December to February
This is a popular period for the south and west coasts, cultural sites and classic island circuits. Expect warm coastal days, cooler evenings in the hills and higher demand around Christmas and New Year.
March and April
These inter-monsoon months can be hot and humid, with short afternoon showers. They are useful for flexible round trips, but early starts make cultural sites and walks much more comfortable.
May to September
The southwest monsoon brings more rain to Colombo, the southwest coast and parts of the hills. At the same time, the east coast around Trincomalee, Pasikudah and Arugam Bay can offer sunnier beach conditions.
October and November
The second inter-monsoon can bring showers across much of the island. Keep outdoor plans flexible, allow extra road time and use the changing light to enjoy lush landscapes and quieter attractions.
Weather is local
Check the forecast for each stop shortly before travel. A rainy morning in one region does not mean the entire island will have the same weather.
Official reference: Sri Lanka Tourism climate guide