Sri Lanka’s climate is largely driven by the Southwest and Northeast monsoons. The first Inter-Monsoon Season which is from March to April, the Southwest Monsoon Season which is from May to September; the second Inter Monsoon Season which is from October to November and the Northeast Monsoon Season which is from December to February.
Being between 5° and 10° north latitude, brings Sri Lanka a warm climate that includes moderate ocean winds and moisture. Mean temperature ranges from a low of 15.8°C in Nuwara Eliya in the Central Highlands, to a hotter temperature of 29°C in Trincomalee in the East. An average annual temperature is in the range of 26°C to 28°C. January being the coldest month and April and August being the warmest.
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.
The climate is probably at its best during the dry seasons. Traveling to the west, south and upland parts is best from December to March. It is best to travel to the eastern and east coast region between April and September.
Between December and March is the ideal tourist season while the months of July and August are festival season and it is recommended that bookings are done well in advance especially for accommodation.