Shanghai Weather. Shanghai weather is generally mild and moist, with four distinctive seasons - a pleasant warm spring, a hot rainy summer, a comfortable cool autumn, and an overcast cold winter. The weather of Shanghai in July and August is the hottest, with more than 10 days' high temperatures above 35 C (95 F). The coldest period is from late January to early February. The location at the estuary of the Yangtze River to the East China Sea makes the city so wet that it rains for about one third of the year.