September is one of the warmer months of the year in New Castle, with average highs near 26.1°C and lows around 15.4°C (mean 20.8°C). It is about average for rainfall, averaging 105 mm of rainfall and 73% relative humidity across the period.
September is one of the warmer months of the year in New Castle. Across 45 years of records, the warmest September in New Castle was 2005 — when the month averaged 23.2°C — while the coldest was 2000 at 18.6°C. Typical September days reach 26.1°C with nights near 15.4°C. The long-term trend is warming, about 0.5°C per decade.
September is about average for rainfall in New Castle, averaging 105 mm of rainfall. The wettest September on record was 1999 with 287 mm, while the driest were 2005 and 2019 at 15 mm.
Relative humidity in New Castle during September averages 73%. The most humid September was 2011 at 87%, and the least humid was 1983 at 63%.
September receives about 4.4 kWh/m²/day of solar energy in New Castle. The sunniest September was 2007 at 5.2 kWh/m²/day, and the cloudiest was 2018 at 3.5.
Average wind speed in New Castle during September is 2.3 m/s. The windiest September was 1999 at 2.7 m/s, while the calmest were 1982, 2011 and 2013 at 2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 20.0°C | 20.2°C | 20.6°C | 21.6°C | 21.5°C | +1.5°C |
| Avg High | 25.7°C | 25.5°C | 25.9°C | 26.8°C | 26.8°C | +1.1°C |
| Avg Low | 14.4°C | 14.8°C | 15.3°C | 16.4°C | 16.3°C | +1.9°C |
| Avg Rain | 95 mm | 115 mm | 107 mm | 104 mm | 100 mm | +5 mm |
September temperatures in New Castle have risen by about 1.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 4.5°C (1992) to a record high of 36.3°C (1983).
Rainfall in September is about average for rainfall, averaging 105 mm, with a wettest year of 287 mm.
One of the best times to visit New Castle
September is one of the best times to visit New Castle. Expect days averaging 26.1°C and nights around 15.4°C (mean 20.8°C) — warmer than New Castle's yearly average — with higher rainfall (105 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 | 27.9°C | 22.3°C | 16.7°C | 33.0°C | 11.9°C | 80 mm | 71% | 2.2 m/s | 4.4 |
| 2024 | 27.2°C | 21.9°C | 16.6°C | 30.4°C | 11.3°C | 25 mm | 73% | 2.4 m/s | 4.2 |
| 2023 | 26.9°C | 21.8°C | 16.7°C | 36.3°C | 11.6°C | 165 mm | 75% | 2.3 m/s | 4.2 |
| 2022 | 26.9°C | 21.4°C | 15.8°C | 32.0°C | 8.5°C | 90 mm | 70% | 2.4 m/s | 4.7 |
| 2021 | 26.4°C | 21.5°C | 16.7°C | 30.7°C | 11.0°C | 134 mm | 79% | 2.4 m/s | 4.6 |
| 2020 | 25.3°C | 20.2°C | 15.2°C | 30.9°C | 6.0°C | 105 mm | 77% | 2.1 m/s | 4.3 |
| 2019 | 29.1°C | 23.1°C | 17.1°C | 33.9°C | 10.5°C | 15 mm | 67% | 2.2 m/s | 4.7 |
| 2018 | 26.4°C | 22.5°C | 18.6°C | 33.8°C | 12.1°C | 175 mm | 85% | 2.3 m/s | 3.5 |
| 2017 | 26.1°C | 21.0°C | 15.8°C | 31.9°C | 9.6°C | 54 mm | 74% | 2.2 m/s | 4.5 |
| 2016 | 28.3°C | 22.8°C | 17.3°C | 35.5°C | 10.3°C | 133 mm | 68% | 2.4 m/s | 4.3 |
| 2015 | 28.4°C | 22.7°C | 17.0°C | 34.6°C | 12.1°C | 99 mm | 70% | 2.2 m/s | 4.5 |
| 2014 | 26.1°C | 20.9°C | 15.7°C | 32.7°C | 9.1°C | 70 mm | 73% | 2.1 m/s | 4.5 |
| 2013 | 25.3°C | 19.3°C | 13.4°C | 33.6°C | 6.1°C | 39 mm | 71% | 2 m/s | 5.1 |
| 2012 | 25.5°C | 20.5°C | 15.6°C | 33.6°C | 8.3°C | 103 mm | 74% | 2.2 m/s | 4.6 |
| 2011 | 24.8°C | 20.8°C | 16.8°C | 28.3°C | 7.5°C | 202 mm | 87% | 2 m/s | 3.6 |
| 2010 | 28.3°C | 22.3°C | 16.4°C | 35.3°C | 10.1°C | 152 mm | 66% | 2.5 m/s | 4.7 |
| 2009 | 23.2°C | 18.9°C | 14.7°C | 27.8°C | 10.1°C | 126 mm | 82% | 2.3 m/s | 4.1 |
| 2008 | 26.7°C | 21.3°C | 16.0°C | 34.6°C | 10.1°C | 137 mm | 74% | 2.3 m/s | 4.3 |
