Shenzhen has a mild, subtropical maritime climate with plenty of rain and sunshine. The annual average temperature is 23.7 degrees of centigrade, with the highest temperature reaching 36.6 degrees of centigrade and the lowest 1.4 degrees of centigrade. 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.