September is the wettest month in Bangkok by a clear margin – about 336 mm, roughly fourteen times the January figure – and the cheapest. The temperature sits at 31°C, the city is green, the flooding is at its most frequent, and hotel rates are at their annual floor. It is the month for people who want Bangkok cheaply and do not mind getting wet.
The wettest month
September is the peak of the southwest monsoon over central Thailand, and the difference from the other wet months is real: more days with rain, longer falls, and a higher chance that a downpour arrives outside the usual late-afternoon window.
It still is not continuous rain. But the sensible assumption in September is that you will lose part of most days, rather than an hour of some of them, and the itinerary should be built accordingly – short outdoor blocks, indoor fallbacks close by, nothing that cannot be moved.
Flooding, properly
September and October are when Bangkok flooding is most likely, and it is worth being specific rather than vague:
- Street flooding after a heavy fall is routine – 30–50 cm in low-lying sois, usually draining within a couple of hours.
- The Chao Phraya runs high, and riverside walkways and piers can flood at high tide, especially when heavy rain coincides with a spring tide.
- Road traffic becomes extremely bad during and after. The BTS and MRT are elevated or underground and keep running; use them.
- Do not walk through floodwater – open drains, invisible kerbs, street run-off and an electrical risk near poles.
- Serious city-wide flooding is rare rather than annual, but localised flooding in September is normal and should be planned for.
Weather
September averages about 31°C by day and 25°C at night, with roughly 336 mm of rain. Humidity is at its highest of the year, and the cloud keeps daytime temperatures down.
What September is for
- Price. The cheapest month of the Bangkok year, by some distance.
- Indoor Bangkok at its best – this is a city with world-class malls, museums, galleries, cinemas, spas and covered markets, and September is when you use all of them.
- The Vegetarian Festival may begin at the end of the month – nine days of meat-free eating observed by the Chinese-Thai community, with Yaowarat turning almost entirely vegetarian and yellow flags marking participating stalls. Dates follow the lunar calendar and usually fall late September or October.
- Green city, at its lushest.
- Empty temples – the lowest visitor numbers of the year.
Prices and crowds
The annual floor. September is the cheapest month in Bangkok and among the quietest, with the summer visitors gone and the cool season still two months away. For anyone flexible on weather, it is the best value in the calendar.
See the Bangkok travel budget.
What to pack
Quick-drying everything, footwear you can rinse and will not slip in, a compact umbrella, a proper dry bag for electronics and documents, and strong insect repellent. Temple cover for shoulders and knees, and a layer for air conditioning. See what to pack for Thailand.
The September 2027 calendar
- Through September – the wettest month at about 336 mm; the monsoon at its peak over central Thailand.
- Through September – the highest likelihood of street flooding; the Chao Phraya runs high.
- Through September – the annual floor for hotel rates and visitor numbers.
- Late September or October – the Vegetarian Festival begins; Yaowarat turns vegetarian for nine days.
- Through September – Vassa continues until October.
- Through September – peak humidity; 31°C with heavy cloud.
- November – the cool season and Loy Krathong are ahead.
Read alongside
- Bangkok in August – Mother’s Day and the building rains.
- Bangkok in October – the rains ending and the season turning.
- Thailand in September – the country-level view.
- Best time to visit Bangkok – all twelve months compared.
- Getting around Bangkok – why the BTS is the wet-season answer.
- Bangkok travel budget – the cheapest month.
- Things to do in Bangkok – the indoor list, which September needs.
Frequently asked
How much does it rain in Bangkok in September?
About 336 mm – the wettest month by a clear margin, and roughly fourteen times the January figure. Expect to lose part of most days rather than an hour of some of them.
Is September a bad time to visit Bangkok?
It is the wettest and the cheapest. If you build the itinerary around short outdoor blocks with indoor fallbacks nearby, it works well – and the city is green, quiet and at its annual price floor.
Will Bangkok flood in September?
Localised street flooding after heavy falls is routine, typically 30–50 cm in low-lying sois and draining within a couple of hours. Serious city-wide flooding is rare rather than annual. The Chao Phraya runs high and riverside walkways can flood at high tide.
How do I get around when it floods?
The BTS and MRT, which are elevated or underground and keep running. Road traffic becomes extremely bad during and after heavy rain, and walking through floodwater is not safe.
How hot is Bangkok in September?
About 31°C by day and 25°C at night, with the highest humidity of the year. Cloud cover keeps daytime temperatures below the April peak.
What is the Vegetarian Festival?
Nine days of meat-free eating observed by the Chinese-Thai community, usually starting in late September or October following the lunar calendar. Yaowarat turns almost entirely vegetarian and yellow flags mark participating stalls.
Is September the cheapest month in Bangkok?
Yes, by some distance – the annual floor for both hotel rates and visitor numbers, with the summer visitors gone and the cool season still two months away.
Are the temples still worth visiting?
Very – they are at their quietest of the year and the grounds are green after months of rain. Go in the morning and keep an indoor option nearby for the afternoon.
You Might Also Love
Written by
John Morrison is the founder and lead travel writer at Packzup. Over the past decade he has explored destinations across Africa, the Americas, Asia, Europe, the Middle East, and Oceania — always self-funded, never on a press trip.
