Indo-Pacific
The seasonal pattern for Thailand — what each stretch of the year tends to bring, and what to plan around. Guidance, not a forecast.
Seasonal pattern, not a forecast — conditions vary; verify tides, weather and visibility locally before you go.
Thailand snorkels on two coasts with opposite seasons, so think in coasts rather than months. On the Andaman side the dry, calm, clear window is broadly November to April — which is also when the Similan and Surin national parks are open and the west-coast islands are at their best — while the southwest monsoon from roughly May to October brings wind, rain and swell, closes the parks and stops many operators running. On the Gulf side the calm window falls roughly in the other half of the year, broadly February to September, with the northeast monsoon months bringing wind, rain and reduced visibility to Koh Tao and the Gulf islands. The useful consequence is that outside the peak of either monsoon one coast is usually workable, and a flexible itinerary can follow the weather across the peninsula. Water stays warm enough for a rashguard every month, so temperature is rarely the planning question: wind, rain, visibility and national-park opening dates are. Verify the park season, the day's marine forecast and the local tide before you commit, and treat your skipper's call as final.
The key sites on Thailand’s destination page — the water this season is about.
📍 Andaman Sea, west of Khao Lak, Phang Nga province
📍 Andaman Sea, north of the Similans, near the Myanmar border
📍 Krabi province, Andaman Sea
📍 Gulf of Thailand, Surat Thani province
📍 Between Phuket and the mainland, Phang Nga province
Live conditions decide the day, not this page — check the local marine forecast and tide or water-level information for your dates before you go.
Opens tide-forecast.com in a new tab. We link out to it rather than quote conditions; it is not an affiliate link.
Thailand snorkels on two coasts that run on opposite clocks. The Andaman side — the Similan and Surin island groups, Phi Phi, and the Phang Nga coast — is the classic: granite boulders, coral gardens and big visibility in the dry, calm months, which is also when the national parks open. The Gulf side, and Koh Tao in particular, is the easy end of Thai snorkeling: shallow bays you wade into, warm water, and a calm season that falls in roughly the other half of the year. Thailand is not the place to expect untouched reef, and its busiest sites show real wear and real boat traffic — but the range is enormous, the logistics are simple, and the country has one honest trap worth naming up front: Phang Nga Bay and its James Bond island are a scenery-and-kayaking day, not a snorkeling destination.
Planning Thailand around a season?
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