Rio has a tropical savanna climate (Aw) according to the Köppen climate classification and is often characterized by long periods of rain from December to March. The temperature occasionally reaches over 40°C (104°F) in inland areas of the city, and maximum temperatures above 30°C (86°F) occur on a monthly basis. In the main tourist areas (south side, where the beaches are located), the temperature is moderated by the cool sea-breezes from the Atlantic Ocean.

Rio de Janeiro Weather and Climate Data

Month	Average Sunlight (hours)	Temperature				Discomfort from heat and humidity	Relative humidity		Average Precipitation (mm)	Wet Days (+0.25 mm)
		Average		Record
		Min	Max	Min	Max		am	pm
Jan	7	23	29	16	39	High	82	70	125	13
Feb	7	23	29	17	37	High	84	71	122	11
March	7	22	28	18	36	Medium	87	74	130	12
April	6	21	27	16	34	Medium	87	73	107	10
May	6	19	25	13	35	Medium	87	70	79	10
June	6	18	24	11	32	Moderate	87	69	53	7
July	6	17	24	11	33	Moderate	86	68	41	7
Aug	7	18	24	12	34	Moderate	84	66	43	7
Sept	5	18	24	10	38	Moderate	84	72	66	11
Oct	5	19	25	14	39	Medium	83	72	79	13
Nov	6	20	26	15	38	Medium	82	72	104	13
Dec	6	22	28	13	39	Medium	82	72	137	14

Current Weather at
Galeão - Antônio Carlos Jobim International Airport
(better known as Galeão International Airport)
 

Along the coast, the breeze, blowing alternately onshore and offshore, modifies 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 average annual minimum temperature is 20°C (68°F), the average annual maximum temperature is 26°C (79°F), and the average annual temperature is 23°C (73.5°F). The average yearly precipitation is 1,086 mm. The minimum temperature recorded was 4.8°C (40°F) in July 1928; temperatures below 10°C (50°F) are very rare in the city. The absolute maximum reached 43.2°C (110°F) in January 1984. The temperature varies according to elevation, distance from the coast, and type of vegetation. Winter brings mild temperatures and less rain than the summer.

Some weather data sourced from BBC
Some text and data sourced and adapted from WikiPedia