September is one of the warmer months of the year in Belfast, with average highs near 15.2°C and lows around 11°C (mean 13.1°C). It is about average for rainfall, averaging 89 mm of rainfall and 87% relative humidity across the period.
September is one of the warmer months of the year in Belfast. Across 45 years of records, the warmest September in Belfast was 2023 — when the month averaged 14.9°C — while the coldest was 1986 at 11.3°C. Typical September days reach 15.2°C with nights near 11°C. The long-term trend is warming, about 0.3°C per decade.
September is about average for rainfall in Belfast, averaging 89 mm of rainfall. The wettest September on record was 1981 with 170 mm, while the driest was 2014 at 10 mm.
Relative humidity in Belfast during September averages 87%. The most humid September was 1985 at 90%, and the least humid was 1986 at 84%.
September receives about 2.8 kWh/m²/day of solar energy in Belfast. The sunniest Septembers were 1991 and 2015 at 3.2 kWh/m²/day, and the cloudiest was 1985 at 2.3.
Average wind speed in Belfast during September is 4.6 m/s. The windiest Septembers were 1983 and 2011 at 5.7 m/s, while the calmest was 2014 at 3 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 12.5°C | 12.9°C | 13.5°C | 13.1°C | 13.9°C | +1.4°C |
| Avg High | 14.6°C | 15.0°C | 15.5°C | 15.2°C | 16.0°C | +1.4°C |
| Avg Low | 10.4°C | 10.8°C | 11.4°C | 11.0°C | 11.7°C | +1.3°C |
| Avg Rain | 100 mm | 78 mm | 82 mm | 88 mm | 105 mm | +4 mm |
September temperatures in Belfast have risen by about 1.3°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 6°C (1988) to a record high of 22.4°C (2023).
Rainfall in September is about average for rainfall, averaging 89 mm, with a wettest year of 170 mm.
One of the best times to visit Belfast
September is one of the best times to visit Belfast. Expect days averaging 15.2°C and nights around 11°C (mean 13.1°C) — warmer than Belfast's yearly average — with higher rainfall (89 mm), so conditions are generally comfortable for sightseeing and outdoor plans.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 15.5°C | 13.4°C | 11.3°C | 17.4°C | 9.1°C | 117 mm | 86% | 5 m/s | 2.8 |
| 2024 | 15.1°C | 13.0°C | 10.8°C | 19.6°C | 7.3°C | 57 mm | 87% | 4.6 m/s | 2.9 |
| 2023 🔥 | 17.2°C | 14.9°C | 12.7°C | 22.4°C | 9.2°C | 160 mm | 89% | 4.5 m/s | 2.8 |
| 2022 | 16.1°C | 14.1°C | 12.1°C | 18.2°C | 9.5°C | 127 mm | 86% | 4.5 m/s | 3 |
| 2021 | 16.8°C | 14.6°C | 12.4°C | 19.3°C | 8.9°C | 67 mm | 89% | 3.4 m/s | 2.6 |
| 2020 | 15.4°C | 13.2°C | 11.1°C | 20.0°C | 7.4°C | 98 mm | 87% | 4.5 m/s | 2.8 |
| 2019 | 15.6°C | 13.4°C | 11.2°C | 18.1°C | 9.1°C | 119 mm | 87% | 4.5 m/s | 2.8 |
| 2018 | 14.8°C | 12.5°C | 10.1°C | 18.4°C | 6.3°C | 74 mm | 85% | 5.2 m/s | 2.8 |
| 2017 | 14.9°C | 12.9°C | 10.9°C | 17.7°C | 8.7°C | 131 mm | 88% | 5 m/s | 2.6 |
| 2016 | 16.1°C | 14.0°C | 11.9°C | 20.1°C | 7.9°C | 94 mm | 88% | 5 m/s | 2.7 |
| 2015 | 14.4°C | 12.3°C | 10.1°C | 15.7°C | 8.2°C | 48 mm | 88% | 4.3 m/s | 3.2 |
| 2014 | 16.1°C | 13.9°C | 11.7°C | 18.5°C | 8.3°C | 10 mm | 89% | 3 m/s | 3 |
| 2013 | 14.9°C | 12.8°C | 10.8°C | 18.9°C | 8.3°C | 82 mm | 88% | 4.5 m/s | 2.6 |
| 2012 | 14.4°C | 12.3°C | 10.1°C | 18.3°C | 8.0°C | 109 mm | 87% | 5.3 m/s | 2.8 |
| 2011 | 15.4°C | 13.4°C | 11.3°C | 17.7°C | 8.3°C | 99 mm | 88% | 5.7 m/s | 2.8 |
| 2010 | 15.3°C | 13.4°C | 11.6°C | 18.2°C | 7.1°C | 117 mm | 87% | 4.8 m/s | 2.9 |
| 2009 | 15.4°C | 13.1°C | 10.8°C | 17.1°C | 7.8°C | 44 mm | 88% | 4.5 m/s | 2.9 |
| 2008 | 15.0°C | 13.0°C | 11.1°C | 16.8°C | 9.1°C | 105 mm | 89% | 4.3 m/s | 2.5 |
| 2007 | 15.2°C | 13.0°C | 10.8°C | 18.1°C | 6.4°C | 51 mm | 87% | 4.5 m/s | 2.8 |
