Thailand Monsoon Island Picker
Best coast and island by month with ferry cancel-risk.
What this solves
Thailand's two coasts have opposite monsoon seasons. The southwest monsoon (May–October) closes the Andaman (Phuket, Krabi) to small boats and creates rough seas. The northeast monsoon (October–February) lashes the Gulf (Koh Samui). Picking the wrong coast in monsoon season can mean cancelled ferries, dangerous swimming, and wasted days.
How to read results
Each island-month combination has a cancel-risk score, sea-condition rating, and best activity. January is peak on both coasts. April–September, the Gulf wins; November–March, the Andaman wins. October is the wettest month on both coasts — avoid if possible.
Limitations
- Monsoon dates are averages; weather shifts year to year.
- Some islands have micro-climates (e.g., Koh Tao is calmer than Koh Phangan in some months).
- Cancel-risk applies to ferries and speedboats; airlines operate year-round.
FAQ
When is Koh Samui best?
February to April — dry, calm seas. Avoid November and December when the northeast monsoon brings rain.
When is Phuket best?
November to March — dry season on the Andaman. Avoid May–October for beach holidays (rain, rough seas).
What about Koh Tao for diving?
Koh Tao has visibility year-round but best is March–May (calm Gulf) and September–October (warm water, though some storms). Avoid November (heavy Gulf rain).
Sources
- Thai Meteorological Department — published monsoon climatology.
- Tourism Authority of Thailand — monthly travel advisories.
- PADI dive center reports — typical Gulf/Andaman diving conditions.