Ko Samui in Winter
In winter (December, January and February), Ko Samui sees average daytime highs around 27°C and overnight lows near 26°C, with 256 mm of rain over about 28 wet days across the season. It is the coldest season of the year and the driest season of the year.
Across winter, daytime highs hold fairly steady around 27°C. The sky is clear or mostly clear about 36% of the time across winter, and the air most often feels oppressive.
Winter is Ko Samui's best season of the year to visit on our travel score. Ko Samui has little temperature swing across the year, so its calendar seasons blur — the season framing matters less here than for a place with four distinct seasons. For the whole year in context, see Ko Samui's year-round climate.
- Avg daytime high
- 27°C
- coldest season of the year
- Avg overnight low
- 26°C
- Rainfall
- 256 mm
- 28 wet days
- Avg wind
- 18 km/h
- Travel score
- 6.6
- best season of the year
- Months
- Dec · Jan · Feb
Temperature in Ko Samui in Winter
Across winter, daytime highs hold fairly steady around 27°C.
A typical winter day in Ko Samui reaches about 27°C and drops to 26°C overnight. The warmest of the three months is February, the coolest January.
How winter really feels in Ko Samui
Once humidity and wind are folded in, winter brings about 0 days that feel above 32°C and 0 that feel at or below 0°C.
winter sits comfortably in between — no days that feel dangerously hot or drop to a hard freeze once humidity and wind are folded in.
Ko Samui weather by month
How the three winter months (December, January and February) compare with the rest of the year — the season's months are highlighted.
| Month | High / Low (°C) | Rainfall (mm) | Wet days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|
| Jan | 27° / 26° | 76 | 9.4 | 11.5 | 6.7 |
| Feb | 27° / 26° | 35 | 5.3 | 11.7 | 7.3 |
| Mar | 28° / 27° | 88 | 8.4 | 11.9 | 6.4 |
| Apr | 29° / 28° | 95 | 11.7 | 12.2 | 5.3 |
| May | 29° / 27° | 116 | 21.2 | 12.4 | 3.8 |
| Jun | 29° / 27° | 89 | 18.8 | 12.5 | 3.9 |
| Jul | 29° / 27° | 84 | 18.4 | 12.5 | 4.2 |
| Aug | 29° / 27° | 91 | 18 | 12.3 | 4.3 |
| Sep | 28° / 27° | 140 | 22.8 | 12.1 | 3.9 |
| Oct | 28° / 26° | 286 | 26 | 11.8 | 3.9 |
| Nov | 28° / 26° | 289 | 20.9 | 11.6 | 4.6 |
| Dec | 27° / 26° | 145 | 13.2 | 11.5 | 5.9 |
Cloud cover in Winter
The sky is clear or mostly clear about 36% of the time across winter.
Chance of precipitation in Winter
Ko Samui gets around 256 mm of rain over 28 wet days across winter. The line is the day-by-day chance of measurable precipitation.
Humidity in Winter
Most of winter feels oppressive — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Winter
Winds average 18 km/h across winter.
Sunrise & sunset in Winter
Daylight runs from about 11 h 30 min in early December to 11 h 48 min by late February. The lit band spans sunrise to sunset each day.
Solar energy in Winter
Average shortwave solar energy reaching the ground each day across winter, about 5.3 kWh/m².
Hazard calendar for Ko Samui
In winter, Ko Samui overlaps its cyclone and rainy season season. The full year is below, with each hazard's peak months called out.
Ko Samui sits in the North Indian Ocean cyclone zone; the season peaks May and October–November.
Ko Samui's rainy season runs September–December, when most of the year's rain falls.
Is winter a good time to visit Ko Samui?
Our two travel scores rate winter for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
winter is a reasonable time to visit Ko Samui for sightseeing. The water and warmth also suit a beach or pool day.
What to pack for Ko Samui in Winter
From winter's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In winter, Ko Samui sees daytime highs around 27°C and nights near 26°C. Pack light clothes. Worth having: rain gear and sun protection. About 28 days see rain.
Sea temperature near Ko Samui in Winter
The nearest coast averages about 28°C across winter — the other half of the beach question. The full-year curve and swim-comfort zones are below.
The sea offshore is warmest in May at about 30°C and coldest in January near 28°C.
