The temperatures in Koh Samui during September are extremely high, between 27°C and hot as 29°C, drinking water regularly is advisable.
You can expect rain for roughly half of the month of September in Koh Samui. We’re expecting roughly 8 to 15 days of rain, so your rubber boots and umbrella are going to see plenty of use this month if you’re keen on staying dry.
Our weather forecast can give you a great sense of what weather to expect in Koh Samui in September 2025.
If you’re planning to visit Koh Samui in the near future, we highly recommend that you review the 14 day weather forecast for Koh Samui before you arrive.
Temperatures
29° / 27°
Rainy Days
10
Snowy Days
0
Dry Days
20
Rainfall
188
mm
Sun Hours
10.9
Hrs
