Sri Lanka produces some good fun waves, offshore winds are super consistent during the monsoon season.The best surf season at the on the southwest (hikkaduwa etc) is from November to march and then on the east coast (arugam bay) from may to september. The coast from ArugamBay to Hikkaduwa is littered with long sand bottom point breaks and hidden reefs.
Sri Lanka is another one of those tropical destinations with distinct a dry and wet season. This gets slightly complicated as the change of seasons also brings a monsoon to each respective of the island. From May to October, it is the dry season on the east coast or the Arugam Bay side of Sri Lanka, with the west coast is being lashed by the monsoon. During the other time of the year, November to April, the opposite applies with the wet season coming to the east coast.
Generally the best time to travel to Sri Lanka is between November to March for the west coast, south coast and the hill country. For the east coast the best time is between April and September. This will keep you nice and dry and out of those monsoons. Coincidently this coincides with the surfing seasons as well.
Both the ocean and coastal lying regions of Sri Lanka have an average temperature of 27°C all year.