Koh Samui weather in September 2025

Expect 31°C daytime maximum temperatures in the shade with on average 6 hours of sunshine per day in Koh Samui in September. Check more long-term weather averages for Koh Samui in September before you book your next holiday to Thailand in 2025/2026.

31
31°C max day temperature
6
6 hours of sunshine per day
17
17 days with some rainfall
24
24°C min night temperature
12
12 hours of daylight per day
VH
Very High heat & humidity
141
141 mm of monthly rainfall
11
11+ (Extreme) UV index
29
29°C sea temperature

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The September weather guide for Thailand (Koh Samui) shows long term weather averages processed from data supplied by CRU (University of East Anglia), the Met Office & the Netherlands Meteorological Institute. Find out more about our data sources.

Metric (°C / mm) | Imperial (°F / inches)

More about Thailand

How hot is it in Koh Samui in September?

Daytime temperatures usually reach 31°C in Koh Samui in September with very high heat and humidity, falling to 24°C at night.

How sunny is it in Koh Samui in September?

There are normally 6 hours of bright sunshine each day in Koh Samui in September - that's 47% of daylight hours.

How warm is the sea around Koh Samui in September?

The average sea temperature around Koh Samui in September is 29°C.

Does it rain in Koh Samui in September?

There are usually 17 days with some rain in Koh Samui in September and the average monthly rainfall is 141mm.

Koh Samui September sunrise & sunset times

Browse the sunrise and sunset times for Koh Samui in September 2025. Select a month to view Koh Samui sunrise and sunset times for the next 12 months.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Date	Sunrise times	Sunset times
Monday, 1st September 2025	06:11	18:29
Monday, 15th September 2025	06:10	18:20
Tuesday, 30th September 2025	06:08	18:11

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Thailand - quick facts
Flight time^✝	15 hours
Time difference	UK +7 hours
Language(s)	Thai, Isan
Currency	Thai Baht
Electricity	A + B + C + O plug (230V)
Driving side	Left
Why visit?	Beaches Culture Nature Nightlife
Tourist info	Tourism Authority of Thailand