveling through the region during this period is still recommendable - it simply boils down to a question of being lucky with the weather.
The Jungle
The jungle is divided into the cloud forest (above 700m) and lowland jungle (below 700m). The cloud forest features a subtropical, balmy climate, with heavy rainfall between November and March, and sunshine from April to October. It is always cool at night.
The lowland jungle region is very tropical and has a warm and humid climate throughout the year with abundant rainfall between November and April. The average temperature at this time is 26°C, although it can reach 36°C. During this period it is advised that you bring a pair of Wellington boots as some of the jungle trails become small rivers.
The dry season runs from April through to October and daily temperatures can reach as high as 35°C. From time to time however, there are cold fronts that extend from the South Atlantic and drop temperatures to as much as 15°C during the day and 13°C at night. It is often thought that the dry season is the best season to visit the rain forest as the rivers are lower exposing the beaches, and the jungle routes are more accessible.