Weather in Seoul in September

Prime time. September is about as good as Seoul gets. Highs average 24.7 °C, lows 16.7 °C, and rain falls on 10 days — nothing in the month is working against you.

September ranks 4 of 12 in Seoul: past the worst of the year but short of May, which is the month to book if the dates are open.

Rain on 10 days, 4 of them heavy. Enough to need a plan B, not enough to need a plan around it. Nothing specialised needed — this is the month you pack for the trip rather than for the weather.

What the averages hide

Averages flatten a month, and this one hides a few things: it never really gets hot: not one day in an average September reaches 30 °C. Across the twenty years measured, the hottest September day reached 29.7 °C and the coldest night fell to 8.8 °C, and the wettest single day dropped 94 mm — roughly 68% of the month's rain in one day.

September is moderately variable: 32 mm in the driest year against 419 mm in the wettest, around an average of 138 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind is light at 9.1 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 79%, high enough to notice on the warm days without dominating them.

How September sits in the year

The month is on the way down: 3.8 °C cooler than August, with October dropping another 6 °C. The first week and the last are not the same trip. Rain has already shifted: 7 days fewer than August had.

Daylight in September

12.5 hours of daylight, losing 1.2 hours across the month. That is between Seoul's extremes of 14.7 and 9.6 hours, so days are long enough not to constrain the plan.

An inland climate

With no coast nearby, the year swings a fair way — 35.2 °C between the warmest afternoons and the coldest nights, wider than any coastal city at this latitude would manage.

How busy it gets

Peak season. Expect the highest prices of the year and to be booking well ahead.

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

September in Seoul versus nearby

If Seoul is one option among several, the nearby comparison is worth making. Daegu is close enough to be a coin toss — within a degree on temperature, 1 day more rain. Gwangju is close enough to be a coin toss — within a degree on temperature, the same number of rain days.

So: September is effectively as good as it gets here — 5 points behind May, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Seoul

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