Ko Samui, nestled in the Gulf of Thailand, features a tropical monsoon climate with warm temperatures and high humidity year-round. The island experiences three main seasons: a dry season from December to February, a hot season from March to August, and a rainy monsoon season from late September to early December. Sunshine, lush landscapes, and warm seas make Ko Samui a beach lover’s paradise.
The best times to travel section shows how the months compare for a visit, so you can find the time of year that fits what you want to do.
Background colours of the months:
The colour shows the typical temperature: yellow (hot), green (mild) and blue (cold). How strong the colour is shows the travel season: full colour means high season, soft colour means shoulder season and soft-striped means off season.
Weather symbols:
Each month has one symbol showing what the weather is typically like, such as hot and sunny, freezing or a rainy or snowy season. Use them to quickly spot months that match the weather you want, or to avoid the ones that don't.
Crowdedness:
The people icon shows how busy the place usually is. The more people, the more crowded it gets.
Additional notes:
The grey info boxes point out special things worth knowing, like recurring weather issues or seasonal events.
Ko Samui’s tropical monsoon climate ensures consistently warm weather, with average daily highs ranging from 29°C in January to 32–33°C in April and May. Evenings remain balmy, rarely dipping below 24°C. The sea stays inviting year-round, averaging 28–30°C, perfect for swimming and water sports. Humidity is high, generally between 78–85%, but sea breezes provide some relief, especially along the coast.
The island’s dry season, from December to February, brings the most settled weather, with abundant sunshine, minimal rainfall, and calm seas – ideal for beach activities and exploring. The hot season (March–August) is marked by higher temperatures, intense sun, and occasional brief showers, especially in May and June, but days remain mostly sunny. The rainy season, from late September to early December, is characterised by frequent, often heavy downpours, particularly in October and November. Rain typically falls in short, intense bursts, followed by sunny intervals, and the landscape is at its greenest. Despite the rain, Ko Samui remains warm and inviting, with fewer crowds and lush scenery.
| Average climate data for Ko Samui, Thailand | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Month | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | Year |
| Average maximum temperature (°C) | 29 | 29 | 31 | 33 | 32 | 32 | 32 | 32 | 30 | 30 | 29 | 32 | 33 |
| Average minimum temperature (°C) | 24 | 25 | 25 | 26 | 26 | 26 | 25 | 25 | 25 | 24 | 24 | 24 | 24 |
| Average precipitation (mm) | 87 | 54 | 80 | 82 | 157 | 123 | 116 | 111 | 121 | 312 | 507 | 211 | 1,959 |
| Average rainfall days (days) | 11 | 5 | 4 | 8 | 16 | 15 | 15 | 15 | 16 | 20 | 20 | 15 | 160 |
| Average relative humidity (%) | 83 | 83 | 83 | 82 | 81 | 78 | 77 | 77 | 79 | 84 | 85 | 82 | 81 |
| Average water temperature (°C) | 28 | 28 | 29 | 30 | 30 | 30 | 30 | 29 | 29 | 29 | 29 | 28 | 29 |
| Average daily daylight hours (h) | 11 | 11 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 11 | 11 | 11 | 12 |
| Average daily sunshine hours (h) | 7 | 9 | 8 | 8 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 6 | 7 |
| Average UV index | 11 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 12 | 11 | 10 | 12 |
The best time to visit Ko Samui is from December to April, when temperatures are warm (29–31°C), rainfall is low, and sunshine is abundant. These months offer ideal conditions for swimming, snorkelling, and relaxing on the beach, with the calmest seas and the most reliable weather.
The least favourable time is from October to November, when Ko Samui experiences its heaviest rainfall, frequent thunderstorms, and rough seas. Outdoor activities and boat trips may be disrupted, but the island is quieter and the scenery is lush and green.
Ko Samui has a tropical monsoon climate with warm temperatures (29–33°C), high humidity, and plenty of sunshine year-round. The island has a dry season, a hot season, and a rainy monsoon period.
The best time to visit Ko Samui is from December to April, when the weather is dry, sunny, and ideal for beach activities, water sports, and exploring the island’s natural beauty.
Heavy rain is most common from late September to early December, especially in October and November. Showers are usually short but intense, with sunny intervals between downpours. The rest of the year sees only brief, occasional showers.
Sea temperatures in Ko Samui stay warm year-round, ranging from 28°C in winter to 30°C in summer. Swimming, snorkelling, and water sports are possible in any season.
Travel is possible year-round, but October and November are wettest, with frequent heavy showers and rough seas. Many activities continue, but some boat trips may be disrupted. The island is quieter and lush during this period.
Pack light, breathable clothing, sunblock, and a hat for sun protection. Bring a raincoat or umbrella for the rainy season, and waterproof bags for electronics. Sandals and swimwear are essentials for the beach.
Ko Samui is warm year-round, with nighttime lows rarely below 24°C, even in the coolest months. A light jacket may be useful for evenings during the dry season, but cold weather is extremely rare.
The warmest month, with the highest average maximum temperature, is April (32.6 °C). The month with the lowest average maximum temperature is January (29.1 °C). Overall, the average maximum temperature over the whole year is 30.9 °C.
The month with the highest average minimum temperature is April (26.1 °C). The coldest month, with the lowest average minimum temperature, is December (24 °C). Overall, the average minimum temperature over the whole year is 25 °C.
The month with the highest average water temperature is May (30.1 °C). The month with the lowest average water temperature is January (27.7 °C). Overall, the average water temperature over the whole year is 29.1 °C.
The wettest month, with the highest amount of precipitation, is November (507 mm). The driest month, with the least amount of precipitation, is February (53.9 mm). Over the whole year there are 1,959 mm of rainfall on average.
The month with the most days of rain is November (20 days). The month with the fewest days of rain is March (3.9 days). Over the whole year there are 159.6 days of rain on average.
The month with the highest average relative humidity is November (85.3 %). The month with the lowest average relative humidity is August (77 %). The overall average relative humidity over the whole year is 81.2 %.
The months with the longest days, so the most daylight, are May, June and July (Average daylight: 12.1 h). The months with the shortest days, so the least daylight, are January, November and December (Average daylight: 11.1 h). Over the whole year there are 11.6 h of daylight per day on average.
The month with the most sunshine per day is February (Average sunshine: 9 h). The month with the least sunshine per day is November (Average sunshine: 6 h). Over the whole year there are 6.7 h of sunlight per day on average.
The months with the highest average UV index are February, March, April, May, June, July, August, September and October (UV index: 12). The month with the lowest average UV index is December (UV index: 10). Over the whole year the average UV index is 11.7.
