Sri Lanka's position between 5 and 10 north latitude endows the country with a warm climate, moderated by ocean winds and considerable moisture. The mean temperature ranges from a low of 15.8° C in Nuwara Eliya in the Central Highlands (where frost may occur for several days in the winter) to a high of 29° C in Trincomalee on the northeast coast (where temperatures may reach 37° C). The average yearly temperature for the country as a whole ranges from 26° C to 28° C. Day and night temperatures may vary by 4 to 7 . January is the coolest month, causing people, especially those in the highlands, to wear coats and sweaters. May, the hottest period, precedes the summer monsoon rains.

Humidity is typically higher in the southwest and mountainous areas and depends on the seasonal patterns of rainfall. At Colombo, for example, daytime humidity stays above 70 percent all year, rising to almost 90 percent during the monsoon season in June. Anuradhapura experiences a daytime low of 60 percent during the intermonsoonal month of March, but a high of 79 percent during the November and December rains. In the highlands, Kandy's daytime humidity usually ranges between 70 and 79 percen