Climate averages 1991–2020
Belfast weather
in September.
A mild, moderately wet month: the 4th warmest and the joint 4th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
September is a mild month in Belfast: daytime highs average 15.7°C and nights cool to about 11.3°C. By daytime temperature it is the 4th warmest of the 12 months.
Expect about 70 mm of rain on roughly 13 days, which makes September a moderately wet month (the joint 4th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 12 h 47 min on an average September day.
The nearest other city in this atlas is Lisburn (11 km away). In September its highs average 15.6°C, about as warm as Belfast, with 70 mm of rain.
Among the 143 cities listed in the United Kingdom, Belfast ranks joint 131st of 143 for the warmest September highs and joint 118th of 143 for the driest September (rainfall, lowest first). The mean September high of those 143 cities is 17.3°C; Belfast is 1.6°C cooler than that mean.
From September to October, average highs fall by 2.9°C to 12.8°C, and monthly rainfall rises from 70 mm to 86 mm.
The annual picture
September in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Belfast climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 7.5°C3.9°C | 3.9°C | 77 | 14.2 | 7.98 h |
| February | 7.7°C3.8°C | 3.8°C | 63 | 12.2 | 9.710 h |
| March | 9.1°C4.4°C | 4.4°C | 62 | 13.4 | 11.812 h |
| April | 10.9°C5.9°C | 5.9°C | 65 | 13.0 | 14.014 h |
| May | 13.6°C8.2°C | 8.2°C | 70 | 14.1 | 16.016 h |
| June | 15.9°C10.9°C | 10.9°C | 75 | 13.2 | 17.217 h |
| July | 17.4°C12.5°C | 12.5°C | 81 | 14.6 | 16.717 h |
| August | 17.3°C12.6°C | 12.6°C | 81 | 14.2 | 14.915 h |
| September, selected | 15.7°C11.3°C | 11.3°C | 70 | 12.5 | 12.813 h |
| October | 12.8°C9.0°C | 9.0°C | 86 | 13.5 | 10.611 h |
| November | 9.8°C6.4°C | 6.4°C | 85 | 14.0 | 8.59 h |
| December | 7.9°C4.4°C | 4.4°C | 82 | 13.5 | 7.47 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
September in nearby cities
- Lisburn in SeptemberUnited Kingdom · 11 kmHigh 15.6°C · Low 10.6°C · 70 mm rain
- Derry in SeptemberUnited Kingdom · 99 kmHigh 15.4°C · Low 10.4°C · 75 mm rain
- Douglas in SeptemberIsle of Man · 106 kmHigh 15.1°C · Low 13.1°C · 85 mm rain
- Dublin in SeptemberIreland · 142 kmHigh 16.5°C · Low 11.0°C · 70 mm rain
- Tallaght in SeptemberIreland · 149 kmHigh 16.1°C · Low 10.5°C · 70 mm rain
- Paisley in SeptemberUnited Kingdom · 167 kmHigh 15.1°C · Low 9.4°C · 90 mm rain
- East Kilbride in SeptemberUnited Kingdom · 171 kmHigh 14.4°C · Low 8.4°C · 83 mm rain
- Glasgow in SeptemberUnited Kingdom · 176 kmHigh 15.1°C · Low 9.2°C · 83 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Belfast) is explained once on the Belfast year overview and on the Sources, method and limits page.
Lisburn lies in the same rainfall cell, so its rainfall figures are identical to these; temperatures differ because they come from smaller 0.1° cells.