Weather in Belfast in September 2025
Average weather
Average temperature in Belfast in September
The expected average maximum temperature in September is +18°C with a maximum of +25°C and a minimum of +7°C.
The average maximum temperature goes down 6% by the end of the month, compared with the beginning of the month, from +17°C to +16°C.
Is Belfast warm or cold in September?
Belfast is typically mild in September.
Maximum temperatures go down compared to the previous month from +18°C to +16°C. The minimum temperature also goes down from +12°C to +10°C.
Pack a light jacket as it will be warm in the day and cool in the evenings.
Take a look at how September is compared to other months in Belfast:
Water temperature in Belfast in September
Water in Belfast in September is Cold. It varies from +14°C to +15°C, with an average of +14°C. This is almost similar to the air temperature, which averages +16°C.
The water temperature in September is one of the warmest of the entire year:
Can you swim in Belfast in September?
Climate in Belfast in September
| August | September | October | ||||
|---|---|---|---|---|---|---|
| Avg. temperature | ||||||
| +18°C | +16°C | +13°C | ||||
| Min. temperature | ||||||
| +3°C | +1°C | -2°C | ||||
| Max. temperature | ||||||
| +29°C | +25°C | +21°C | ||||
| Rainfall | ||||||
| 82 mm | 72 mm | 91 mm | ||||
| Wind | ||||||
| 3 m/s | 4 m/s | 4 m/s | ||||
| Avg. water temperature | ||||||
| +14°C | +14°C | +13°C | ||||
| Humidity | ||||||
| 81% | 82% | 84% | ||||
| Air pressure | ||||||
| 1012 HPa | 1013 HPa | 1009 HPa | ||||
| Sunny days | ||||||
| 1 | 2 | 1 | ||||
| Cloudy days | ||||||
| 9 | 10 | 11 | ||||
| Rainy days | ||||||
| 21 | 18 | 19 | ||||
| Snowy days | ||||||
| 0 | 0 | 0 | ||||
September weather is still as ok as in August. It’s getting colder in September. From +18°C in the day, the average maximum temperature lowers to +16°C. As September arrives, the amount of rainfall goes down. On average, the rainfall volume decreases from 82 mm to 72 mm. Humidity rises from 81% to 82%. Winds are stronger in comparison to August, going up from 3 m/s to 4 m/s on average. The good news is there are likely to be more sunny days in September, from 1 to 2.
October brings much the same weather, it remains ok.
Wind
The average wind speed is 4 m/s getting up to 8 m/s which is a medium breeze. You can feel it, especially getting out of the water.
The average wind speed in Belfast is gradually increasing during September, going from 3 m/s to 4 m/s over the course of the month.
Rain
How was the weather last September in Belfast?
Climate Change over Years
The climate in Belfast in September has not changed much over the last 43 years.
The average temperature was the lowest in 1979 (+11°C) and the highest in 1995 (+14°C). The driest year was 2003 with only 711 mm of rainfall, and the wettest year was 2019 with 1255 mm.
FAQ
Is September a good time to visit Belfast?
Can you sunbathe in Belfast in September?
Can you swim in Belfast in September?
Is Belfast rainy in September?
Is it sunny in Belfast in September?
Other cities in United Kingdom
Monthly weather in Belfast
Source of the data
For this page, we’ve looked at the typical weather in Belfast, based on historical hourly weather data from January 1, 1979, to December 31, 2023.
For past dates, we show actual recorded data at the location at that time. Forecasts are based on recorded weather during that day of the year, averaged over the total years for which we have records (unless stated otherwise). The daily temperature is the highest recorded temperature in the shadow during that day.