Dún Laoghaire weather in September
Temperature, sea and sunshine in September: long-term averages from 30 years of weather data, not a forecast.
Holiday weather in September
Poor
Best time to visit: April – September
What is the weather like in Dún Laoghaire in September?
In September, Dún Laoghaire is mild: daytime highs average 17 °C, and nights cool down to about 12 °C. The sea averages 14.7 °C – swimming is only for the hardy. Expect around 4 hours of sunshine a day. Rain is frequent, with about 12 rainy days and 67 mm in total. All in all, September is not an ideal month for a holiday in Dún Laoghaire.
September compared
How the weather changes from August to October. Tap a month to open it.
| AugustAug | SeptemberSep | OctoberOct | |
|---|---|---|---|
| Score | 14 | 13 | 9 |
| Day | 18° | 17° | 14° |
| Night | 13° | 12° | 9° |
| Sea | 15° | 15° | 14° |
| Sun | 5 h | 4 h | 3 h |
| Rain days | 13 | 12 | 13 |
More details for September
- Daylight
- 12 h 47 min06:56 – 19:43
- UV index
- 3 · moderateclear sky, noon (estimate)All months
- Muggy days
- 0 daysdew point 18 °C or moreAll months
- Wind
- 21 km/haverage daily peakAll months
- Cloud cover
- 73 %on averageAll months
- Hot days
- 0 days30 °C or more
- Snow days
- 0 days1 cm or more of fresh snow
- Time zone
- UTC+1Europe/Dublin
How the score comes together
- Temperatureweight 35 %0 %
- Seaweight 25 %0 %
- Sunshineweight 20 %20 %
- Few rainy daysweight 20 %45 %
Each factor is rated from 0 to 100 % and weighted for the travel style “Sun, sea & sand”.
What to pack in September
- Sunscreen
- A jumper for the evenings
- Rain jacket or umbrella
Dún Laoghaire in September: quick answers
Is Dún Laoghaire hot in September?
No. In September, Dún Laoghaire is mild: daytime highs average 17 °C and nights drop to about 12 °C.
Can you swim in Dún Laoghaire in September?
Only if you don't mind cold water: in September the sea averages just 14.7 °C. Comfortable swimming temperatures are not reached at any time of year.
Does it rain much in Dún Laoghaire in September?
Rain is frequent, with about 12 rainy days and 67 mm in total.
Dún Laoghaire month by month
The whole year in Dún LaoghaireAll destinations: IrelandWhere to go in SeptemberSea temperature in September
Climate averages 1996–2025, not a forecast. Data: Copernicus ERA5 / ERA5-Land via Open-Meteo.com (CC BY 4.0), NOAA OISST, WMO 1991–2020 (NOAA NCEI), GeoNames (CC BY 4.0). Sources & licences