Belfast weather in September 2025

Q: How warm is it in Belfast in September?

Daytime temperatures usually reach 16°C in Belfast in September, falling to 9°C at night.

Q: How sunny is it in Belfast in September?

There are normally 4 hours of bright sunshine each day in Belfast in September - that's 30% of daylight hours.

Q: How warm is the sea around Belfast in September?

The average sea temperature around Belfast in September is 14°C.

Q: Does it rain in Belfast in September?

There are usually 17 days with some rain in Belfast in September and the average monthly rainfall is 94mm.

Expect 16°C daytime maximum temperatures in the shade with on average 4 hours of sunshine per day in Belfast in September. Check more long-term weather averages for Belfast in September before you book your next holiday to Northern Ireland in 2025/2026.

16
16°C max day temperature
4
4 hours of sunshine per day
17
17 days with some rainfall
9
9°C min night temperature
13
13 hours of daylight per day
0
No heat & humidity
94
94 mm of monthly rainfall
3
3 (Moderate) UV index
14
14°C sea temperature

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The September weather guide for Northern Ireland (Belfast) shows long term weather averages processed from data supplied by CRU (University of East Anglia), the Met Office & the Netherlands Meteorological Institute. Find out more about our data sources.

Metric (°C / mm) | Imperial (°F / inches)