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 daytime maximum temperatures of 16°C in Belfast, Northern Ireland in September based on long-term weather averages. There are 4 hours of sunshine per day on average with 17 days with some rainfall and typically 94 mm of rainfall in the month.

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)