Koh Samui Weather by Month & the Best Time to Visit
Quick answer: The best time to visit Koh Samui is January to April, when it is driest and sunniest. For boat trips and snorkelling, February to September usually has the calmest seas. The rainy season runs from October to December, with November the wettest month. Koh Samui sits on the Gulf of Thailand, so its weather pattern is different from Phuket and Krabi, and it stays drier through the middle of the year.
Koh Samui Weather by Month
| Month | Rain | What to expect |
|---|---|---|
| January | Low | Dry and sunny on land; seas can still be windy and choppy |
| February | Low | One of the best months: sunny, comfortable and calmer seas |
| March | Low | Sunny and getting hotter; great for boat trips |
| April | Low | Usually the hottest month; Songkran festival mid-month |
| May | Low to moderate | Hot, with occasional short showers |
| June | Low to moderate | Warm with calm seas; good for snorkelling |
| July | Low to moderate | Busy summer holiday season, mostly dry |
| August | Low to moderate | Mostly dry and sunny; popular with families |
| September | Moderate | Still a good month, with more frequent showers |
| October | High | Rainy season begins; heavy but often short downpours |
| November | Very high | The wettest month; Ang Thong Marine Park usually closes |
| December | High | Rain eases through the month; busy over Christmas and New Year |
Temperatures stay warm all year, usually between about 25°C and 33°C, with April the hottest month.
Dry Season in Koh Samui (January to April)
Best for: Beach days, sightseeing, outdoor activities
The dry season is the most popular time to visit Koh Samui. Days are warm and sunny, rainfall is low and the island is at its greenest after the rains. January can still bring windy days and choppy seas, but from February conditions are usually excellent both on land and on the water.
Explore our luxury longtail experiences to the southern islands for a relaxed and scenic way to discover Koh Samui’s surrounding waters.
Because this is a busy time of year, accommodation and tours can book up quickly.
Hot Season in Koh Samui (May to September)
Best for: Snorkelling, boat trips, island hopping
While much of Thailand has its rainy season in the middle of the year, Koh Samui stays mostly dry, with the occasional short shower followed by sunshine. The sea is usually calm, making this an excellent time for snorkelling, diving and private boat trips.
Ang Thong National Marine Park is an ideal day out at this time of year, with calm seas and good conditions for exploring the islands. For the best spots, see our guide to the best snorkelling around Koh Samui.
July and August are busy with summer holidays, so it is worth booking ahead.
Rainy Season in Koh Samui (October to December)
Best for: Fewer crowds, lush landscapes, better value
Koh Samui’s rainy season is shorter and later than in many other parts of Thailand. October to December brings the most rain, with November usually the wettest month. Rain often comes in heavy bursts rather than all day, and there are still plenty of sunny spells.
Some boat trips depend on the weather, and Ang Thong Marine Park usually closes for November. On land, the waterfalls are at their most impressive and the island feels noticeably quieter. Quad biking through the jungle and in-villa experiences such as a private chef or cooking class are great options in almost any weather.
The weather usually improves through December, and the island gets busy again over Christmas and New Year.
So, When Is the Best Time to Visit Koh Samui?
- For the best overall weather: January to April
- For snorkelling and boat trips: February to September
- For fewer crowds and better value: October to early December
Thanks to its tropical climate, Koh Samui is a year-round destination. With a little planning, you can enjoy the island’s beaches, marine life and experiences in every season.
Koh Samui Weather: FAQs
What is the best month to visit Koh Samui?
February and March are often the best, with dry, sunny weather and calm seas. January to April is the driest period overall.
What is the rainy season in Koh Samui?
October to December, with November usually the wettest month. Koh Samui’s rainy season is later than in Phuket and Krabi.
Is Koh Samui good to visit in the summer?
Yes. From May to September Koh Samui is mostly dry with calm seas, while much of western Thailand is in its rainy season.
Is it worth visiting Koh Samui in November?
It can be, if you are flexible. It is the wettest month and some boat trips, including Ang Thong Marine Park, may not run, but the island is quieter and better value.
When is the best time for boat trips and snorkelling in Koh Samui?
February to September usually has the calmest, clearest sea for boat trips and snorkelling.
How hot does Koh Samui get?
Temperatures are usually between about 25°C and 33°C all year, with April the hottest month.
Ready to plan your days? Browse all of our Koh Samui tours and experiences.
