Burundi in general has a tropical highland climate, with a considerable daily temperature range in many areas. Temperature also varies considerably from one region to another, chiefly as a result of differences in altitude. The central plateau enjoys pleasantly cool weather, with an average temperature of 20° C (68° F ). The area around Lake Tanganyika is warmer, averaging 23° C (73° F ); the highest mountain areas are cooler, averaging 16° C (60° F ). Bujumbura's average annual temperature is 23° C (73° F ). Rain is irregular, falling most heavily in the northwest. Dry seasons vary in length, and there are sometimes long periods of drought. However, four seasons can be distinguished: the long dry season (June–August), the short wet season (September–November), the short dry season (December–January), and the long wet season (February–May). Most of Burundi receives between 130 and 160 cm (51–63 in) of rainfall a year. The Ruzizi Plain and the northeast receive between 75 and 100 cm (30–40 in).