September is one of the warmer months of the year in Derry, with average highs near 14.9°C and lows around 9.9°C (mean 12.4°C). It is about average for rainfall, averaging 103 mm of rainfall and 88% relative humidity across the period.
September is one of the warmer months of the year in Derry. Across 45 years of records, the warmest September in Derry was 2021 — when the month averaged 14.2°C — while the coldest was 1986 at 10.6°C. Typical September days reach 14.9°C with nights near 9.9°C. The long-term trend is warming, about 0.3°C per decade.
September is about average for rainfall in Derry, averaging 103 mm of rainfall. The wettest September on record was 1985 with 211 mm, while the driest was 2014 at 26 mm.
Relative humidity in Derry during September averages 88%. The most humid Septembers were 1985 and 2006 at 90%, and the least humid was 1984 at 86%.
September receives about 2.7 kWh/m²/day of solar energy in Derry. The sunniest September was 1991 at 3.2 kWh/m²/day, and the cloudiest was 2021 at 2.3.
Average wind speed in Derry during September is 4.3 m/s. The windiest September was 2011 at 5.6 m/s, while the calmest was 2014 at 2.9 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 11.7°C | 12.2°C | 12.8°C | 12.4°C | 13.1°C | +1.4°C |
| Avg High | 14.2°C | 14.7°C | 15.3°C | 14.8°C | 15.8°C | +1.6°C |
| Avg Low | 9.2°C | 9.6°C | 10.3°C | 9.9°C | 10.5°C | +1.3°C |
| Avg Rain | 120 mm | 92 mm | 100 mm | 103 mm | 100 mm | -20 mm |
September temperatures in Derry have risen by about 1.2°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 4.5°C (1986) to a record high of 24.1°C (2023).
Rainfall in September is about average for rainfall, averaging 103 mm, with a wettest year of 211 mm.
One of the best times to visit Derry
September is one of the best times to visit Derry. Expect days averaging 14.9°C and nights around 9.9°C (mean 12.4°C) — warmer than Derry's yearly average — with higher rainfall (103 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 | 15.0°C | 12.4°C | 9.8°C | 17.3°C | 6.2°C | 124 mm | 87% | 4.8 m/s | 2.6 |
| 2024 | 14.8°C | 12.1°C | 9.4°C | 20.3°C | 7.0°C | 54 mm | 88% | 4.1 m/s | 2.9 |
| 2023 | 16.9°C | 14.1°C | 11.3°C | 24.1°C | 8.5°C | 127 mm | 88% | 4.1 m/s | 2.8 |
| 2022 | 15.8°C | 13.3°C | 10.9°C | 19.4°C | 8.4°C | 127 mm | 86% | 3.9 m/s | 2.8 |
| 2021 🔥 | 17.0°C | 14.2°C | 11.4°C | 22.2°C | 7.8°C | 83 mm | 89% | 3.4 m/s | 2.3 |
| 2020 | 15.2°C | 12.6°C | 9.9°C | 19.5°C | 5.1°C | 86 mm | 88% | 4.3 m/s | 2.8 |
| 2019 | 15.2°C | 12.8°C | 10.4°C | 18.6°C | 8.4°C | 120 mm | 88% | 4.1 m/s | 2.8 |
| 2018 | 13.9°C | 11.4°C | 8.9°C | 18.6°C | 5.2°C | 95 mm | 86% | 4.8 m/s | 2.5 |
| 2017 | 14.4°C | 12.0°C | 9.6°C | 19.6°C | 6.5°C | 134 mm | 88% | 4.7 m/s | 2.5 |
| 2016 | 15.5°C | 13.1°C | 10.7°C | 19.4°C | 7.2°C | 100 mm | 89% | 4.7 m/s | 2.4 |
| 2015 | 14.0°C | 11.5°C | 9.0°C | 17.2°C | 6.2°C | 61 mm | 89% | 3.9 m/s | 2.8 |
| 2014 | 16.2°C | 13.3°C | 10.4°C | 19.4°C | 8.1°C | 26 mm | 89% | 2.9 m/s | 2.8 |
| 2013 | 14.9°C | 12.5°C | 10.0°C | 20.0°C | 6.4°C | 78 mm | 88% | 4.4 m/s | 2.6 |
| 2012 | 13.7°C | 11.5°C | 9.3°C | 18.8°C | 6.1°C | 114 mm | 87% | 5.2 m/s | 2.7 |
| 2011 | 15.0°C | 12.7°C | 10.4°C | 20.1°C | 8.2°C | 150 mm | 88% | 5.6 m/s | 2.6 |
| 2010 | 15.1°C | 12.7°C | 10.3°C | 19.3°C | 4.7°C | 155 mm | 89% | 4.5 m/s | 2.7 |
| 2009 | 14.8°C | 12.5°C | 10.2°C | 17.4°C | 7.2°C | 59 mm | 89% | 4.5 m/s | 2.8 |
| 2008 | 14.5°C | 12.2°C | 9.8°C | 17.3°C | 6.8°C | 128 mm | 88% | 3.9 m/s | 2.6 |
