The south-west monsoon sets in during May. It brings wind and rain to the south and west coasts and turns the same airflow into an offshore on the east, so the points around Arugam Bay come alive over a few weeks while the south shuts down. Weligama and Midigama barely see a clean day in May, and they will not work again until November.
Understand the journey before you book, because it is the part people get wrong. Arugam Bay is six to eight hours by road from the airport, across the middle of the island rather than along the shore. It is a travel day: plan to arrive in daylight, with the car booked through the camp. Once you are there, the four points spread over about twelve kilometres, so a tuk-tuk or a scooter is part of the trip rather than an extra, and the camps run shuttles.
The waves are a different kind too. The south is a chain of reefs you walk between; the east is a run of long right-hand points you ride between. And the east is limited by swell size rather than by wind: at Whiskey Point, even at the height of the season, the wind spoils almost no days and the swell is simply too small on most. The number to watch on a forecast here is the height.
In May the season is still filling in, and that is the argument for coming. Pottuvil Point, the long right north of the bay, already gives five days out of seven, and hardly anybody is on it. The town is opening rather than open, prices and crowds are at their lowest of the east coast year, and the sea is 29°C. If you already surf, May is a quiet version of July. If you are learning, read the beginner note first: the gentle breaks need more swell than May usually sends.

