September is one of the warmer months of the year in Duncan, with average highs near 19.4°C and lows around 11.6°C (mean 15.5°C). It is one of the drier months, averaging 46 mm of rainfall and 76% relative humidity across the period.
September is one of the warmer months of the year in Duncan. Across 45 years of records, the warmest September in Duncan was 1995 — when the month averaged 17.3°C — while the coldest was 1984 at 13.4°C. Typical September days reach 19.4°C with nights near 11.6°C. The long-term trend is warming, about 0.3°C per decade.
September is one of the drier months in Duncan, averaging 46 mm of rainfall. The wettest September on record was 2013 with 104 mm, while the driest was 1993 at 2 mm.
Relative humidity in Duncan during September averages 76%. The most humid September was 2025 at 84%, and the least humid was 1993 at 71%.
September receives about 4 kWh/m²/day of solar energy in Duncan. The sunniest Septembers were 1989, 1999 and 2012 at 4.6 kWh/m²/day, and the cloudiest was 2019 at 3.3.
Average wind speed in Duncan during September is 1.2 m/s. The windiest September was 1992 at 1.5 m/s, while the calmest were 1987 and 1993 at 1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 14.6°C | 15.9°C | 15.3°C | 15.7°C | 16.2°C | +1.6°C |
| Avg High | 18.6°C | 20.0°C | 19.2°C | 19.5°C | 20.0°C | +1.4°C |
| Avg Low | 10.6°C | 11.7°C | 11.4°C | 11.9°C | 12.4°C | +1.8°C |
| Avg Rain | 45 mm | 30 mm | 39 mm | 62 mm | 55 mm | +9 mm |
September temperatures in Duncan have risen by about 1.8°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 5.3°C (1981) to a record high of 29.7°C (2017).
Rainfall in September is one of the drier months, averaging 46 mm, with a wettest year of 104 mm.
One of the best times to visit Duncan
September is one of the best times to visit Duncan. Expect days averaging 19.4°C and nights around 11.6°C (mean 15.5°C) — warmer than Duncan's yearly average — with moderate rainfall (46 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 | 19.7°C | 16.2°C | 12.8°C | 27.1°C | 9.4°C | 76 mm | 84% | 1.3 m/s | 3.9 |
| 2024 | 19.3°C | 15.6°C | 12.0°C | 27.9°C | 6.7°C | 48 mm | 79% | 1.2 m/s | 3.8 |
| 2023 | 19.9°C | 15.8°C | 11.7°C | 27.6°C | 7.6°C | 40 mm | 74% | 1.4 m/s | 4 |
| 2022 | 21.5°C | 17.2°C | 12.8°C | 27.9°C | 9.6°C | 10 mm | 73% | 1.2 m/s | 4.4 |
| 2021 | 18.4°C | 14.9°C | 11.5°C | 24.1°C | 8.5°C | 98 mm | 79% | 1.4 m/s | 3.6 |
| 2020 | 21.2°C | 17.2°C | 13.3°C | 28.3°C | 9.9°C | 56 mm | 77% | 1.2 m/s | 3.7 |
| 2019 | 18.7°C | 15.4°C | 12.1°C | 26.3°C | 7.2°C | 82 mm | 78% | 1.3 m/s | 3.3 |
| 2018 | 18.2°C | 14.7°C | 11.2°C | 27.0°C | 8.1°C | 85 mm | 80% | 1.4 m/s | 3.7 |
| 2017 | 20.5°C | 16.8°C | 13.0°C | 29.7°C | 9.4°C | 41 mm | 75% | 1.2 m/s | 3.8 |
| 2016 | 18.4°C | 14.8°C | 11.1°C | 22.8°C | 8.0°C | 48 mm | 78% | 1.3 m/s | 4 |
| 2015 | 18.1°C | 14.3°C | 10.6°C | 26.4°C | 7.1°C | 53 mm | 77% | 1.3 m/s | 3.8 |
| 2014 | 21.2°C | 17.2°C | 13.1°C | 27.6°C | 10.6°C | 60 mm | 72% | 1.2 m/s | 4.1 |
| 2013 🌧️ | 19.9°C | 16.4°C | 12.8°C | 28.6°C | 7.6°C | 104 mm | 79% | 1.4 m/s | 3.4 |
| 2012 | 20.8°C | 16.2°C | 11.5°C | 26.8°C | 8.1°C | 17 mm | 72% | 1.1 m/s | 4.6 |
| 2011 | 20.6°C | 16.5°C | 12.4°C | 27.6°C | 7.4°C | 43 mm | 76% | 1.3 m/s | 4 |
| 2010 | 18.5°C | 14.9°C | 11.2°C | 25.5°C | 9.3°C | 92 mm | 81% | 1.3 m/s | 3.4 |
| 2009 | 19.9°C | 15.7°C | 11.5°C | 27.5°C | 5.9°C | 49 mm | 73% | 1.3 m/s | 4.1 |
| 2008 | 19.6°C | 15.4°C | 11.3°C | 24.9°C | 8.7°C | 18 mm | 74% | 1.2 m/s | 4.1 |
