Shenzhen has a mild, subtropical maritime climate with plenty of rain and sunshine. Summer is as long as 6 months. The annual average temperature is 23.7℃, with the highest temperature reaching 36.6℃ and the lowest 1.4℃. The frost-free period can be as long as 355 days a year, with sunshine time being 1,975 hours a year; solar radiation 5,225 trillion joule per square meter; and relative humidity 72.3 percent. The rainy season lasts from May to September, with an annual average rainfall of 1,608.1 mm and occasional typhoons in summer and autumn.