Ko Samui in Fall
In fall (September, October and November), Ko Samui sees average daytime highs around 28°C and overnight lows near 26°C, with 714 mm of rain over about 70 wet days across the season. It is the 3rd-warmest season and the wettest season of the year.
Across fall, daytime highs hold fairly steady around 28°C. The sky is clear or mostly clear about 11% of the time across fall, and the air most often feels oppressive.
Fall is Ko Samui's 3rd-best season 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
- 28°C
- 3rd-warmest season
- Avg overnight low
- 26°C
- Rainfall
- 714 mm
- 70 wet days
- Avg wind
- 16 km/h
- Travel score
- 4.1
- 3rd-best season
- Months
- Sep · Oct · Nov
Temperature in Ko Samui in Fall
Across fall, daytime highs hold fairly steady around 28°C.
A typical fall day in Ko Samui reaches about 28°C and drops to 26°C overnight. The warmest of the three months is September, the coolest October.
How fall really feels in Ko Samui
Once humidity and wind are folded in, fall brings about 14 days that feel above 32°C and 0 that feel at or below 0°C.
The story in fall is heat — humidity pushes the afternoon "feels like" well above the raw temperature.
Ko Samui weather by month
How the three fall months (September, October and November) 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 Fall
The sky is clear or mostly clear about 11% of the time across fall.
Chance of precipitation in Fall
Ko Samui gets around 714 mm of rain over 70 wet days across fall. The line is the day-by-day chance of measurable precipitation.
Humidity in Fall
Most of fall feels oppressive — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Fall
Winds average 16 km/h across fall.
Sunrise & sunset in Fall
Daylight runs from about 12 h 12 min in early September to 11 h 30 min by late November. The lit band spans sunrise to sunset each day.
Solar energy in Fall
Average shortwave solar energy reaching the ground each day across fall, about 4.8 kWh/m².
Hazard calendar for Ko Samui
In fall, 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 fall a good time to visit Ko Samui?
Our two travel scores rate fall for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
fall is a reasonable time to visit Ko Samui for sightseeing.
What to pack for Ko Samui in Fall
From fall's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In fall, Ko Samui sees daytime highs around 28°C and nights near 26°C. Pack light clothes and rain gear. Worth having: sun protection. About 70 days see rain.
Sea temperature near Ko Samui in Fall
The nearest coast averages about 29°C across fall — 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 Fall
Clear-sky midday UV across fall averages around 12 (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 Fall
Average fine-particle pollution (PM2.5) through the year — so you can see where fall 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.