Rio de Janeiro Weather

Climate
Rio has a tropical wet and dry or savanna type (Aw) that closely borders a tropical monsoon climate (Am) according to the Köppen climate classification, and is often characterized by long periods of heavy rain from December to March. In inland areas of the city, temperatures above 40 °C (104 °F) are common during the summer, though rarely for long periods, while maximum temperatures above 27 °C (81 °F) can occur on a monthly basis.

Along the coast, the breeze, blowing onshore and offshore, moderates the temperature. Because of its geographic situation, the city is often reached, especially during autumn and winter, by cold fronts advancing from Antarctica, causing frequent weather changes. It is mostly in summer that strong showers provoke catastrophic floods and landslides. The mountainous areas register greater rainfall since they constitute a barrier to the humid wind that comes from the Atlantic.

The city reputedly has had rare frosts in the past, but this has never been decisively confirmed. Some areas within Rio de Janeiro state occasionally have falls of snow grains and ice pellets (popularly called granizo, or "hail", although it is in fact melted and refrozen snow falling in the form of a ball—true hail, rather than just icy snow along showers, is much less common). These phenomena are definitely not rare or limited to a few regions, having already happened in the metropolitan area (including western suburbs of the city itself) several times in the 21st century. In other areas there is true snowfall more than once in each century (the last time this occurred in Rio de Janeiro state was in the mid-1980s), most commonly around the highest mountain in the state (for perhaps centuries thought to be the country's highest) and fifth highest in the country, Pico das Agulhas Negras, in the cities of Resende and Itatiaia (in lower latitudes than Rio de Janeiro, but much higher altitudes).

source: wikipedia