Gulf or Andaman islands: how to pick the right coast for your trip

The most consequential decision on a Thai beach trip is not which island to choose, but which coast. What many people do not know until after booking flights is that Thailand’s two coasts — the Andaman Sea to the west and the Gulf of Thailand to the east — have opposite seasons. It can be pouring rain on Phuket while Koh Samui has full sun, or the other way around. Choosing the wrong coast for your dates is the number one cause of frustrating beach trips in Thailand. This comparison clears the choice.

The map: where things are

The southern Thai peninsula has two coasts separated by a central mountain range. The Andaman Sea (west, facing Burma and the Nicobar Islands) holds the islands most famous in the tourist imagination: Phuket, Krabi, Phi Phi, Koh Lanta, Koh Lipe, plus the Similan and Surin groups. The Gulf of Thailand (east, facing Cambodia and Vietnam) holds the other great archipelago: Koh Samui, Koh Phangan, Koh Tao, Chumphon, and further east Koh Chang and Koh Kood.

Air access differs: Phuket has an international airport with European connections; Krabi, an international airport with fewer connections; Koh Samui, a private airport (Bangkok Airways) more expensive but direct; Koh Phangan and Koh Tao, no airport — you arrive by ferry from Samui or Chumphon; Koh Chang and Koh Kood also without airport — access is by car+ferry from Bangkok or Trat.

Seasons: the main criterion

Andaman. Dry season November to April. Rainy season May to October, with the strongest months in September and October (many services close). In rains, the sea is closed to small boats and many excursions are cancelled.

Gulf. Dry season January to September, with the best stretch between February and April. Rainy season October to December, with heavy storms in November. Koh Chang and Koh Kood, further east, also have rains from May to September.

If the trip is in December-January-February: both coasts work well. Andaman slightly superior for calmer sea.

If in March-April: both coasts work. Andaman at its peak; Gulf also.

If in May-June: Gulf clearly superior. Andaman entering rains.

If in July-August: Gulf superior. Andaman with rain risk but still viable in windows.

If in September-October: Gulf only. Andaman practically closed.

If in November: split. Gulf coming out of rains; Andaman starting season. Andaman preferable in the second fortnight.

Landscape: what each coast offers

Andaman. Vertical, rocky landscape, with limestone cliffs. Karst formations — rock islets emerging vertically from the water — are the iconic image. Phi Phi, Krabi (Railay), Phang Nga. Water generally transparent turquoise especially on small islands. Beaches usually small between cliffs. Greater density of snorkel and diving among reefs.

Gulf. More horizontal landscape, with jungle hills and long beaches. Koh Samui is large and mountainous but with extensive beaches. Koh Phangan has wild jungle sections to the north. Koh Chang has primary jungle. Darker blue water, longer beaches generally. Fewer spectacular rocky islets — with the exception of Ang Thong marine park, off Samui, which does have them.

For travellers seeking the image of rocky karst emerging from turquoise sea (the classic postcard image), Andaman. For those seeking long white-sand beaches and accessible jungle, Gulf.

Atmosphere and traveller profile

Andaman.

• Phuket: urbanised, all options from backpacker to luxury. Very saturated in high season. Patong, large-scale party centre, problematic. Quieter zones to the south (Kata, Karon, Nai Harn).
• Krabi (Railay and Ao Nang): more diverse, climbing, couples, families. Ao Nang is the gateway, Railay is more exclusive as it has no road access.
• Phi Phi: concentrated party island, very saturated in high season, spring break feel. Stunning natural setting but mass tourism.
• Koh Lanta: family-oriented, quiet, many long-stay European families. Less spectacular but very liveable.
• Koh Lipe: small, select, exclusive. Higher prices. Exceptional snorkel and diving.

Gulf.

• Koh Samui: the most cosmopolitan of the Gulf, mix of backpackers and luxury. Good beaches, complete infrastructure, Chaweng nightlife.
• Koh Phangan: two-faced. The south coast (Haad Rin) has the Full Moon Parties, large-scale party. The north coast (Thong Nai Pan, Bottle Beach) is wild jungle, yoga retreats, extreme tranquility.
• Koh Tao: world reference for budget diving and Open Water certifications. Backpacker and diver atmosphere. Small, with moderate nightlife.
• Koh Chang and Koh Kood: far less crowded, jungle, European families and weekend Thais. Koh Kood particularly quiet.

Prices and availability

Andaman is, in high season, notably more expensive than the Gulf, especially Phuket, Krabi and Phi Phi during December-January. Koh Lipe also has high prices due to its remote location.

The Gulf is, on average, more affordable throughout the year. Koh Tao and Koh Phangan are the most affordable islands; Samui has a wide range.

In low season (Andaman May-October, Gulf October-December), prices can be halved or thirds. Luxury hotels drop particularly in shoulder season.

Connections: how to combine islands

Andaman: ferry Phuket-Phi Phi (1h30m), Phi Phi-Krabi (1h30m), Krabi-Koh Lanta (2h), Koh Lanta-Koh Lipe (4h speed boat). All well connected by regular ferry in high season.

Gulf: ferry Donsak (peninsula)-Koh Samui (1h30m), Koh Samui-Koh Phangan (30m), Koh Phangan-Koh Tao (1h30m). Also well connected.

Combining the two coasts: from Phuket to Samui you can go by bus+ferry (8-9 hours) or domestic flight (Bangkok Airways 1h, 2,500-4,000 THB). From Krabi there is a direct flight to Samui in high season. It is not seamless: requires a full day of transport.

Recommendation by profile

First trip to Thailand, 10 days: choose a single coast. Andaman if going in dry season (Nov-April), Gulf if going May-Sept. Combine 2-3 islands within the same coast.

Short trip (1 week) purely beach: a single well-chosen island. For high season, Koh Lanta (quiet Andaman) or Thong Nai Pan (north Phangan). Avoid Phi Phi on first trip if seeking peace.

Long trip (3 weeks) with mainland: the coast will depend on dates. Can also include Koh Yao (between Phuket and Krabi, but quiet) or Koh Kood (east Gulf, very wild).

Diving: Koh Tao no question if budget matters. Similan and Surin (from Khao Lak, Andaman) if seeking world-class diving with the budget for it.

Party: Koh Phangan (Haad Rin) during Full Moon, or Phuket (Patong) any night.

Families with children: Koh Lanta, Koh Chang, Koh Samui (Bo Phut or Chaweng Noi), Koh Kood.

Luxury: Koh Yao Noi (quiet luxury), south Phuket (resorts), Koh Samui (Four Seasons, Ritz), Phi Phi Don (Laem Tong area).

The full Far Guides Thailand guide includes an island-by-island comparison table with access data, optimal season, typical profile, prices and specific recommendations for each type of traveller.