Belfast 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
Fair
Best time to visit: June – August
What is the weather like in Belfast in September?
In September, Belfast is cool: daytime highs average 16 °C, and nights cool down to about 12 °C. The sea averages 14.0 °C – swimming is only for the hardy. Expect around 4 hours of sunshine a day. Rain is frequent, with about 14 rainy days and 80 mm in total. All in all, September is a so-so month for a holiday in Belfast.
September compared
How the weather changes from August to October. Tap a month to open it.
| AugustAug | SeptemberSep | OctoberOct | |
|---|---|---|---|
| Score | 57 | 50 | 31 |
| Day | 17° | 16° | 13° |
| Night | 13° | 12° | 10° |
| Sea | 14° | 14° | 14° |
| Sun | 5 h | 4 h | 3 h |
| Rain days | 15 | 14 | 15 |
More details for September
- Daylight
- 12 h 49 min06:54 – 19:44
- UV index
- 3 · moderateclear sky, noon (estimate)All months
- Muggy days
- 0 daysdew point 18 °C or moreAll months
- Wind
- 24 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/London
How the score comes together
- Temperatureweight 50 %75 %
- Sunshineweight 20 %17 %
- Few rainy daysweight 30 %31 %
Each factor is rated from 0 to 100 % and weighted for the travel style “City break”.
What to pack in September
- Sunscreen
- A jumper for the evenings
- Rain jacket or umbrella
Belfast in September: quick answers
Is Belfast hot in September?
No. In September, Belfast is cool: daytime highs average 16 °C and nights drop to about 12 °C.
Can you swim in Belfast in September?
Only if you don't mind cold water: in September the sea averages just 14.0 °C. Comfortable swimming temperatures are not reached at any time of year.
Does it rain much in Belfast in September?
Rain is frequent, with about 14 rainy days and 80 mm in total.
Belfast month by month
The whole year in BelfastAll destinations: United KingdomWhere 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