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Thailand has two beach coasts, and they do not share a calendar. The Andaman coast on the west — Phuket, Krabi, Railay and Koh Lanta — is at its best from roughly November through April. The Gulf coast on the east — Koh Samui, with Koh Phangan and Koh Tao beside it — runs on a different cycle and is wettest from about October to December, which is exactly why it is the coast that works in the middle of the year. Pick the month first, then the party, then the airport. That order settles the question for almost every week in the sun.
Which Thai coast is dry in which month
Thailand's Andaman coast (Phuket, Krabi) is the reliable choice from November through April and takes the southwest monsoon from roughly June, peaking around September and October. Thailand's Gulf coast (Koh Samui) is the better bet from about June through September, then gets its own heaviest rain from roughly October to December. January to April is the window when both coasts are usually good at once.
| Month you fly | Better coast | What to know |
|---|---|---|
| November–December | Andaman (Phuket, Krabi) | The Andaman side is drying out into peak season; the Gulf is in its wettest stretch. |
| January–February | Either | Thailand's cool, dry peak nationally. Both coasts are usually good; prices and crowds are at their highest. |
| March–April | Either | The hot season. Both coasts generally dry; Songkran in mid-April fills the beach towns with water fights. |
| May | Gulf leans better | The tail of the hot season, before the Andaman rains settle in from about June. |
| June–August | Gulf (Koh Samui) | The Andaman monsoon has started; the Gulf is in its favorable stretch. |
| September | Gulf (Koh Samui) | Peak Andaman monsoon. The Gulf is still the better side. |
| October | Neither reliably | The Andaman monsoon is at its peak and the Gulf's heaviest rain is beginning. Go knowing that rain days are likely on either side. |
What "rainy" means on a Thai beach
A wet month on either coast rarely means a week of solid rain. More often it means heavy afternoon downpours, rougher water and red flags on the beaches, and boat trips that run less often or get cancelled. That last point matters more than the showers: the Andaman's signature days — the Phi Phi Islands, Phang Nga Bay, the Hong Islands — are all boat days, and a monsoon sea is what takes them off the table. On a calm-sea day, when to land at Maya Bay decides whether you catch it at its quietest or at its busiest.
Why the national "best months" can mislead you
Most "when to go to Thailand" advice is written for the whole country, and the whole country's dry season is the Andaman's dry season. If your dates fall between June and September, that advice points you at the wrong coast. The Gulf is the exception the general rule leaves out.
Which Thai coast suits a family with kids
For families, Phuket on the Andaman coast is the easiest Thai beach base in season: the island is road-connected to the mainland, so there is no boat transfer after a long-haul flight, and Kata and Karon pair good beaches with a calmer scene than Patong. On the Gulf coast, Koh Samui's Lamai and Choeng Mon do the same job in the months the Andaman is wet.
Andaman options for families
In Phuket, Kata and Karon are the family default — the same Andaman water as Patong without the Bangla Road nightlife, with plenty of restaurants in walking distance. Near Krabi, Koh Lanta is the quieter island base that suits families who want space over choice. Our guide to where to stay in Phuket breaks the island down beach by beach, and you can compare family hotels in Kata once the area is settled.
Railay is beautiful, and it is boat-only
Railay, the cliff-ringed peninsula near Krabi, has no road in: every arrival and every departure is a longtail transfer from Ao Nang or Krabi town, bags included. That is the magic for couples and climbers, and it is real work with small children and luggage. The Railay guide covers how the boats run; for a family it is usually better as a day trip than a base.
Gulf options for families
On Koh Samui, Lamai is more relaxed and family-friendly than Chaweng, and Choeng Mon is quiet. Chaweng is the liveliest beach on the island and suits families with older kids who want restaurants and water sports close by.
