Season by season
Cool & dry season
January sees the weather settle after the rains. From February to April skies are clear, winds light and seas flat, with underwater visibility often at its best — the most dependable time for courses and for trips to the outer pinnacles.
Hot season
May to September is hot and mostly dry, with occasional squalls and some wind on the west coast in June to August, when the east-coast bays come into their own. July and August are busy with summer travellers; book ferries and courses ahead.
Rainy season & sea conditions
From October the north-east monsoon builds, bringing heavy rain, strong winds and rough seas that peak in November. Ferries are disrupted, visibility falls and some businesses take a break. Conditions usually improve from mid-December.
Month by month
| Month | Avg high | Avg low | Rainfall | Crowds |
|---|---|---|---|---|
| January | 29°C | 24°C | 140 mm | Very busy |
| February | 30°C | 25°C | 60 mm | Very busy |
| March | 31°C | 25°C | 80 mm | Busy |
| April | 32°C | 26°C | 80 mm | Busy |
| May | 33°C | 26°C | 150 mm | Busy |
| June | 32°C | 26°C | 110 mm | Busy |
| July | 32°C | 25°C | 120 mm | Very busy |
| August | 32°C | 25°C | 110 mm | Very busy |
| September | 32°C | 25°C | 120 mm | Busy |
| October | 31°C | 24°C | 300 mm | Quiet |
| November | 30°C | 24°C | 500 mm | Quiet |
| December | 29°C | 24°C | 200 mm | Very busy |
Temperatures and rainfall are approximate long-term averages for the nearest weather station; individual years vary, and mountain areas are cooler than the figures shown.
Festivals & events
- March–May: The most likely months for whale-shark sightings, along with September–October.
- April: Songkran, Thai New Year, 13–15 April.
- June: World Oceans Day brings reef clean-ups and conservation events run by the dive community.
- July–August: Peak season for dive courses.
- November: Loy Krathong at full moon, weather permitting.
Our advice
For the calmest water and clearest dives, come between March and May. July to September is also good and coincides with the Andaman monsoon, making Koh Tao the obvious place to dive in Thailand then. Skip November. See also when to go to Thailand.
