September is Thailand's wettest and most unpredictable month.
That doesn't mean you shouldn't travel, but it requires careful planning.
If August is often surprisingly manageable, September is the point where you need to be more selective about where you go, what you plan, and how flexible your itinerary is.
Thailand Weather in September: Quick Overview
The weather in Thailand in September is hot and humid.
September sits at the peak of the rainy season, though it’s not the wettest everywhere, for example, the Gulf Coast is generally more stable.
Rain is frequent, but it rarely lasts all day. Most showers arrive in the afternoon or evening.
- Temperature: 25–32°C (77–90°F)
- Humidity: High, 83%
- Rain: ~300 mm, frequent showers, occasional heavy storms
- Sea Temperature: ~29°C (84°F) – Gulf coast better for beach time
- Sunshine Hours: 5-6
Is September a Good Time to Visit Thailand?
Yes. September is a good time to go if you:
- Prefer fewer crowds and a slower pace;
- Are flexible with daily plans;
- Focus on cities, culture, food, and nature rather than perfect beach days
It’s not ideal if your trip depends heavily on guaranteed sunshine or island hopping or you need fixed, outdoor-heavy schedules.
(For a broader comparison, see our guide on the best time to visit Thailand.)
Weather in Thailand in September by Region
Bangkok & Central Thailand in September: Heavy Showers, Quick Floods
Hot and humid, with rain more likely later in the day (~20 rainy days). Sightseeing is most comfortable in the morning, while afternoons are better for indoor plans.
After rain, Ayutthaya feels quieter, Kanchanaburi's waterfalls are at their strongest, and Khao Yai is lush and green. Heavy showers can cause brief flooding, but major tourist areas usually recover quickly.
In this month, heavy showers can cause brief flooding, but major tourist areas usually recover quickly. For city-specific tips, see our guide to Bangkok in September.
Northern Thailand in September: Greenest Landscapes, Frequent Rain
Slightly cooler than Bangkok, especially in the evenings, sometimes dropping to around 24°C. Rain is more frequent, with ~21 rainy days, but landscapes are at their greenest.
September works well for temples, food, and culture in Chiang Mai and Chiang Rai. Mountain views, such as Doi Inthanon or routes to elephant sanctuaries, may be partially obscured after rain. See Chiang Mai in September for planning tips.
Andaman Coast in September: Roughest Seas, Most Rain
Southern Thailand’s Andaman coast (Phuket, Krabi) often has rough seas and frequent rain (~20–22 rainy days). Boat trips and snorkeling are often cancelled, and some islands may close temporarily.
Gulf Islands in September: More Stable, Shorter Showers
The Gulf coast (Koh Samui, Koh Phangan, Koh Tao) is more stable (~13-15 rainy days). Rain still occurs, but it mostly comes as short afternoon showers, with sunny or partly cloudy skies in between. Activities usually resume quickly after a shower. Seas are calm, and water activities remain possible. If you want islands in September, this is the safer choice.
My experience: I traveled in Thailand in September 2024, visiting Bangkok, Chiang Mai, and Koh Samui. The forecast showed rain every day, but it rarely happened. In Bangkok, rain came briefly two or three times a day, usually lasting around 10 minutes. In Chiang Mai, we didn’t encounter any daytime rain over three days. In Koh Samui, there was only one short shower during four days.
I was visiting an elephant sanctuary in Chiang Mai in September, with clear skies and few visitorsThe Best Places to Visit in Thailand in September
September is not about chasing "perfect weather." It’s about choosing places that still work despite the rain.
If beaches are your priority, head to Koh Samui. Showers are common but often short, seas are calmer than on the Andaman coast, beach time is possible, and Koh Tao offers great diving conditions.
If you’re more into culture and food, Bangkok and Chiang Mai are solid choices. Rain rarely lasts all day, and as long as you stay flexible, temples, cafés, markets, and indoor attractions are easy to enjoy.
If nature is what you’re after, Kanchanaburi works well in September. Waterfalls are at their most powerful, the scenery is lush, and access is easier than in many national parks, where heavy rain can disrupt roads and trails.
Typical September Weather in Key Thai Destinations
| City | Low (°C / °F) | High (°C / °F) | Rainfall (mm) | Rainy days |
|---|---|---|---|---|
| Bangkok | 25 / 77 | 32 / 90 | ~280 | ~20 |
| Chiang Mai | 24 / 75 | 31 / 88 | ~250 | ~21 |
| Phuket | 25 / 77 | 31 / 88 | ~320 | ~21 |
| Krabi | 24 / 75 | 31 / 88 | ~310 | ~20 |
| Koh Samui | 26 / 79 | 31 / 88 | ~140 | ~18 |
Data Sources: Weather Spark & TMD historical averages
(September is Thailand's wettest month overall; figures are planning baselines—conditions vary yearly.)
Crowds and Travel Costs in September
September is one of the least crowded months in Thailand. Most sights, restaurants, and transport feel noticeably quieter, though crowd levels vary by region.
- Andaman coast (Phuket, Krabi): very few visitors, empty beaches, calm atmosphere
- Gulf coast (Koh Samui & nearby islands): busier than the west coast but far from peak-season crowds
- Bangkok and Chiang Mai: moderate crowds; popular attractions may have short waits, but overall experience remains relaxed
From a cost perspective, September offers some of the best value of the year, with prices typically 30–50% lower than peak season.
What to Wear in September
Keep it simple: lightweight, breathable clothes for the humid days, a light rain jacket or poncho, and waterproof footwear if you're planning to explore cities or nature after rain. Quick-dry fabrics are a lifesaver. And don't forget mosquito repellent—rain brings more bugs.
Travelling to Thailand in September?
If you're planning a trip and unsure how to balance destinations and timing, starting with a flexible Thailand itinerary makes September much easier to handle. You can also see our planning a trip to Thailand for more tips.
You could also check out our Thailand tours for inspiration.
- 10-Day Classic Thailand Tour: Bangkok, Chiang Mai, and Koh Samui
- 12-Day Thailand Wonders Tour: Bangkok, Kanchanaburi, Chiang Mai, and Krabi
Monthly Weather and Travel Information for Thailand
Learn about the weather in Thailand for 12 months and find out the best places to visit each month.
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