Koh Samui Weather in September

September in Koh Samui typically sees daytime highs of 30°C (86°F) and nighttime lows of 27°C (81°F). Rainfall is also possible this month, so it's worth packing an umbrella.

Rainfall in Koh Samui in September

Historically, approximately 18 days this month are expected to have rain, averaging 156 mm (6.1 in). Wet weather is a regular and significant part of this month. Frequent days of rain combined with high totals means proper waterproofs are worth packing.

Temperature in Koh Samui in September

In September, Koh Samui gets high temperatures, with highs of 30°C (86°F). Nights cool to around 27°C (81°F). Conditions stay fairly consistent through the month, making it easier to plan what to wear. Nights are warm at 27°C (81°F), which can make sleeping uncomfortable. Keeping windows open or using a fan can help. A cold shower before bed is also a good way to cool down.

Sunshine in Koh Samui in September

You can expect a moderate amount of sunlight, with approximately 145 hours. This means a pleasant mix of sun and overcast.

Average water temperature in September

At 29°C (84°F), the water feels bath-warm. Fine for swimming, but those looking for a cooling swim may be a bit disappointed.

If you prefer dry days with pleasant temperatures, January and February typically offer the best circumstances. If you're seeking pleasant, dry and sunny weather somewhere else in the world, our weather planner can help you explore other options.

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For a detailed overview over the year and the best time to visit Thailand, check out our Koh Samui's climate page.

Koh Samui Temperature in September

Min Temperature 27°C (81°F)  

Max Temperature 30°C (86°F)  

Water Temperature 29°C (84°F)  

Chance of Rain 58%  

Precipitation 156 mm (6.1 in)  

Rainy days 18 days  

Humidity 79%  

Sunshine 145 hours  

Percentage Sunshine  

Daily Historical Temperatures

48-year average (1976-2025)

Based on our historical records, temperatures in Koh Samui typically stay consistent throughout September, with daily highs averaging around 30°C (86°F). Nights are warm, with lows around 26°C (79°F).

Average temperatures in September

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Daily Historical Precipitation

48-year average (1976-2025)

Average daily rainfall for each day of the month based on long-term records.

Average precipitation in September

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

‹ January February March April May June July August September October November December ›

Historical weather for Koh Samui in September

Browse day-by-day weather records for Koh Samui spanning 51 years. Select any month and year to see actual temperatures, rainfall, and conditions recorded on each day.

Historical weather Temperatures Precipitation

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‹ January February March April May June July August September October November December ›

Koh Samui historical weather extremes in September

Based on 39 years of weather observations in Koh Samui between 1986 and 2025, these are the recorded extremes.

• The warmest day in September was on September 5, 2025, with a maximum of 35°C (95°F).
• On September 23, 1992, Koh Samui saw its coldest September day with temperatures maxing out at 26°C (79°F).
• Koh Samui registered its coldest September night on September 25, 2012, with temperatures dropping to 20°C (68°F).

What to Wear in Koh Samui in September

Warm weather calls for comfortable, breathable clothing in September. Cotton t-shirts, shorts, light dresses, and sandals are perfect. You might still want a light layer for evenings or air-conditioned places (for example buses). Also bring a poncho, it will rain a lot! Waterproof everything you can. With water temperatures around 29°C (84°F), swimming conditions are excellent. Pack your swimsuit, goggles, and maybe some water shoes. Bring sunglasses since you'll have some sunny periods throughout the month

What To Do in Koh Samui in September

We rated the following activities from 1 (least suitable) to 10 (best) to do.

Swimming

7/10

Cycling

7/10

Walking

7/10

Camping

7/10

Outdoor sports

7/10

Select a Month

Check the conditions for any month of the year.

• January
• February
• March
• April

• May
• June
• July
• August

• September
• October
• November
• December

For a detailed overview over the year and the best time to visit Thailand, check out our Koh Samui's climate page.

More climate data for Koh Samui

Temperature Rainfall Sunshine Humidity Water Temp

See the full Koh Samui climate overview or explore weather in Thailand.