20-Year Climate Average
Koh Samui, Surat Thani, Thailand Weather in September
Normal High
80°F
Normal Low
74°F
Rainy Days
~26 of the month
Chance of Rain
88%
Humidity
79%
UV index
Not available
Daylight
12.2 hours
Peak wind
13 mph
Usually good for: beaches and outdoor dining.
Based on September climate records from 2006–2025 (Open-Meteo Historical Weather Archive). These are planning averages, not a forecast. Data: Open-Meteo.com, CC BY 4.0.
Current conditions
Forecast versus the climate baseline
82°F
It currently feels like 90°F with 71% humidity, a 72°F dew point and 3 mph wind. Climate averages describe the month; this live reading is what matters for plans today.
84° / 74° · 97% rain
80° / 71° · 100% rain
80° / 72° · 99% rain
Best Months to Visit Koh Samui, Surat Thani, Thailand
Ranked by historical rainy-day frequency — the driest months over the past 20 years.
Methodology
Monthly values use the 2001–2020 observation period. Temperature, precipitation, humidity or dew point, wind, UV and daylight are shown only when the selected source provides them; unavailable fields are never estimated or silently replaced. These are planning normals, not guarantees for a specific trip.
What is the weather like in Koh Samui, Surat Thani, Thailand in September?
The 20-year average high in Koh Samui, Surat Thani, Thailand in September is 80°F, with a low around 74°F and about 26 rainy days.