Like most of Thailand, Bangkok has a tropical savanna climate in December to an average high of 35.4 °C (95.7 °F) in April. The rainy season begins with the arrival of the southwest monsoon around mid-May. September is the wettest month, with an average rainfall of 334.3 millimetres (13.16 in). The rainy season lasts until October, when the dry and cool northeast monsoon takes over until February. The hot season is generally dry, but also sees occasional summer storms. The surface magnitude of Bangkok’s urban heat island has been measured at 2.5 °C (4.5 °F) during the day and 8.0 °C (14 °F) at night. The highest recorded temperature of Bangkok metropolis was 40.1 °C (104.2 °F) in March 2013, and the lowest recorded temperature was 9.9 °C (49.8 °F) in January 1955.
The Climate Impact Group at NASA’s Goddard Institute for Space Studies projected severe weather impacts on Bangkok caused by climate change. It found that Bangkok in 1960 had 193 days at or above 32 °C. In 2018, Bangkok can expect 276 days at or above 32 °C. The group forecasts a rise by 2100 to, on average, 297 to 344 days at or above 32 °C.