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Chennai (formerly Madras) sits on the Coromandel Coast of southeastern India, on a flat coastal plain beside the Bay of Bengal at approximately 13.08°N, 80.27°E. It has a tropical wet-and-dry climate that is hot and humid for most of the year, and it is unusual among Indian cities in drawing most of its rain not from the summer southwest monsoon but from the retreating northeast monsoon later in the year. The sea keeps its temperature high and steady.
The hottest part of the year is the pre-monsoon period from April to June, with May and June the hottest — highs regularly around 37–40°C and, combined with the coastal humidity, a stifling 'feels-like' heat that locals call Agni Nakshatram, the 'fire star' period. Even the arrival of the summer southwest monsoon brings Chennai relatively little rain, since the city lies in its rain shadow, so early summer stays hot, muggy and largely dry.
Chennai has no real winter; its most pleasant, coolest weather comes in December and January, when highs ease to around 28–29°C and nights are comfortable, occasionally dropping to around 20°C. Even at its coolest the city stays warm, and humidity remains high. This mild, drier stretch from January to March is the best time to visit before the fierce heat returns.
Chennai receives around 1,400 mm of rain a year, the great majority delivered by the retreating northeast monsoon from October to December — November is by far the wettest month, and these rains can be intense enough to cause severe flooding, as in the catastrophic deluge of December 2015. The rest of the year is comparatively dry. Live rainfall, humidity, and pressure readings for the city are shown in the panels above.
Two things set Chennai's weather apart: its reliance on the northeast (retreating) monsoon rather than the southwest one that waters most of India, and its exposure to tropical cyclones. Storms spinning up in the Bay of Bengal most often threaten the Coromandel Coast between October and December, coinciding with the main rainy season and capable of bringing destructive wind, storm surge and flooding.
To follow any single measurement in Chennai 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.