| 2007 | 14.9°C | 12.3°C | 9.8°C | 18.8°C | 5.8°C | 83 mm | 88% | 4.2 m/s | 2.7 |
| 2006 | 16.7°C | 13.9°C | 11.1°C | 20.1°C | 7.4°C | 155 mm | 90% | 4.3 m/s | 2.7 |
| 2005 | 15.9°C | 13.2°C | 10.6°C | 20.9°C | 6.7°C | 94 mm | 88% | 4.9 m/s | 2.6 |
| 2004 | 15.3°C | 12.9°C | 10.6°C | 19.6°C | 8.7°C | 132 mm | 89% | 5.4 m/s | 2.7 |
| 2003 | 15.3°C | 12.7°C | 10.1°C | 20.0°C | 6.6°C | 87 mm | 88% | 3.7 m/s | 2.5 |
| 2002 | 15.6°C | 12.9°C | 10.2°C | 18.7°C | 7.0°C | 44 mm | 88% | 3.4 m/s | 2.8 |
| 2001 | 14.8°C | 12.5°C | 10.2°C | 18.4°C | 6.8°C | 73 mm | 88% | 4.4 m/s | 2.6 |
| 2000 | 15.5°C | 12.9°C | 10.3°C | 19.9°C | 7.0°C | 146 mm | 89% | 3.9 m/s | 2.4 |
| 1999 | 15.7°C | 13.0°C | 10.4°C | 21.3°C | 6.1°C | 175 mm | 89% | 4.5 m/s | 2.4 |
| 1998 | 15.4°C | 13.0°C | 10.5°C | 20.2°C | 7.8°C | 81 mm | 90% | 4.1 m/s | 2.7 |
| 1997 | 15.1°C | 12.4°C | 9.8°C | 18.0°C | 6.8°C | 72 mm | 87% | 4.5 m/s | 2.9 |
| 1996 | 15.7°C | 12.9°C | 10.0°C | 19.5°C | 7.2°C | 54 mm | 88% | 4.1 m/s | 3 |
| 1995 | 14.6°C | 12.4°C | 10.2°C | 17.8°C | 7.0°C | 93 mm | 88% | 4 m/s | 2.8 |
| 1994 | 13.8°C | 11.5°C | 9.3°C | 18.3°C | 6.7°C | 88 mm | 87% | 3.9 m/s | 2.9 |
| 1993 | 13.9°C | 11.4°C | 8.8°C | 17.9°C | 6.1°C | 89 mm | 87% | 4 m/s | 2.5 |
| 1992 | 13.1°C | 10.7°C | 8.2°C | 17.4°C | 5.8°C | 125 mm | 87% | 4.3 m/s | 2.9 |
| 1991 | 15.8°C | 12.9°C | 10.0°C | 21.7°C | 5.0°C | 74 mm | 86% | 4.2 m/s | 3.2 |
| 1990 | 13.9°C | 11.4°C | 8.9°C | 19.3°C | 5.5°C | 69 mm | 86% | 4.5 m/s | 2.5 |
| 1989 | 14.6°C | 11.8°C | 9.1°C | 17.8°C | 6.4°C | 58 mm | 86% | 4.1 m/s | 2.5 |
| 1988 | 13.8°C | 11.6°C | 9.4°C | 19.9°C | 6.0°C | 131 mm | 88% | 5 m/s | 2.4 |
| 1987 | 13.9°C | 11.5°C | 9.1°C | 17.1°C | 5.0°C | 104 mm | 86% | 5 m/s | 2.8 |
| 1986 ❄️ | 13.4°C | 10.6°C | 7.8°C | 17.2°C | 4.5°C | 33 mm | 86% | 4 m/s | 2.9 |
| 1985 🌧️ | 15.0°C | 12.6°C | 10.2°C | 19.4°C | 7.1°C | 211 mm | 90% | 4.1 m/s | 2.5 |
| 1984 | 13.9°C | 11.7°C | 9.5°C | 19.3°C | 6.3°C | 131 mm | 86% | 4.3 m/s | 2.6 |
| 1983 | 14.2°C | 11.7°C | 9.2°C | 19.0°C | 4.6°C | 115 mm | 87% | 5.2 m/s | — |
| 1982 | 14.2°C | 11.5°C | 8.8°C | 19.7°C | 4.8°C | 124 mm | 87% | 4.8 m/s | — |
| 1981 | 15.0°C | 12.5°C | 10.0°C | 20.2°C | 7.8°C | 170 mm | 89% | 4.5 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 14.9°C with lows near 9.9°C (mean 12.4°C), based on 45 years of NASA POWER data.
September averages 103 mm of rainfall in Derry, about average for rainfall. The wettest on record was 211 mm in 1985.
The hottest September reached 24.1°C in 2023. The coldest dipped to 4.5°C in 1986.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.2°C. Daytime highs moved from 14.5°C to 15.9°C and overnight lows from 9.5°C to 10.6°C over the same span.
September is one of the warmer months of the year in Derry and about average for rainfall, so plan for around 14.9°C daytime highs and 9.9°C at night.
Not quite — September is the 10th coolest month in Derry, averaging 12.4°C.
For September in Derry, pack light layers you can adjust through the day, with typical highs of 14.9°C and lows of 9.9°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 88% — quite humid.
Average wind speed in September is 4.3 m/s. The windiest September on record averaged 5.6 m/s (2011).
The wettest September on record was 1985 with 211 mm. On average, September sees 103 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 Derry 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.
