Travel deep dive
Andaman or Gulf: Choosing Your Thai Island Coast
Thailand's islands sit on two coasts that are further apart than the map suggests — not in kilometres but in weather, character and logistics. The single most useful fact in Thai trip-planning is that the two coasts run on roughly opposite rainy seasons, which means there is almost no month of the year without a good Thai island; there is only the wrong coast for that month. What follows walks through the seasonal flip, the character of each coast, the islands themselves, and the routing realities that decide more itineraries than any beach photo.
Updated 2026-08-16
The monsoon flip: why the calendar picks your coast
The Andaman coast — Phuket, Krabi, the Phi Phi Islands, Koh Lanta — takes its rain from the southwest monsoon, which broadly soaks the west side from late spring into autumn. The Gulf side — Koh Samui, Koh Phangan, Koh Tao — sits in the shelter of the peninsula for most of that period and takes its heaviest rain later in the year instead, in a shorter, sharper wet season toward the north-east monsoon. The result is the flip: when one coast is at its stormiest, the other is usually at or near its best.
In practice: the classic high season on the Andaman side runs through the cool, dry months around the turn of the year, when seas are calm enough for the small-boat trips the coast is famous for. The Gulf's sweet spot stretches long through the middle of the year — the months when the Andaman is wettest are often gloriously settled on Samui and its neighbours. Shoulder periods blur these lines, and a wet-season coast is not a write-off — mornings are often clear, prices gentler, beaches emptier — but rough seas cancel exactly the boat trips that justify the Andaman, so the flip deserves respect when islands are the point of the trip.
One planning consequence follows immediately: fixed dates should choose the coast, not the other way around. Travellers who pick the island first and the month second are the ones who meet the monsoon.
The Andaman: karst drama and small-boat country
The Andaman is the postcard coast — limestone towers rising sheer out of jade water, the scenery that made Phang Nga Bay and the Phi Phi Islands world-famous. It is at its heart small-boat country: the signature experiences are longtail and speedboat trips between karst islets, snorkelling bays reachable only by water, and the sea-cliff walls that have made Railay and Tonsai a rock-climbing destination with few equals in Asia.
Phuket is the coast's anchor and its own airport gateway — the largest, most developed island, with everything from family resorts to nightlife districts, and the practical base for reaching smaller neighbours. Krabi province, across the bay, trades Phuket's scale for scenery: Railay's cliffs, Ao Nang's beach-town bustle, and boat access to islands in every direction. Koh Lanta, further south, is the Andaman's slow island — long west-coast sunsets, a more local rhythm, and diving day-trips toward the far southern sites. The Phi Phi Islands remain the day-trip magnet; staying overnight buys the bays at dawn, before the boats arrive.
Divers rate the Andaman's far sites — the granite pinnacles and open-water reefs north-west of Phuket — among Southeast Asia's best, with the marine-park season itself a seasonal affair: the offshore parks close during the monsoon months and reopen for the calm season, so serious dive plans should check current park dates rather than assume year-round access.
The Gulf: the three-island circuit
The Gulf coast is really one archipelago with three personalities, strung close enough together that ferries make a natural circuit of them. Koh Samui is the comfortable one — an airport of its own, resort infrastructure across every budget, and quieter east- and south-coast corners for those who step away from the main strips. It is the Gulf's base camp and its easiest landing.
Koh Phangan carries the party reputation, and earns it once a month — but the Full Moon nights concentrate on one beach, and the rest of the island runs on an entirely different current: yoga and wellness retreats, jungle viewpoints, and north-coast bays that stay calm all month. Treating Phangan as only a party island is the most common mis-read on the coast.
Koh Tao, smallest of the three, is the training reef: one of the world's great places to learn to dive, with sheltered bays, short boat rides to sites, and a village culture built around dive schools. Snorkellers get almost as much value as divers — the shallow reefs around the island and its satellite islet are genuinely rewarding without a tank.
Logistics: two coasts, one decision
The coasts connect less easily than their proximity on the map implies. Each has its own approach — flights into Phuket or Krabi for the Andaman; flights to Samui or the mainland-rail-and-ferry route via Surat Thani for the Gulf — and crossing between them mid-trip means a land transfer across the peninsula plus fresh boat connections. It is entirely doable, and combination itineraries exist for longer trips, but on a one-to-two-week holiday the crossing costs the better part of a travel day each way.
The cleaner pattern for most trips: choose the coast the season favours, fly into its gateway, and spend the island days within that coast's own network — the Gulf's three-island ferry circuit, or the Andaman's hub-and-spoke boat trips from Phuket, Krabi or Lanta. Save the other coast for the other half of the year, and for the return trip Thailand tends to earn anyway.
Whichever coast wins, the practical footnotes are shared: island boats are weather-dependent and the last daily departures are earlier than airport habits expect; peak-season accommodation on the small islands genuinely sells out; and the mainland links — Surat Thani for the Gulf, Krabi town and Phuket for the Andaman — are comfortable overnight stops rather than places to race through.