The north-east monsoon is properly established in December, and the south coast does what it will do until March: clean mornings, dependable waves, and a string of breaks from Ahangama to Hiriketiya that suits everybody from a first lesson in Weligama bay to the reefs at Midigama. In a week, count on five days out of seven at Plantations and three in Weligama bay. The east coast has been out of season since October.
The forecast is not what you plan around; the date is. The island fills from about the twentieth and stays full into the second week of January, and Weligama in particular is small. The first fortnight is the same surf with far fewer people on it, and it is the most useful thing to know about a December trip here. The second fortnight is the busiest stretch of the Sri Lankan year, and prices follow.
That makes the choice of village heavier in December than in any other month, because what varies between them is the crowd and not the wave. Weligama is the shortest transfer, two and a half to three hours from the airport, and the only sand, so it fills first and hardest. Midigama has four reefs over two kilometres, room on them even now, and is dark by nine. Ahangama has The Rock, a both-ways reef peak off Kabalana beach, and it has the evenings: rooftops, kitchens worth the walk, cafés that open early, and enough people arriving alone that nobody eats alone. Hiriketiya, at the eastern end, is the quiet option, lanes and early nights around a cove that keeps a wave when the open beaches close out.
The sea is 28°C, so a Christmas here is a rash vest and two sessions a day rather than a wetsuit and one. Book early whichever fortnight you choose, and if your dates can move, fly before the twentieth.

