Koh Samui weather in September 2025

Expect daytime maximum temperatures of 31°C in Koh Samui, Thailand in September and very high heat and humidity based on long-term weather averages. There are 6 hours of sunshine per day on average with 17 days with some rainfall and typically 141 mm of rainfall in the month.

  • 31°C maximum daytime temperature in September in Koh Samui31
    31°C max day temperature
  • 6 hours of sunshine per day
  • 17 days with some rainfall in September in Koh Samui17
    17 days with some rainfall
  • 24°C minimum night-time temperature in September in Koh Samui24
    24°C min night temperature
  • 12 hours of daylight per day in September in Koh Samui12
    12 hours of daylight per day
  • Very high heat & humidity in September in Koh SamuiVH
    Very High heat & humidity
  • 141 mm monthly rainfall in September in Koh Samui141
    141 mm of monthly rainfall
  • UV (maximum) index 11+ (Extreme) in September in Koh Samui11
    11+ (Extreme) UV index
  • 29°C sea temperature in September in Koh Samui29
    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)

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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.

JanFebMarAprMayJunJulAugSepOctNovDec

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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