Sri Lanka is a tropical island located in the Indian Ocean between six and ten degrees north of equator, accordingly the average temperature is quite high, fluctuating between 27° and 29° Celsius. However, winds brought inland by the sea have a regulating influence making coastal areas seem cooler due to sea breezes and lowering the temperatures in the central mountain regions that also seem colder due to the higher altitudes. Nuwara Eliya, for example frosts on some nights in December and January, so clothes that keep you warm are essential! Humidity levels are 90% at night and 70% during the day.
There are four rainy periods in Sri Lanka, the two monsoons that occur in the opposite halves of the country and the inter-monsoon showers. The South West monsoon arrives in May and goes on till September bringing up to 4000 mm of rain annually. The North East monsoon arrives in December and goes on till February brining around 1000 mm of rain annually. Connecting these monsoons, are the inter-monsoons, one occurring between October and November, the other between March and April. For a beach holiday on the South West coast, it is recommended to visit from November until April. For an East coast visit, during March and September.
When to go
Climatically, it is best to visit the West coast, the South Coast and the Hill country from December to March as it is the driest and often thought of as the best seasons for those areas. And April to September, it is the most promising time to visit the East coast and the Cultural Triangle which consist of the ancient cities. July or August is the time of the Kandy Esala Perahera, which is a 10 day festival honouring the sacred tooth relic of the Buddha, and also the time for the Kataragama festival in the South. In both towns accommodation just before, during and immediately after the festivals is very difficult to come by, and rates usually double or treble. Be sure to book rooms well in advance.