Weather in Dublin in September

A good month. September works. It is not the peak, but nothing about it fights you. Highs average 16.3 °C, lows 11.2 °C, and rain falls on 13 days — nothing in the month is working against you.

September ranks 2 of 12 in Dublin. Only July scores clearly higher, and the difference is small enough to be settled by price rather than weather.

Rain on 13 days, 2 of them heavy. Enough to need a plan B, not enough to need a plan around it. Pack for 16.3 °C days and 11.2 °C nights; the spread matters more here than any single number.

What the averages hide

Averages flatten a month, and this one hides a few things: the day barely swings — 5.2 °C between the overnight low and the afternoon high. Across the twenty years measured, the hottest September day reached 21.7 °C and the coldest night fell to 6.3 °C, and the wettest single day dropped 44 mm — roughly 58% 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 148 mm against 16 mm in the driest. In a month this wet, even a tame spread is a lot of rain in absolute terms — the 76 mm average is a reasonable planning figure, not a promise.

Wind is light at 15.3 km/h, so the temperature on the page is close to the temperature on your skin, and humidity runs at 87%, high enough to notice on the warm days without dominating them.

How September sits in the year

The month is on the way down: 1.6 °C cooler than August, with October dropping another 2.8 °C. The first week and the last are not the same trip.

Daylight in September

12.8 hours of daylight, losing 2.1 hours across the month. That is between Dublin's extremes of 17 and 7.6 hours, so days are long enough not to constrain the plan.

An inland climate

Despite being inland, the year stays fairly even: 13.9 °C between the year's warmest afternoons and coldest nights.

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 Dublin versus nearby

If Dublin is one option among several, the nearby comparison is worth making. Galway is close enough to be a coin toss — within a degree on temperature, 3 days more rain. Cork is close enough to be a coin toss — within a degree on temperature, 2 days more rain.

So: September is effectively as good as it gets here — 0 points behind July, which is inside the margin where the weather stops being the deciding factor and price starts being it.

Every month in Dublin

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