Best Time to Visit Koh Samui: Month by Month

Here's the one thing to know about Koh Samui's weather: it runs opposite to the rest of Thailand. While Phuket, Bangkok and Pattaya are drying out, Samui is heading into its rains — and when the west coast is soaked in September, Samui is often sunny. Get this right and you'll always be on the correct coast.

The short answer

The most reliable time is December to April, with February and March the sunniest and driest, and the sea at its calmest and clearest. There's also a genuinely good mid-year window (June–September) when Samui stays relatively dry — handy when the Andaman islands are in full monsoon.

Why Samui is different

Samui is in the Gulf of Thailand, on the other side of the peninsula from Phuket, so a different monsoon governs it. Its wettest stretch is October to December — November above all — almost the mirror image of Phuket's September peak.

Practically, that makes the two islands a useful pair: if your dates fall in one's rainy season, the other is often dry. Choosing between them for a given month? Check both, or use the comparison tool for the cost side of the decision.

Dry season (December–April)

Samui at its best: warm, sunny days, gentle seas, and the island's full calendar. December and the new-year period are peak for crowds and prices; February and March give you the driest, clearest conditions with slightly thinner crowds. Ideal for beaches, snorkelling and boat trips to the Ang Thong marine park.

Mid-year window (May–September)

Often overlooked. Samui stays warm (30–35°C) and mostly dry through these months, with only short, occasional showers and lush green scenery. Prices are lower than the December peak and the island is calmer — a smart choice, especially if the west coast's monsoon has put you off Phuket.

Rainy / monsoon season (October–December)

The Gulf monsoon brings Samui's heaviest rain, strongest winds and roughest seas, peaking in November. Downpours are often short (20–60 minutes) rather than all-day, and the upside is the lowest prices and emptiest beaches of the year — but ferries can be disrupted and beach days are a gamble. Best for budget travellers who don't need guaranteed sun.

Festivals & events

Songkran (mid-April) — the water-festival new year. Samui Regatta (late May/early June) — sailing and beach parties. Loy Krathong (November) — floating lanterns. And the famous Full Moon Party on neighbouring Koh Phangan runs monthly, a short boat ride away.

Planning the rest of the trip? See the Koh Samui cost of living guide, or compare the island with its Andaman mirror in the Phuket best-time guide.