| 2006 | 16.5°C | 14.6°C | 12.7°C | 19.0°C | 9.9°C | 113 mm | 89% | 4.6 m/s | 2.8 |
| 2005 | 15.8°C | 13.7°C | 11.5°C | 19.2°C | 8.7°C | 71 mm | 88% | 5 m/s | 2.7 |
| 2004 | 15.5°C | 13.6°C | 11.7°C | 19.4°C | 9.9°C | 105 mm | 88% | 5.6 m/s | 2.9 |
| 2003 | 15.9°C | 13.6°C | 11.4°C | 18.9°C | 8.2°C | 62 mm | 87% | 3.7 m/s | 2.9 |
| 2002 | 15.4°C | 13.5°C | 11.7°C | 17.1°C | 9.5°C | 50 mm | 88% | 3.3 m/s | 2.9 |
| 2001 | 15.0°C | 12.9°C | 10.9°C | 18.1°C | 7.8°C | 63 mm | 88% | 4.9 m/s | 2.8 |
| 2000 | 15.7°C | 13.7°C | 11.6°C | 18.7°C | 9.2°C | 150 mm | 89% | 4.4 m/s | 2.4 |
| 1999 | 16.0°C | 14.0°C | 12.0°C | 20.2°C | 8.2°C | 157 mm | 89% | 4.7 m/s | 2.7 |
| 1998 | 15.5°C | 13.6°C | 11.7°C | 18.4°C | 8.3°C | 76 mm | 90% | 4.6 m/s | 3 |
| 1997 | 15.2°C | 13.1°C | 11.0°C | 17.8°C | 8.1°C | 59 mm | 87% | 4.7 m/s | 2.8 |
| 1996 | 15.4°C | 13.1°C | 10.9°C | 19.5°C | 9.0°C | 34 mm | 87% | 4.3 m/s | 2.9 |
| 1995 | 15.3°C | 13.1°C | 10.9°C | 18.2°C | 8.0°C | 71 mm | 87% | 4.3 m/s | 3.1 |
| 1994 | 14.1°C | 12.1°C | 10.1°C | 17.6°C | 8.4°C | 65 mm | 87% | 4.1 m/s | 2.9 |
| 1993 | 14.1°C | 12.2°C | 10.2°C | 17.9°C | 6.8°C | 109 mm | 86% | 4.7 m/s | 2.6 |
| 1992 | 14.0°C | 12.0°C | 10.0°C | 16.8°C | 7.3°C | 102 mm | 87% | 4.9 m/s | 2.7 |
| 1991 | 15.7°C | 13.3°C | 10.9°C | 19.6°C | 7.0°C | 55 mm | 85% | 4.3 m/s | 3.2 |
| 1990 | 14.5°C | 12.3°C | 10.2°C | 19.0°C | 7.5°C | 49 mm | 84% | 4.7 m/s | 2.7 |
| 1989 | 15.1°C | 12.8°C | 10.6°C | 18.0°C | 8.5°C | 61 mm | 86% | 4.6 m/s | 2.4 |
| 1988 | 14.2°C | 12.3°C | 10.3°C | 18.0°C | 6.0°C | 94 mm | 87% | 5.3 m/s | 2.5 |
| 1987 | 14.2°C | 12.1°C | 10.1°C | 16.5°C | 7.6°C | 102 mm | 86% | 5 m/s | 2.7 |
| 1986 ❄️ | 13.7°C | 11.3°C | 8.9°C | 17.4°C | 6.1°C | 13 mm | 84% | 3.9 m/s | 2.9 |
| 1985 | 15.2°C | 13.1°C | 10.9°C | 18.2°C | 7.7°C | 139 mm | 90% | 4.4 m/s | 2.3 |
| 1984 | 14.6°C | 12.6°C | 10.7°C | 18.3°C | 7.6°C | 113 mm | 85% | 4.8 m/s | 2.5 |
| 1983 | 14.3°C | 12.3°C | 10.3°C | 16.9°C | 6.7°C | 95 mm | 87% | 5.7 m/s | — |
| 1982 | 14.7°C | 12.4°C | 10.1°C | 17.8°C | 6.9°C | 117 mm | 87% | 4.8 m/s | — |
| 1981 🌧️ | 15.4°C | 13.3°C | 11.3°C | 18.6°C | 8.6°C | 170 mm | 88% | 5.1 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 15.2°C with lows near 11°C (mean 13.1°C), based on 45 years of NASA POWER data.
September averages 89 mm of rainfall in Belfast, about average for rainfall. The wettest on record was 170 mm in 1981.
The hottest September reached 22.4°C in 2023. The coldest dipped to 6°C in 1988.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.3°C. Daytime highs moved from 14.8°C to 16.1°C and overnight lows from 10.7°C to 11.9°C over the same span.
September is one of the warmer months of the year in Belfast and about average for rainfall, so plan for around 15.2°C daytime highs and 11°C at night.
Not quite — September is the 10th coolest month in Belfast, averaging 13.1°C.
For September in Belfast, pack light layers you can adjust through the day, with typical highs of 15.2°C and lows of 11°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 87% — quite humid.
Average wind speed in September is 4.6 m/s. The windiest September on record averaged 5.7 m/s (1983).
The wettest September on record was 1981 with 170 mm. On average, September sees 89 mm.
All figures are derived from NASA POWER (Prediction Of Worldwide Energy Resources), based on MERRA-2 satellite reanalysis, covering 1981–2025.
Explore how the weather in Belfast behaves each September, based on 45 years of NASA POWER climate data from 1981 to 2025. This page breaks down average temperatures, rainfall, humidity, wind and solar radiation for September specifically, along with year-by-year records and how the month has changed over the decades.
