Weather in Hanoi in September

A hard month. September is a hard month in Hanoi, and worth planning around. You should expect rain on 18 days of the month, which is more days wet than dry.

September ranks 8 of 12 in Hanoi: past the worst of the year but short of December, which is the month to book if the dates are open.

This is wet-season rain: 18 wet days and 7 genuinely heavy ones, which in this climate means concentrated downpours rather than all-day grey. The pattern is usually a clear morning and a loud afternoon, so front-load the day and stop fighting the 3pm hour. 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: 22 days top 30 °C, making the heat continuous rather than occasional. Across the twenty years measured, the hottest September day reached 35.2 °C and the coldest night fell to 16.9 °C, and the wettest single day dropped 116 mm — roughly 52% of the month's rain in one day.

September is statistically steady but not small: the year-to-year variation is modest in relative terms, yet the wettest September on record still delivered 325 mm against 117 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 223 mm average is a reasonable planning figure, not a promise.

Wind is light at 5.5 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 31 °C.

How September sits in the year

Temperatures hold steady either side: 31.8 °C in August, 31 here, 28.5 in October. Nothing about the timing within the month matters much. Rain is the thing that moves: October brings 7 days less of it, so pushing the dates later buys drier weather.

Daylight in September

12.3 hours of daylight, losing 0.6 hours across the month. That is between Hanoi's extremes of 13.4 and 10.9 hours, so days are long enough not to constrain the plan.

An inland climate

Despite being inland, the year stays fairly even: 21.2 °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 Hanoi versus nearby

If Hanoi is one option among several, the nearby comparison is worth making. Haiphong is close enough to be a coin toss — within a degree on temperature, 1 day more rain. Thanh Hóa is close enough to be a coin toss — within a degree on temperature, 2 days more rain.

So: September is a compromise. December is 49 points better and is what Hanoi 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 Hanoi

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