Sri Lanka’s climate can be described as tropical, and quite hot. Its position between 5 and 10 north latitude endows the country with the year-round warm weather, moderated by ocean winds and considerable moisture. The average temperature ranges from a low of 16 °C (60.8 °F) in Nuwara Eliya in the Central Highlands (where frost may occur for several days in the winter) to a high of 32 °C (89.6 °F) in Trincomalee on the northeast coast (where temperatures may reach 38 °C or 100.4 °F). The average yearly temperature for the country as a whole range from 28 to 30 °C (82.4 to 86.0 °F). Day and night temperatures may vary by 4 to 7 °C (7.2 to 12.6 °F). January is the coolest month, especially in the highlands, where overnight temperatures may fall to 5 °C (41 °F). May, the hottest period, precedes the summer monsoon rains.
The rainfall pattern is influenced by the monsoon winds of the Indian Ocean and Bay of Bengal and is marked by four seasons. The first is from mid-May to October, when winds originate in the southwest, bringing moisture from the Indian Ocean. When these winds encounter the slopes of the Central Highlands, they unload heavy rains on the mountain slopes and the southwestern sector of the island. Some of the windward slopes receive up to 2,500 mm (98.4 in) of rain per month, but the leeward slopes in the east and northeast receive little rain. The second season occurs in October and November, the intermonsoonal months. During this season, periodic squalls occur and sometimes tropical cyclones bring overcast skies and rains to the southwest, northeast, and eastern parts of the island. During the third season, December to March, monsoon winds come from the northeast, bringing moisture from the Bay of Bengal. The northeastern slopes of the mountains may be inundated with up to 1,250 mm (49.2 in) of rain during these months. Another intermonsoonal period occurs from March until mid-May, with light, variable winds and evening thundershowers.