Sri Lanka has tropical climate with distinct wet and dry seasons, but it has two different monsoon seasons, as well as an ‘inter-monsoon’ season, from July – September, that affects different part of the island and at different times- If you’re prepared for unexpected bursts of rain, it’s still a good time of year to travel and to enjoy the beaches.
Temperatures remain high across the country at around 85°F average and the beaches are hot and dry. So regardless of when you choose to travel, you will enjoy some good weather depending on where you go. Generally, Sri Lanka is a round-the-year destination, you just have to know which side of the island to focus on in any given month and this is never more important than when planning your beach destination.
December to April is the best time to visit- like many South-East Asian destinations- as this is dry season and best for those looking for sun and sea. When you are enjoying the sea breeze on beaches, you'll hardly feel the humidity but once you leave the sand you'll certainly notice. Overall, the best time to see the whole country would be April and September and May to August is low season when the Yala Monsoon hits, nevertheless, it is still a favourable time to visit the North and East.