Bangkok (Krung Thep) weather in September

Regulars split the month cleanly: early November still carries occasional late-afternoon showers lasting about an hour, hot but not oppressive, while mid-November marks the real start of the cool season, with nights capable of dropping to the low 20s or even high teens Celsius even as daytime highs stay well over 30C. Our row backs that transition, 33.3C reading as a hot 38C, over 25.3C nights, with 69.2mm of rain across 10.1 days. Regulars call this an excellent overall window - the wet season essentially over, crowds not yet built to peak-season size - with the back half of the month the more reliably dry and comfortable half to target. The record: humidity 74 percent, 9.2 hours of sun, an 11.7 kph wind and AQI 101.

March is the hottest month here - 35.1C reading as 40C at 71 percent humidity, with nights that hold 26.9C - and it sits inside the season travellers know as the burning months. Regulars draw a distinction worth carrying: the crop and forest burning that ruins March in the north is a northern problem, while this city's haze is traffic, construction and industry, and it is there all year. Our column supports them: AQI 109 now against 101 in November and 154 in January, so the worst air here belongs to the cool season, not the burning one. Rain is not yet a factor at 37.4mm across 5.5 days. The record: 10.8 hours of sun and a 15.2 kph wind.

February is the cool season and by temperature the most pleasant stretch of the Bangkok year - 34C by day is still 38C to walk in, but nights fall to 25C and rain has stopped at 23.5mm across 4.3 days. The board's warning is about the same weather from the other side: the cool dry months from December to February are when a temperature inversion sits over the city and holds the traffic and construction dust down, which is why our AQI reads 125 now. They separate it from the northern smoke season, which is a March forest-burning problem rather than this one, and they say early February usually beats late February. The record: humidity 69 percent, 10.7 hours of sun and a 13.1 kph wind.

Bangkok-forum regulars are close to unanimous about April: it is the month they avoid. One writes that April is definitely their least favourite month to visit, "too damn hot", another lists March through May as brutally hot, and the standing recommendation is mid-October through December, when the weather settles and the crowds thin. Songkran splits opinion - regulars point out you can stay dry by avoiding the bar districts and the moat, while others simply leave town for the week. April's record: 36.2C days, 27.6C nights, humidity around 71 percent, nine precipitation days and 10.8 hours of sun, with AQI near 109.