Weather in Rotterdam in September

A good month. September works. It is not the peak, but nothing about it fights you. Highs average 18.9 °C, lows 12.9 °C, and rain falls on 13 days — nothing in the month is working against you.

September ranks 3 of 12 in Rotterdam. Only June scores clearly higher, and the difference is small enough to be settled by price rather than weather.

Rain on 13 days, 1 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; the day barely swings — 5.9 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 29.8 °C and the coldest night fell to 7.2 °C, and the wettest single day dropped 28 mm — roughly 40% of the month's rain in one day.

September is moderately variable: 23 mm in the driest year against 192 mm in the wettest, around an average of 70 mm. Roughly two Septembers in three land near that average, and the third does something else entirely.

Wind is light at 14 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 80%, high enough to notice on the warm days without dominating them.

How September sits in the year

The month is on the way down: 2.4 °C cooler than August, with October dropping another 4.1 °C. The first week and the last are not the same trip.

Daylight in September

12.8 hours of daylight, losing 2 hours across the month. That is between Rotterdam's extremes of 16.7 and 7.8 hours, so days are long enough not to constrain the plan.

Sea temperature

The sea sits at about 17.3 °C in September — cold — a quick dip rather than a swim, and a wetsuit if you are in for longer. This is the warmest the water gets all year.

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 Rotterdam versus nearby

If Rotterdam is one option among several, the nearby comparison is worth making. Breda is close enough to be a coin toss — within a degree on temperature, 1 day less rain. Lille is close enough to be a coin toss — within a degree on temperature, 2 days less rain.

So: September is effectively as good as it gets here — 2 points behind June, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Rotterdam

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