Karachi has a hot desert climate dominated by a long “Summer Season” while moderated by oceanic influence from the Arabian Sea. The city has low annual average precipitation levels (approx. 174 mm (7 in) per annum), the bulk of which occurs during the July–August monsoon season. While the summers are hot and humid, cool sea breezes typically provide relief during hot summer months, though Karachi is prone to deadly heatwaves, though a text message-based early warning system is now in place which helped prevent any fatalities during an unusually strong heatwave in October 2017. The winter climate is dry and lasts between December and February. It is dry and pleasant in winter relative to the warm hot season that follows, which starts in March and lasts until monsoons arrive in June. Proximity to the sea maintains humidity levels at near-constant levels year-round. Thus, the climate is similar to a humid tropical climate except for low precipitation and occasional temperatures well over 100 F (38 C) due to dry continental influence.
The city’s highest monthly rainfall, 19 in (480 mm), occurred in July 1967. The city’s highest rainfall in 24 hours occurred on 7 August 1953, when about 278.1 millimetres (10.95 in) of rain lashed the city, resulting in major flooding.
Karachi’s highest recorded temperature is 47.8 °C (118.0 °F) which was recorded on 9 May 1938, and the lowest is 0 °C (32 °F) recorded on 21 January 1934.