The water stays above 20°C all year — warm enough for a swim any month.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Sea temperature (°C) | 28 | 28 | 29 | 30 | 30 | 30 | 30 | 29 | 29 | 29 | 29 | 28 |
| Comfort | Warm | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Tropical | Warm |
| Sea temperature (°C) | Comfort | |
|---|---|---|
| Jan | 28 | Warm |
| Feb | 28 | Tropical |
| Mar | 29 | Tropical |
| Apr | 30 | Tropical |
| May | 30 | Tropical |
| Jun | 30 | Tropical |
| Jul | 30 | Tropical |
| Aug | 29 | Tropical |
| Sep | 29 | Tropical |
| Oct | 29 | Tropical |
| Nov | 29 | Tropical |
| Dec | 28 | Warm |
UV index in Ko Samui in Winter
Clear-sky midday UV across winter averages around 11 (very high — sun protection essential). The full-year curve, shaded by WHO exposure level, is below.
Under clear skies, the midday UV index in Ko Samui peaks around August 22 at about 14 (extreme) — sunscreen, a hat and midday shade are essential. It bottoms out near December 18 at about 10 (very high).
The index reaches 3 or more — the level where the WHO recommends sun protection — every month of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 10 | 12 | 13 | 13 | 13 | 12 | 11 | 14 | 13 | 11 | 10 | 10 |
| Level | Very high | Extreme | Extreme | Extreme | Extreme | Extreme | Extreme | Extreme | Extreme | Extreme | Extreme | Very high |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 10 | Very high |
| Feb | 12 | Extreme |
| Mar | 13 | Extreme |
| Apr | 13 | Extreme |
| May | 13 | Extreme |
| Jun | 12 | Extreme |
| Jul | 11 | Extreme |
| Aug | 14 | Extreme |
| Sep | 13 | Extreme |
| Oct | 11 | Extreme |
| Nov | 10 | Extreme |
| Dec | 10 | Very high |
Air quality in Ko Samui in Winter
Average fine-particle pollution (PM2.5) through the year — so you can see where winter falls, not just the annual average.
Air quality in Ko Samui is worst in January — around 16 µg/m³ PM2.5 (moderate), and holds fairly steady the rest of the year.
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 16 | 15 | 13 | 14 | 13 | 14 | 15 | 12 | 12 | 11 | 10 | 12 |
| Level | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Moderate | Good | Good | Good | Good | Moderate |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 16 | Moderate |
| Feb | 15 | Moderate |
| Mar | 13 | Moderate |
| Apr | 14 | Moderate |
| May | 13 | Moderate |
| Jun | 14 | Moderate |
| Jul | 15 | Moderate |
| Aug | 12 | Good |
| Sep | 12 | Good |
| Oct | 11 | Good |
| Nov | 10 | Good |
| Dec | 12 | Moderate |
Where is Ko Samui?
Ko Samui sits at 9.5°N, 99.9°E, 8 m above sea level, in Thailand. The nearest listed city is Ko Pha-ngan, 27 km away.
Topography around Ko Samui
How much the land rises and falls, and what covers it, within 3, 16 and 80 km of Ko Samui.
Within 3 km, the terrain around Ko Samui has significant variations in elevation — a maximum elevation change of 476 m around an average of 56 m above sea level; within 16 km, large variations in elevation — a maximum elevation change of 629 m; within 80 km, very significant variations in elevation — a maximum elevation change of 1,358 m.
The land around Ko Samui is covered by trees (51%) and water (42%) within 3 km, water (72%) and trees (24%) within 16 km, and water (82%) within 80 km.
Thailand travel facts
- Travel advisory
- Level 1
- Exercise Normal Precautions
- Power plugs
- Type A / B / C
- 230 V · 50 Hz
- Prices
- ≈ 31% of US
- price level, 2025
- GDP per capita
- $8,057
- 2025
- Happiness
- 6.3 / 10
- World Happiness, 2025
- Homicide rate
- 4.8
- per 100k, 2011
- Road deaths
- 32.2
- per 100k/yr, 2019
- Income group
- Upper middle
- World Bank
- English
- Very low
- EF EPI 402
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for Ko Samui (9.5357°, 99.9357°, elevation 8 m), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google.