| 2007 | 18.4°C | 14.7°C | 11.0°C | 25.8°C | 6.3°C | 46 mm | 78% | 1.3 m/s | 3.7 |
| 2006 | 20.6°C | 16.2°C | 11.8°C | 28.8°C | 8.0°C | 26 mm | 72% | 1.2 m/s | 4.3 |
| 2005 | 18.2°C | 14.6°C | 10.9°C | 21.7°C | 7.1°C | 43 mm | 77% | 1.2 m/s | 4.2 |
| 2004 | 17.8°C | 14.4°C | 11.1°C | 22.0°C | 8.6°C | 77 mm | 81% | 1.3 m/s | 3.6 |
| 2003 | 20.9°C | 16.4°C | 12.0°C | 29.4°C | 9.2°C | 34 mm | 73% | 1.2 m/s | 4.2 |
| 2002 | 19.5°C | 15.3°C | 11.1°C | 25.3°C | 6.7°C | 27 mm | 74% | 1.3 m/s | 4.2 |
| 2001 | 19.0°C | 15.2°C | 11.4°C | 23.7°C | 8.2°C | 35 mm | 79% | 1.2 m/s | 3.9 |
| 2000 | 18.4°C | 15.1°C | 11.8°C | 23.6°C | 7.9°C | 40 mm | 75% | 1.2 m/s | 3.8 |
| 1999 | 19.0°C | 14.9°C | 10.7°C | 25.8°C | 6.6°C | 19 mm | 74% | 1.4 m/s | 4.6 |
| 1998 | 20.8°C | 16.4°C | 12.0°C | 26.2°C | 9.1°C | 14 mm | 76% | 1.2 m/s | 4.5 |
| 1997 | 19.2°C | 15.9°C | 12.7°C | 25.1°C | 10.0°C | 103 mm | 79% | 1.3 m/s | 3.8 |
| 1996 | 17.5°C | 14.0°C | 10.4°C | 24.4°C | 6.8°C | 54 mm | 78% | 1.3 m/s | 3.7 |
| 1995 🔥 | 21.4°C | 17.3°C | 13.2°C | 27.3°C | 9.9°C | 21 mm | 71% | 1.1 m/s | 4.4 |
| 1994 | 20.5°C | 16.5°C | 12.5°C | 24.9°C | 10.4°C | 44 mm | 76% | 1.1 m/s | 4 |
| 1993 | 21.2°C | 16.5°C | 11.8°C | 27.4°C | 7.8°C | 2 mm | 71% | 1 m/s | 4.5 |
| 1992 | 17.8°C | 13.9°C | 10.0°C | 22.0°C | 6.7°C | 25 mm | 74% | 1.5 m/s | 4 |
| 1991 | 20.1°C | 15.9°C | 11.7°C | 25.5°C | 8.9°C | 3 mm | 75% | 1.1 m/s | 4.4 |
| 1990 | 22.0°C | 17.2°C | 12.3°C | 25.5°C | 9.5°C | 14 mm | 71% | 1.1 m/s | 4.2 |
| 1989 | 20.9°C | 16.1°C | 11.4°C | 24.3°C | 8.6°C | 8 mm | 71% | 1.1 m/s | 4.6 |
| 1988 | 19.0°C | 14.8°C | 10.5°C | 29.2°C | 7.1°C | 65 mm | 75% | 1.2 m/s | 3.8 |
| 1987 | 20.8°C | 16.0°C | 11.3°C | 26.3°C | 8.0°C | 16 mm | 72% | 1 m/s | 4.1 |
| 1986 | 17.5°C | 13.8°C | 10.1°C | 22.6°C | 7.3°C | 43 mm | 76% | 1.2 m/s | 3.7 |
| 1985 | 17.3°C | 13.7°C | 10.0°C | 22.0°C | 8.1°C | 41 mm | 74% | 1.3 m/s | 3.9 |
| 1984 ❄️ | 16.8°C | 13.4°C | 10.0°C | 20.6°C | 6.9°C | 53 mm | 76% | 1.3 m/s | 3.6 |
| 1983 | 17.4°C | 13.7°C | 10.0°C | 22.1°C | 5.3°C | 70 mm | 74% | 1.4 m/s | — |
| 1982 | 19.2°C | 15.4°C | 11.6°C | 25.7°C | 8.6°C | 28 mm | 77% | 1.1 m/s | — |
| 1981 | 18.4°C | 14.5°C | 10.7°C | 26.0°C | 5.3°C | 83 mm | 78% | 1.4 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 19.4°C with lows near 11.6°C (mean 15.5°C), based on 45 years of NASA POWER data.
September averages 46 mm of rainfall in Duncan, one of the drier months. The wettest on record was 104 mm in 2013.
The hottest September reached 29.7°C in 2017. The coldest dipped to 5.3°C in 1981.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.8°C. Daytime highs moved from 17.8°C to 19.8°C and overnight lows from 10.5°C to 12.2°C over the same span.
September is one of the warmer months of the year in Duncan and one of the drier months, so plan for around 19.4°C daytime highs and 11.6°C at night.
Not quite — September is the 10th coolest month in Duncan, averaging 15.5°C.
For September in Duncan, pack light layers you can adjust through the day, with typical highs of 19.4°C and lows of 11.6°C.
Relative humidity in September averages 76% — quite humid.
Average wind speed in September is 1.2 m/s. The windiest September on record averaged 1.5 m/s (1992).
The wettest September on record was 2013 with 104 mm. On average, September sees 46 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 Duncan 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.
