What is the best time to dive Koh Tao? It’s the first question almost every diver asks before booking their flight. The short answer: whenever you can come. The water is warm year-round, boats go out 365 days a year, and there’s no bad season — just different seasons. Some months give you 30-metre visibility. Others bring whale sharks. This guide tells you which is which.
Water temperature
Max visibility
Days per year
Whale shark peak
Diving Koh Tao year-round: why is it possible?
Koh Tao has one advantage most dive destinations don’t: no off-season. Water temperature stays between 28°C and 31°C all year — a 3mm wetsuit is enough, and plenty of divers skip it altogether. The Gulf of Thailand is naturally sheltered, which keeps extreme weather mostly at bay.
Even during the rainy season (October to December), we go out to sea almost every day. When the west side is choppy, we switch to the east coast — Hin Wong Pinnacle, Tanote Bay — naturally protected from the prevailing winds. Cancellations are rare.
Best time to dive Koh Tao — month by month guide
Here are the average conditions you can expect depending on when you visit:
| Month | Conditions | Visibility | Water | Whale sharks |
|---|---|---|---|---|
| January | ⭐⭐⭐⭐⭐ | 20–30 m | 28°C | 🦈 Possible |
| February | ⭐⭐⭐⭐⭐ | 20–30 m | 28°C | 🦈 Possible |
| March | ⭐⭐⭐⭐⭐ | 20–30 m | 29°C | 🦈🦈 Peak |
| April | ⭐⭐⭐⭐⭐ | 20–30 m | 30°C | 🦈🦈 Peak |
| May | ⭐⭐⭐⭐⭐ | 15–25 m | 31°C | 🦈🦈 Peak |
| June | ⭐⭐⭐⭐ | 15–20 m | 30°C | 🦈 Possible |
| July | ⭐⭐⭐⭐ | 15–20 m | 30°C | 🦈 Possible |
| August | ⭐⭐⭐⭐ | 15–20 m | 30°C | 🦈 Possible |
| September | ⭐⭐⭐ | 10–20 m | 29°C | 🦈 Possible |
| October | ⭐⭐⭐⭐ | 15–25 m | 29°C | 🦈🦈 Peak |
| November | ⭐⭐⭐ | 10–20 m | 28°C | 🦈🦈 Peak |
| December | ⭐⭐⭐ | 10–15 m | 28°C | 🦈 Possible |
The three diving seasons in Koh Tao
🌞 January to May — The best time to dive Koh Tao
Visibility up to 30 metres, flat seas, water at 28–31°C. This is peak season, and it earns it. Whale sharks show up most here — at Sail Rock and Chumphon Pinnacle especially. We had two appear on the same dive in April, which is the kind of thing you don’t really forget. Not guaranteed, but your odds are as good as they get. Downside: it’s the busiest period on the island. Book ahead.
☁️ June to August — Decent conditions, fewer people
Visibility drops slightly to 15–20 metres, but the water is still 30°C and the sites are quieter. Whale sharks still pass through, just less often. It’s an honest window — not the most spectacular, but you won’t be sharing the Sail Rock chimney with three other boats. Good time for an Open Water course or Divemaster training.
🌧️ September to December — Rainy season
September is the most unpredictable month. Rain, some wind, occasionally reduced visibility. Still diveable — we still go out. From October things settle, and whale sharks come back for a second peak in October–November. December trends back toward good. Fewer tourists, lower accommodation prices, and the east coast sites hold up nicely throughout.
Want a whale shark? Go March–May or October–November. Want good conditions without the crowds? June–August. Have fixed dates and no choice? Come anyway — we dive year-round and we’ve rarely been disappointed.
When to see whale sharks in Koh Tao?
The whale shark is the world’s largest fish — and honestly, one of the few underwater encounters that genuinely stops you in your tracks. At Koh Tao, sightings happen year-round, but two windows concentrate most of the reports:
Frequently asked questions about the best time to dive Koh Tao
Tell us your dates and we’ll tell you what’s likely. And if you’re lucky, a whale shark will decide to show up too.
