Qingdao has a temperate, four-season, monsoon-influenced climate that lies in the transition between the humid subtropical and humid continental (Köppen Dwa) regimes. Winters range from cool to cold and windy, but are generally dry, with a January average of −0.2 °C (31.6 °F). Summer is generally hot and humid, but very hot days are rare, with an August average of 25.4 °C (77.7 °F). Due to its proximity to the coast and location on a peninsula, compared to most inland areas of China, its spring is delayed by one month, and the annual diurnal temperature variation is only 6.3 °C (11.3 °F); conversely, its fall is milder than inland areas in Shandong. The water temperature peaks at about 25 °C (77 °F) in late August. Thus, swimming is possible for two months on either side. The annual mean temperature is 12.96 °C (55.3 °F). Extremes since 1951 have ranged from −15.5 °C (4 °F) on 16 January 1958 to 38.9 °C (102 °F) on 15 July 2002.
During the summer months, the beaches of Qingdao are afflicted by massive algal blooms. The decomposing algae release large amounts of hydrogen sulfide gas, which produces an offensive “rotten egg” odor. Sea lettuce blooms, which are partially caused by seaweed farming in Jiangsu Province, led local officials to declare a “large-scale algae disaster” in 2013.