Travelers to the Amazon should expect warm temperatures, humidity and at least some rain year-round.
Rainfall increases during the high-water season, which is December through May. During this period, banks overflow and the forest floods. While many animals retreat to high ground, this is a good time to watch for birds and see primates enjoying the plentiful fruit. Temperatures are a bit cooler but still warm.
The warmer and somewhat drier low-water season runs June through November, and this period is the best for spotting wildlife since animals can be seen on the exposed river banks.