The Surin Islands are one of the Andaman Sea’s finest snorkelling destinations — but like the neighbouring Similans, they aren’t open all year. Mu Ko Surin National Park closes for the monsoon, so when you come matters as much as where you stay. Here’s how the Surin season works and when to visit for the clearest water and calmest seas.

The park is only open about half the year

Mu Ko Surin National Park is officially open from roughly 15 October to 15 May, and closed for the rest of the year (mid-May to mid-October) during the southwest monsoon. The exact opening and closing dates are set by the park authority each season and can move by a week or two, so it’s worth confirming before you lock in dates. Outside the open months there are no day trips at all — the North Andaman is too rough and the park simply doesn’t run.

The best months: November to April

Within the open season, the sweet spot is November through April, when the Andaman is calm and the water is at its clearest. February, March and early April usually bring the best underwater visibility of the year — often more than 20 metres — which is peak season for snorkelling the Surin reefs. Early in the season (late October and November) the islands are quieter and a little cheaper, with visibility already very good and seas settling down after the monsoon.

Why Surin is worth the early start

The Surin Islands sit further north than the Similans, close to the Myanmar border, so the day begins before sunrise and the boat crossing is longer. The reward is some of the largest, healthiest shallow coral in Thailand, a strong chance of turtles, and the cultural dimension of the Moken sea-gypsy community that still lives on Ko Surin Tai. Because the reefs are so close to the surface, Surin is often rated the better snorkelling day of the two parks, even if the Similans win on beaches.

Khao Lak is the natural base for a Surin trip — the departure pier at Ban Nam Khem is the closest mainland launch point, giving you the shortest possible crossing and the earliest start. If you’re planning a trip, see our Surin Islands snorkelling day trip, and if you’re deciding between the two parks, the Similan Islands run on the same calendar and are the obvious alternative.