Weather in Bangkok in September

A hard month. September asks something of you. Go in knowing what. You should expect rain on 27 days of the month, which is more days wet than dry.

September ranks 6 of 12 in Bangkok: past the worst of the year but short of December, which is the month to book if the dates are open.

Rain on 27 of the month's 30 days, 10 of them heavy. At that frequency a wet-weather backup is not a contingency, it is the itinerary — book the indoor things first and treat the clear days as the bonus. Natural fibres and a second shirt for the day. At 85% nothing dries, including you.

What the averages hide

Averages flatten a month, and this one hides a few things: 20 days top 30 °C, making the heat continuous rather than occasional. Across the twenty years measured, the hottest September day reached 34.8 °C and the coldest night fell to 21.7 °C, and the wettest single day dropped 114 mm — roughly 41% of the month's rain in one day.

September is one of the reliable ones — rainfall has stayed between 203 mm and 407 mm across all twenty years, a narrow enough band that the 278 mm average is something you can plan against rather than merely quote.

Wind is light at 5.8 km/h, so the temperature on the page is close to the temperature on your skin, and humidity at 85% is the real story though — it is the number that decides how the day feels, not the 30.6 °C.

How September sits in the year

Temperatures hold steady either side: 31.5 °C in August, 30.6 here, 30.5 in October. Nothing about the timing within the month matters much. Rain is the thing that moves: October brings 5 days less of it, so pushing the dates later buys drier weather.

Daylight in September

Bangkok sits close enough to the equator that daylight barely moves all year — 12.2 hours in September, against a range of just 1.6 hours across the whole calendar. Sunrise and sunset land at roughly the same time whenever you come.

An inland climate

Despite being inland, the year stays fairly even: 17.1 °C between the year's warmest afternoons and coldest nights.

How busy it gets

Off season. The genuine off season: cheapest by a distance, with the caveat that some tours and restaurants close entirely.

Crowd levels are estimated from climate desirability and school-holiday calendars, not from visitor numbers.

September in Bangkok versus nearby

If Bangkok is one option among several, the nearby comparison is worth making. Lat Krabang is close enough to be a coin toss — within a degree on temperature, 1 day less rain. Hua Hin is close enough to be a coin toss — within a degree on temperature, 1 day more rain.

So: September is a compromise. December is 35 points better and is what Bangkok is actually like at its best — worth moving the trip for if that is possible, and worth adjusting expectations for if it is not.

Every month in Bangkok

See all twelve months in Bangkok, or where else to go in September.