September · Thailand
Best time to visit Koh Samui in September Weather, crowds & prices
Weather in Koh Samui in September
Average temperature 25°C, 131 mm of rain, about 25 days with 6+ hours of sunshine and 80% humidity — based on the five most recent complete years of ERA5 data (2021–2025).
September score
7.6/10
Ranked #9 of 12 months
- Avg temp
- 25°C
- Rainfall
- 131 mm
- Humidity
- 80%
- Days with 6h+ sun
- 25
- Crowd Density
- Quiet / Uncrowded
- Average Expenses
- $ · Budget Friendly ($)
September in Koh Samui scores 7.6/10 for beach and coastal travel - ranked #9 of 12. Expect around 25°C, 131 mm of rain, and roughly 25 days with 6+ hours of sunshine this month.
Koh Samui's ring road links Chaweng's beach, Bophut's Fisherman's Village, and the Big Buddha on the north coast.
September holds up well in Koh Samui — 9th best month
September averages 25°C (77°F) — warm enough for beach and boat plans, still short of the heat that pushes sightseeing into early morning.
Monthly rainfall reaches 131 mm — wet for this destination — but about 25 days with 6+ hours of sunshine still break through, so keep one indoor fallback in the plan.
It scores 7.6/10 here, 9th of 12 months, against 9.3/10 in the destination's best month.
Pack light clothing, swimwear and real sun protection, a proper rain shell rather than an umbrella.
Plan for low-season pricing, with crowds are light for this destination.
Flexible dates? March scores 1.7 points higher here — enough to change the trip.
Frequently asked
- What is the weather like in Koh Samui in September?
- In September, Koh Samui averages 25°C, 131 mm of rain, and about 25 days with 6+ hours of sunshine. Its climate-comfort score is 7.6/10.
- Is September a good time to visit Koh Samui?
- September earns a 7.6/10 climate-comfort score. Use the year-round chart to weigh the weather against your budget and crowd preferences.
- How much does it rain in Koh Samui in September?
- Expect about 131 mm of rain in September. Average humidity is 80% and there are about 25 days with 6+ hours of sunshine.
Curated in Koh Samui
Tickets & experiences
Things to do in Koh Samui
Koh Samui, Thailand. Live activities and tours from GetYourGuide, matched to this destination.