Koh Samui has a climate that works quite differently from the rest of Thailand. Sitting in the Gulf of Thailand rather than facing the Andaman Sea, Samui follows its own weather cycles — when Phuket and Krabi are soaked by the southwest monsoon in summer, Samui is often sunny. Understanding this is key to choosing the right time for your trip.

Samui's Four Seasonal Periods

High Season: December to February. The best time for beach holidays. Rainfall is at its lowest — February averages just 58 mm across the whole month (around 5–6 rainy days). Air temperatures sit at 24–30 °C, the sea is calm and clear. Villas fill up fast and prices peak. December sees slightly more rain than January or February but remains very comfortable overall.

Spring Transition: March to May. Skies clear up and temperatures climb. May brings the first tropical downpours (up to 15 rainy days) but they are typically short and intense. The sea is warm and well-suited to swimming and snorkelling. Villa rates drop compared to the high season — a good choice if you want decent weather at better value.

Green Season: June to September. Expect tropical sunshine, vivid blue skies and short but heavy afternoon storms. Around 14–16 rainy days per month, but most showers pass quickly. Sea temperatures reach 31–32 °C. Accommodation prices are at their lowest. An excellent time for diving, surfing and active pursuits.

October to November: Off-Season. The rainiest months on the calendar. November averages nearly 490 mm of rainfall and around 20 rainy days — the peak of Samui's wet season. Swells appear, drawing surfers. Many smaller businesses close for the season. Not recommended for a standard beach holiday.

When Should You Visit?

For pure beach weather, choose December, January or February. For a balance of good weather and lower prices, March–April or June–August work well. Avoid November and early December if you are not prepared for extended rainy periods.

One important caveat: nature ignores the calendar. A warm sunny spell can arrive in December; an unexpected storm can hit in July. Always check a short-range forecast 5–7 days before your arrival for the most reliable picture.