The climate of Tonga is basically subtropical. Because the islands are in the southeast trade wind area, the climate is cooler from May to December, when the temperature seldom rises above 27° C (81° F ). The mean annual temperature is 23° C (73° F ), ranging from an average daily minimum of 10° C (50° F ) in winter to an average maximum of 32° C (90° F ) in summer. Average annual rainfall, most of which occurs from December to March during the hot season, is 160 cm (63 in) on Tongatapu, 257 cm (101 in) on Niuatoputapu, and 221 cm (87 in) on Vava'u. The mean relative humidity is 80%.