The province of Sindh is situated in a subtropical region; it is hot in the summer and cold in winter. Temperatures frequently rise above 46 °C (115 °F) between May and August, and the minimum average temperature of 2 °C (36 °F) occurs during December and January. The annual rainfall averages about seven inches, falling mainly during July and August. The southwesterly monsoon wind begins to blow in mid-February and continues until the end of September, whereas the cool northerly wind blows during the winter months from October to January.
Sindh lies between the two monsoons — the southwest monsoon from the Indian Ocean and the northeast or retreating monsoon, deflected towards it by the Himalayan mountains — and escapes the influence of both. The average rainfall in Sindh is only 6–7 in (15–18 cm) per year. The region's scarcity of rainfall is compensated by the inundation of the Indus twice a year, caused by the spring and summer melting of Himalayan snow and by rainfall in the monsoon season. These natural patterns have recently changed somewhat with the construction of dams and barrages on the Indus River. Parts of southeastern Sindh receive rainfall of up to 36 in (91 cm) and some cities have received very heavy rainfall on occasion. In 2005, Hyderabad received 14.4 in (37 cm) in just 11 hours.
Sindh is divided into three climatic regions: Siro (the upper region, centred on Jacobabad), Wicholo (the middle region, centred on Hyderabad), and Lar (the lower region, centred on Karachi).
The thermal equator passes through upper Sindh, where the air is generally very dry. The highest temperature ever recorded in Sindh was 53.5 °C (128.3 °F), which was recorded in Mohenjo-daro on 26 May 2010. It was not only the hottest temperature ever recorded in Pakistan but also the hottest reliably measured temperature ever recorded in the continent of Asia and the fourth highest temperature ever recorded on earth. The previous record for Sindh and Pakistan, and for all of Asia, had been 52.8 °C (127.0 °F), reached on 12 June 1919.
In the winters, frost is common. Central Sindh's temperatures are generally lower than those of upper Sindh but higher than those of lower Sindh. Dry hot days and cool nights are typical during the summer. Central Sindh's maximum temperature typically reaches 43–44 °C (109–111 °F). Lower Sindh has a damper and humid maritime climate affected by the southwestern winds in summer and northeastern winds in winter, with lower rainfall than Central Sindh. Lower Sindh's maximum temperature reaches about 35–38 °C (95–100 °F). In the Kirthar range at 1,800 m (5,900 ft) and higher at Gorakh Hill and other peaks in Dadu District, temperatures near freezing have been recorded and brief snowfall is received in the winters.In gorakh temperatures in winter nights can sour down to -15.
The highest temperatures each year in Pakistan, typically rising to above 48 °C (118 °F), are usually recorded in Shaheed Benazeerabad District (previously called Nawabshah District) and Sibbi from May to August. Sometimes the temperature falls to 0 °C (32 °F); on rare occasions (once every 25 years or so) it has fallen to below −7 °C (19 °F) in December or January.