| 2007 | 28.2°C | 22.2°C | 16.1°C | 33.2°C | 9.3°C | 25 mm | 68% | 2.1 m/s | 5.2 |
| 2006 | 24.2°C | 19.4°C | 14.7°C | 29.2°C | 8.7°C | 132 mm | 78% | 2.4 m/s | 3.9 |
| 2005 🔥 | 29.3°C | 23.2°C | 17.0°C | 33.0°C | 8.2°C | 15 mm | 65% | 2.1 m/s | 5.1 |
| 2004 | 26.4°C | 21.3°C | 16.2°C | 29.7°C | 8.6°C | 138 mm | 79% | 2.3 m/s | 4.1 |
| 2003 | 24.5°C | 20.1°C | 15.7°C | 27.8°C | 7.2°C | 178 mm | 84% | 2.6 m/s | 4.2 |
| 2002 | 27.1°C | 21.4°C | 15.8°C | 31.9°C | 11.3°C | 108 mm | 71% | 2.4 m/s | 4.8 |
| 2001 | 25.4°C | 19.5°C | 13.7°C | 29.8°C | 7.5°C | 69 mm | 70% | 2.3 m/s | 4.6 |
| 2000 ❄️ | 24.0°C | 18.6°C | 13.2°C | 29.5°C | 5.8°C | 145 mm | 78% | 2.3 m/s | 4.4 |
| 1999 🌧️ | 24.9°C | 20.1°C | 15.2°C | 30.6°C | 7.4°C | 287 mm | 79% | 2.7 m/s | 4.2 |
| 1998 | 28.5°C | 22.4°C | 16.3°C | 33.6°C | 7.3°C | 53 mm | 65% | 2.3 m/s | 4.8 |
| 1997 | 25.3°C | 19.8°C | 14.3°C | 31.2°C | 6.6°C | 58 mm | 69% | 2.5 m/s | 4.4 |
| 1996 | 24.8°C | 20.1°C | 15.3°C | 30.8°C | 9.3°C | 135 mm | 80% | 2.6 m/s | 4 |
| 1995 | 26.2°C | 20.3°C | 14.4°C | 32.8°C | 7.3°C | 102 mm | 66% | 2.2 m/s | 4.5 |
| 1994 | 24.5°C | 19.0°C | 13.6°C | 30.9°C | 8.3°C | 81 mm | 72% | 2.3 m/s | 4.6 |
| 1993 | 25.5°C | 20.6°C | 15.7°C | 34.1°C | 5.2°C | 138 mm | 73% | 2.4 m/s | 3.7 |
| 1992 | 24.6°C | 19.7°C | 14.7°C | 29.7°C | 4.5°C | 123 mm | 76% | 2.5 m/s | 4 |
| 1991 | 25.6°C | 20.2°C | 14.7°C | 33.7°C | 5.2°C | 112 mm | 68% | 2.3 m/s | 4.6 |
| 1990 | 25.0°C | 19.5°C | 13.9°C | 32.7°C | 5.0°C | 58 mm | 72% | 2.2 m/s | 4.4 |
| 1989 | 24.3°C | 19.7°C | 15.0°C | 31.7°C | 6.0°C | 143 mm | 81% | 2.4 m/s | 4.2 |
| 1988 | 24.7°C | 18.9°C | 13.2°C | 29.9°C | 8.2°C | 70 mm | 72% | 2.1 m/s | 4.5 |
| 1987 | 25.5°C | 20.5°C | 15.5°C | 29.2°C | 9.4°C | 140 mm | 77% | 2.1 m/s | 4.2 |
| 1986 | 26.1°C | 20.4°C | 14.8°C | 31.8°C | 5.9°C | 44 mm | 70% | 2.2 m/s | 4.3 |
| 1985 | 26.5°C | 20.9°C | 15.2°C | 33.5°C | 7.4°C | 160 mm | 69% | 2.1 m/s | 4.6 |
| 1984 | 24.8°C | 18.8°C | 12.8°C | 32.0°C | 6.1°C | 57 mm | 70% | 2.2 m/s | 4.9 |
| 1983 | 27.6°C | 21.2°C | 14.7°C | 36.3°C | 6.3°C | 77 mm | 63% | 2.2 m/s | — |
| 1982 | 26.1°C | 20.3°C | 14.5°C | 31.2°C | 9.7°C | 66 mm | 69% | 2 m/s | — |
| 1981 | 25.4°C | 19.6°C | 13.8°C | 32.4°C | 5.8°C | 98 mm | 69% | 2.4 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 26.1°C with lows near 15.4°C (mean 20.8°C), based on 45 years of NASA POWER data.
September averages 105 mm of rainfall in New Castle, about average for rainfall. The wettest on record was 287 mm in 1999.
The hottest September reached 36.3°C in 1983. The coldest dipped to 4.5°C in 1992.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.6°C. Daytime highs moved from 26.1°C to 27.1°C and overnight lows from 14.2°C to 16.5°C over the same span.
September is one of the warmer months of the year in New Castle and about average for rainfall, so plan for around 26.1°C daytime highs and 15.4°C at night.
Not quite — September is the 9th coolest month in New Castle, averaging 20.8°C.
For September in New Castle, pack light layers you can adjust through the day, with typical highs of 26.1°C and lows of 15.4°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 73% — moderately humid.
Average wind speed in September is 2.3 m/s. The windiest September on record averaged 2.7 m/s (1999).
The wettest September on record was 1999 with 287 mm. On average, September sees 105 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 New Castle 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.
