How warm is it in Koh Samui in September?

Daytime highs averaged 29.1 °C, night-time lows 27.5 °C. The highest value of the past 10 years was 30.4 °C (23 Sep 2024), the lowest 26.2 °C (15 Sep 2022).

How often does it rain in Koh Samui in September?

On average there were 26.2 rain days (at least 1 mm) with 206 mm of precipitation in total.

🇹🇭 Weather in Koh Samui in September

This is what the weather in Koh Samui (Thailand) was like in September in 2017–2026.

Key facts at a glance

Prevailing weather: Rain

Avg. daytime high

29.1 °C

28.7 °C – 29.6 °C

Avg. night-time low

27.5 °C

27.2 °C – 27.8 °C

Avg. rain days in period

26.2

87 % of days · ≥ 1.0 mm

Avg. precipitation in period

206 mm

118 mm – 329 mm

Avg. sunshine per day

n/a

Sunshine duration is not available from this data source.

Avg. sea temperature

–

Sea temperature unavailable for today (daily limit).

Extremes: Highest temperature 30.4 °C (23 Sep 2024) · Lowest temperature 26.2 °C (15 Sep 2022) · Avg. daily peak wind 20 km/h

Weather mix of all days

7Partly cloudy
30Cloudy
115Light rain
147Rain

Summary

On average 29.1 °C during the day and 27.5 °C at night.
On average 26.2 rain days (Rain day = at least 1.0 mm of precipitation) with 206 mm of precipitation in total.
Prevailing: Rain.
Warmest year: 2024 (avg. 29.6 °C), coolest: 2019 (avg. 28.7 °C).
Wettest year: 2020 (329 mm), driest: 2018 (118 mm).
Extremes: 30.4 °C on 23 Sep 2024 and 26.2 °C on 15 Sep 2022.

Overall values from all 10 years. How is this calculated?

Temperatures per year

Average over your travel period

Precipitation & rain days

Year by year

2026
Avg. max29.4°Avg. min27.7°
Rain days
29 Rain days
Precipitation
239 mm
Avg. sunshine per day
n/a
Sea temperature
–
Max 30.4 °C · Min 27.2 °C
2025
Avg. max29.0°Avg. min27.4°
Rain days
24 Rain days
Precipitation
165 mm
Avg. cloud cover
91 % cloudy
Sea temperature
–
Max 30.3 °C · Min 26.5 °C
2024
Avg. max29.6°Avg. min27.8°
Rain days
26 Rain days
Precipitation
144 mm
Avg. cloud cover
92 % cloudy
Sea temperature
–
Max 30.4 °C · Min 27.2 °C
2023
Avg. max29.2°Avg. min27.5°
Rain days
26 Rain days
Precipitation
222 mm
Avg. cloud cover
96 % cloudy
Sea temperature
–
Max 30.1 °C · Min 26.8 °C
2022
Avg. max29.2°Avg. min27.5°
Rain days
27 Rain days
Precipitation
233 mm
Avg. cloud cover
89 % cloudy
Sea temperature
–
Max 30.1 °C · Min 26.2 °C
2021
Avg. max28.9°Avg. min27.4°
Rain days
24 Rain days
Precipitation
157 mm
Avg. cloud cover
93 % cloudy
Sea temperature
–
Max 30.1 °C · Min 26.5 °C
2020
Avg. max29.0°Avg. min27.6°
Rain days
29 Rain days
Precipitation
329 mm
Avg. cloud cover
95 % cloudy
Sea temperature
–
Max 30.1 °C · Min 26.9 °C
2019
Avg. max28.7°Avg. min27.2°
Rain days
27 Rain days
Precipitation
220 mm
Avg. cloud cover
92 % cloudy
Sea temperature
–
Max 29.9 °C · Min 26.5 °C
2018
Avg. max28.8°Avg. min27.2°
Rain days
22 Rain days
Precipitation
118 mm
Avg. cloud cover
86 % cloudy
Sea temperature
–
Max 29.8 °C · Min 26.5 °C
2017
Avg. max29.2°Avg. min27.8°
Rain days
28 Rain days
Precipitation
238 mm
Avg. cloud cover
95 % cloudy
Sea temperature
–
Max 30.1 °C · Min 27.1 °C

Frequently asked questions

How warm is it in Koh Samui in September?: Daytime highs averaged 29.1 °C, night-time lows 27.5 °C. The highest value of the past 10 years was 30.4 °C (23 Sep 2024), the lowest 26.2 °C (15 Sep 2022).
How often does it rain in Koh Samui in September?: On average there were 26.2 rain days (at least 1 mm) with 206 mm of precipitation in total.

Check your exact travel dates

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Data sources

Weather data: Data obtained from the NASA Langley Research Center (LaRC) POWER Project funded through the NASA Earth Science/Applied Science Program
Reanalysis (weather model constrained by observations) on a coarse grid of about 50 km. Values represent a large area and can differ from local conditions, especially on islands, coasts and in mountains. No sunshine duration.
Reanalysis (weather model constrained by observations)
Reanalysis values represent a grid cell (approx. 25–50 km) and may differ from local measurements on coasts, islands and in mountains.
Sea temperature: MUR SST data were provided by JPL under support by NASA MEaSUREs program; accessed via NOAA CoastWatch ERDDAP
Daily multi-scale ultra-high resolution (≈ 1 km) analysis of satellite measurements (infrared, microwave) and in-situ data. Represents the foundation temperature below the daily warm surface layer. (Satellite and in-situ analysis)
Place search: Natural Earth (public domain) · GeoNames (CC BY 4.0) / OpenStreetMap (ODbL)