There are over three thousand islands along the rugged coastline of Zhejiang. The largest, Zhoushan Island, is Mainland China's third largest island, after Hainan and Chongming. There are also many bays, of which Hangzhou Bay is the largest.  Zhejiang has a humid subtropical climate with four distinct seasons. Spring starts in March and is rainy with changeable weather. Summer, from June to September is long, hot, rainy, and humid. Fall is generally dry, warm and sunny. Winters are short but cold except in the far south. Average annual temperature is around 15 to 19 °C (59 to 66 °F), average January temperature is around 2 to 8 °C (36 to 46 °F) and average July temperature is around 27 to 30 °C (81 to 86 °F). Annual precipitation is about 1,000 to 1,900 mm (39 to 75 in). There is plenty of rainfall in early summer, and by late summer Zhejiang is directly threatened by typhoons forming in the Pacific.