The short answer
When to go to Koh Samui
February and March are the most reliable months: Samui's driest month is February, and the sea is usually calm enough for boat trips. April is hotter but still manageable if you start early. May to September is warm and humid with moderate rain and fewer visitors, while October to December is the wettest part of the year, with November the peak, when boats and ferries can be disrupted. Older travellers should favour February to April and keep midday for the hotel pool or air-conditioning.
Month by month
Koh Samui weather by month
| Month | High | Low | Rain | Verdict | What to expect |
|---|---|---|---|---|---|
| January | 29°C | 24°C | 127 mm | Driest of the wet-season tail; some showers, calm seas returning | |
| February | 29°C | 25°C | 64 mm | Driest month; sunny, comfortable for beaches and sightseeing | |
| March | 30°C | 25°C | 116 mm | Hot and mostly bright; good sea for Ang Thong trips | |
| April | 32°C | 26°C | 83 mm | Hotter; plan sights early, rest midday | |
| May | 33°C | 26°C | 132 mm | Hot and humid with rising showers | |
| June | 33°C | 25°C | 134 mm | Warm, humid, showers; fewer visitors | |
| July | 32°C | 25°C | 117 mm | Humid with passing showers; less crowded | |
| August | 32°C | 25°C | 102 mm | Humid; showers but long dry spells | |
| September | 32°C | 25°C | 118 mm | Rain builds towards the wet peak | |
| October | 31°C | 24°C | 295 mm | Heavy rain begins; rough seas can cancel boat trips | |
| November | 30°C | 24°C | 445 mm | Wettest month; flooding and ferry disruption possible | |
| December | 29°C | 24°C | 263 mm | Rain easing; busy festive season, book early |
Temperatures and rainfall are long-term monthly averages. Check the forecast a few days before you travel.
Seasons at a glance
Koh Samui seasons for families and seniors
The easiest months: February and March
- February: Driest month; sunny, comfortable for beaches and sightseeing
- March: Hot and mostly bright; good sea for Ang Thong trips
Good, with small trade-offs: January and April
- January: Driest of the wet-season tail; some showers, calm seas returning
- April: Hotter; plan sights early, rest midday
Possible, with planning: May, June, July, August, September and December
- May: Hot and humid with rising showers
- June: Warm, humid, showers; fewer visitors
- July: Humid with passing showers; less crowded
- August: Humid; showers but long dry spells
- September: Rain builds towards the wet peak
- December: Rain easing; busy festive season, book early
Best avoided with parents or children: October and November
- October: Heavy rain begins; rough seas can cancel boat trips
- November: Wettest month; flooding and ferry disruption possible
Useful answers
Best time to visit Koh Samui: FAQs
What is the best month to visit Koh Samui?
February and March are the best months to visit Koh Samui, with January and April also good. February and March are the most reliable months: Samui's driest month is February, and the sea is usually calm enough for boat trips. April is hotter but still manageable if you start early. May to September is warm and humid with moderate rain and fewer visitors, while October to December is the wettest part of the year, with November the peak, when boats and ferries can be disrupted. Older travellers should favour February to April and keep midday for the hotel pool or air-conditioning.
Which months should I avoid in Koh Samui with elderly parents?
October and November are the months to avoid with older travellers. Heavy rain begins; rough seas can cancel boat trips Wettest month; flooding and ferry disruption possible
When does it rain most in Koh Samui?
November is the wettest month, with about 445 mm of rain on average. The hottest month is May, with average highs around 33°C.