Rio de Janeiro sits on Brazil's southeast Atlantic coast, wrapped around Guanabara Bay and backed by forested mountains, just north of the Tropic of Capricorn at approximately 22.91°S, 43.17°W. It has a tropical climate (Köppen Aw) with a hot, humid, rainy summer and a warmer-than-mild, drier winter. Sea breezes off the Atlantic temper the heat along the famous beachfronts of Copacabana and Ipanema, while inland districts run hotter. Being in the Southern Hemisphere, its seasons are reversed relative to the Northern.

Summer, from December to March, is hot, muggy and the rainy season, with January and February the hottest months — average highs around 30–31°C but frequently much higher. Heat waves can push the thermometer to 35–40°C, and with humidity often near saturation the 'feels-like' temperature soars. Rain typically arrives as heavy afternoon showers and thunderstorms that can occasionally cause serious flooding and landslides on the steep hillsides, interspersed with plentiful sunshine.

Winter, from June to August, is dry and pleasantly warm rather than cold. Average highs stay around 25–26°C, and even the coolest nights rarely fall below the high teens; the temperature has essentially never dropped below about 10°C in the city. Sunny, comfortable days are the norm, though passing cold fronts can briefly bring cloud, rain and cooler, breezier conditions. This is the most comfortable season for sightseeing.

Rio receives around 1,100–1,250 mm of rain a year, heavily concentrated in the summer months from December to March, while winter is notably dry — June and July see the least rain. December is typically the wettest month. Summer downpours are often intense and convective, occasionally overwhelming the city's hillside neighbourhoods. Live rainfall, humidity, and pressure readings for the city are shown in the panels above.

A distinctive feature of Rio's weather is the arrival of Atlantic cold fronts from the southwest: when a southwesterly wind blows in, rain and cooler air usually follow, breaking the humid heat for a day or two. Humidity is a defining discomfort in the warm months, with dew points high enough to make muggy days blur into muggy nights, though the reliable sea breeze offers welcome relief along the coast.

To follow any single measurement in Rio de Janeiro more closely, use our live instruments: the online barometer for atmospheric pressure, the thermometer for temperature, the hygrometer for humidity, the anemometer for wind speed, the wind vane for wind direction, and the rain gauge for rainfall.