Best time to visit...
Amazon (the rainforest)
Pantanal (for bird and animal life watching)
Iguassu Falls (the world's largest waterfalls)
Rio de Janeiro (fun and beach life)
Salvador da Bahia (afro-american music, beach going)
Bahia, Fortaleza, Recife (hubs for top tropical beaches)
Sao Paulo (the business and industrial heart of Brazil)
Brazil's South (Florianopolis, Santa Catarina and other southern destinations)
Weather Big Picture
Brazil is a very wide country, with different climate zones. And though there are many all year-round travel destinations, it's important to have into account some basic climate and weather factors.
The brazilian weather is mostly caractherized by a two-season pattern: a rainy season (often in the "summer") and a non-rainy season. And it's the rain - and the humidity, in some cases - that you should consider as the key factor, when planning your holidays.
Though high temperatures combined with high (or low) humidity can be an issue in some months and places (Brasilia or Belem and the Northern Amazon for instance), that's rather an exception.
The cold is not an issue either. It makes cold in the south of Brazil, in the winter months (where there is an atypical four season climate); low temperatures may also drop significantly during the nighttime (though not to freezing levels) in some inland locations (Pantanal, during the lll, for instance). But that's once more exceptions to the big picture.
For details on local weather conditions and the best time to visit dozens of Brazilian travel destinations, see: Best time to visit...
Sea water temperatures
Most coastal tourist destinations have tropical seawater temperatures - above 80ºF (27ºC) all throughout the year.
The time of the year only becomes relevant in the Rio area, and south of Rio the Janeiro. Here you should consider the time of the year.
The Amazon basin climate is humid and rainy - and by rainy we mean that it rains significantly even in the driest months. There are typical afternoon rainstorms during most of the year (fortunately for visitors, they do not last long, at least during the driest months).
Average temperatures are high (80ºF/27ºC to 90ºF/32ºC all throughout the year) with occasional cold spells in the May-September time, during the nighttime. The problem - from a thermal comfort perspective - is the combination of high temperatures with humidity, and the rain (in the rainy season).
The rainy season begins in mid-October in the southern region of the Brazilian Amazon and in December in Manaus, and it lasts until March (in the south), mid-May (in Manaus) or June (Belem). Note: Manaus - at the center of Amazon basin - and Belem - at the mouth of the Amazon river - are the major travel hubs in the region.
Remember: when planning your visit to the Amazon, try to avoid the rainy season. The driest months (which also have the lowest humidity levels) are a much better choice.
Though December and January are a very popular time, these months aren't the best time to visit the Amazon. Consider, if possible, a driest time, which will also be better to observe aquatic life in lakes, or birds, or for fishing and swimming.
Choosing the best time to visit Rio de Janeiro depends a lot on your focus.
Rio's climate is hot and subtropical in the November to February time - the high season, when beach activity, fun and entertainment (beach and sea sport events, Carnival rehearsals, Brazilian and Argentinean holidays) are at their highest.
This time is also the rainiest, but typical rainstorms do not last long; beach going (and holidays) is not significantly impacted by it.
But if you are not looking for fun and are not attracted by the Carnival period, there are better times to visit Rio. April and May - for instance - are great for travelling. Average air temperatures are a little cooler, but still excellent for beach activity and to travel.
For details and data on weather and regional events, see:
Visiting Rio de Janeiro in August 2016
Best time to visit Rio de Janeiro
Best time to visit Buzios, Cabo Frio
Best time to visit Angra dos Reis
Best time to visit Paraty, Petropolis.
What's the best time to go to Salvador da Bahia, Fortaleza, Recife or other beach resorts near these towns (Praia do Forte, Porto Galinhas, Natal, etc.).
From a weather perspective, the dry season (with lower levels of precipitation and humidity) is the best time to visit Bahia, Fortaleza or Recife. During the dry season (locally called the "winter") the temperatures rarely dip below 25ºC (77ºF) or rise beyond 32º or 33ºC (90ºF). The 'winter' temperatures are just a couple of degrees below the 'summer' temperatures.
On the other hand, seawater temperatures remain high all throughout the year.
Note that the Brazilian high season - the one with more people, more fun, more festivals, more music - goes from mid-December to March, which are typically dry months in the Salvador region (Bahia); but that's not exactly what happens in Recife (Pernambuco) and Fortaleza (Ceará). In these last regions the months of February or March are typically rainy. In other words: they aren't the best time for thermal comfort.
Sao Paulo's summer (December - March) can be very humid and rainy, while its winter temperatures (June - September) are typically moderate (55-75º F/13ºC-24ºC). They rarely hit freezing, though they can drop to low levels.
The driest months (June and July) have mild temperatures (above 55º F/13ºC) and are an excellent time to visit the city. But it depends also on your focus or on issues like local events.
For more details, and to know the best months to visit the region and coastal beaches, see:
The south of Brazil hasn't a tropical or subtropical climate; the climate is temperate, with the typical four seasons and cold temperatures during the local winter months.
The best time to visit this part of Brazil - and interesting travel destinations such as Curitiba, Florianópolis, Porto Alegre - and to experience local entertainment, fun and festivals is the summer months (December-March) or the months leading up to summer or immediately after the summer.
Pantanal looks like an African savannahin the peak of the summer, or an immense lake during a large part of the year. But the Pantanal is also a paradise for bird and animal watching - as long as you go at the right time.
The best time to visit the Pantanal is the dry months, that is, April to September, or a little later.
See for details:
Best time to visit the Pantanal
Compared to Iguassu, the Niagara Falls are a leaky faucet - to use the words attributed to Eleanor Roosevelt. The Iguassu Falls are, undoubtedly, one of the greatest natural wonders of our world.
But which is the best time to go? The falls aren't at their peak during the dry months, some tracks may close during rainy days, and the place is very crowded during some periods - especially in January and February, when most Brazilians and Argentineans are on holidays.
See for more details, and the pros and cons of the different months: Best time to visit the Iguassu Falls.