Koh Samui, Thailand
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Koh Samui

September beach and weather guide

Based on 5 years of historical ERA5 climate data

Photo by Marius Kriz on Unsplash

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September beach conditions — historical average

Excellent
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27.4°C Temp
30.2°C Sea temp
10.2 Rain days
8.8h Sunshine hrs
80.6% Humidity
100%

Reliable conditions

5 of 5 years were good

Year by year — mid September

2024 Excellent 27.4°C · 10 rainy days · 9.1h sun
2023 Good 28.1°C · 13 rainy days · 9.3h sun
2022 Excellent 27.2°C · 7 rainy days · 9.5h sun
2021 Good 26.8°C · 10 rainy days · 8.3h sun
2020 Good 27.5°C · 11 rainy days · 7.6h sun

Other months in Koh Samui

January February March July August September

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Each trip type is scored on what matters most for it — snow days for skiing, sea temp for beach, sunshine for sightseeing.

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About Koh Samui in September

Based on 5 years of ERA5 historical climate data, September in Koh Samui has historically been excellent for a beach holiday. Average temperatures of 27.4°C with sea temperatures around 30.2°C and 10.2 rainy days on average.

5 of the last 5 years had good beach conditions during this period. This data uses ERA5 reanalysis records — real historical measurements, not generalised averages.

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