Plan your trip · Seasons
When to go to the Thai islands: two seas, two seasons
The Thai islands are a classic winter-sun escape, but they lie on two seas with two calendars. Pick your sea by the month.
Updated 2026-10-25
The Andaman Sea: November to April
Phuket, Krabi and Railay, Koh Phi Phi, Koh Lanta and the Koh Yao islands are at their best from November to April, the dry season of the north-east monsoon: clear skies and calm water for boat trips, diving and island hopping. From May to October the south-west monsoon brings rain and swell to the western shores, and some marine national parks close for the season.
The Gulf of Thailand: January to August
Koh Samui, Koh Phangan and Koh Tao are sheltered from the south-west monsoon, so they stay mostly dry through the Andaman’s wet months. Their own rainy season comes later: October to December are the wettest months, with heavy rain especially in November. From January the Gulf is calm and dry, and TAT describes January to May as Samui’s calm season.
The eastern seaboard: November to April
Koh Chang and Koh Samet, closest to Bangkok, follow the Andaman pattern: TAT notes calm seas at Koh Chang from November to April.
Christmas and New Year
Christmas and New Year fall in the Andaman’s peak dry season, and are the busiest weeks of the year in Phuket, Krabi and Phi Phi: book resorts and boats well ahead. In the Gulf, late December can still be wet.
Our advice: for winter sun from November to March, go west to the Andaman; from January to August, the Gulf is a fine choice too. Check the forecast and the national park notices before you book boat trips.