🔄 Updated 6 Jul 2026
Short answer: Koh Samui sits on the Gulf coast (along with Koh Phangan and Koh Tao), and it rains on a completely different schedule than the Andaman coast (Phuket, Krabi, Phi Phi) — Samui's heaviest rain falls October through December, right when Phuket is usually clear. January through September is mostly clear and sunny on Samui, great for beach days and diving — one real advantage over the Andaman coast, which gets its heaviest rain mid-year.
Month-by-month
| Period | Weather | Best for | Prices |
|---|---|---|---|
| Jan-Mar | Dry, clear skies | Beach days, diving | Moderate-high |
| Apr-Jun | Hot, little rain | Beach days | Moderate |
| Jul-Sep | Sunny, less rain than Andaman coast | When Phuket is rainy, Samui's often still good | Moderate |
| Oct-Dec | Heaviest rain, rough seas | Check the forecast before booking | Cheaper (low season) |
What most people get wrong
Thailand doesn't rain everywhere at once. The Andaman coast (Phuket, Krabi, Phi Phi) gets its heaviest rain May through October, while the Gulf coast (Samui, Koh Phangan, Koh Tao) gets its heaviest rain October through December. So if you're planning a Phuket trip and it looks rainy, Samui might be a better bet in some of those months (July-September especially) — or vice versa. If you're planning to visit Samui October through December, check the forecast close to your travel dates, since some years bring storms strong enough to suspend the ferry.
- Want the most reliable clear skies — come January to March, dry and cool
- Phuket's rainy but you still want a beach — try Samui July to September, often still clear
- On a budget — October to December is cheaper, but check the forecast before booking ferries or flights
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