Kolkata has a tropical climate. The annual mean temperature is 26.8 °C (80 °F); monthly mean temperatures range from 19 °C to 30 °C (67 °F to 86 °F). Summers are hot and humid and maximum temperatures often exceed 40 °C (104 °F) during May and June. Winter tends to last for only about two and a half months, with seasonal lows dipping to the 12 °C – 14 °C between December and January. The highest recorded temperature is 43 °C (111 °F) and the lowest is 5 °C (41 °F). Often during early summer, dusty squalls followed by spells of thunderstorm and heavy rains lash the city, bringing relief from the humid heat. These thunderstorms are locally known as Kal baisakhi (Nor'westers).

The southeast monsoon rains lash the city between June and September and supplies the city with most of its annual rainfall of 1,582 mm. The highest rainfall occurs during the monsoon in August (306 mm). The city receives 2,528 hours of sunshine per annum, with the maximum sunlight occurring in March.[20] Pollution is a major concern in Kolkata, and the Suspended Particulate Matter (SPM) level is high when compared to other major cities of India,[21][22] leading to regular smog and haze.