September is one of the warmer months of the year in New Castle, with average highs near 24.9°C and lows around 11.7°C (mean 18.3°C). It is about average for rainfall, averaging 84 mm of rainfall and 71% 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 2016 — when the month averaged 21.1°C — while the coldest was 2006 at 16.2°C. Typical September days reach 24.9°C with nights near 11.7°C. The long-term trend is warming, about 0.6°C per decade.
September is about average for rainfall in New Castle, averaging 84 mm of rainfall. The wettest September on record was 2004 with 177 mm, while the driest was 2023 at 28 mm.
Relative humidity in New Castle during September averages 71%. The most humid September was 2018 at 81%, and the least humid was 1999 at 62%.
September receives about 4.1 kWh/m²/day of solar energy in New Castle. The sunniest Septembers were 2005, 2007 and 2025 at 4.7 kWh/m²/day, and the cloudiest was 1993 at 3.2.
Average wind speed in New Castle during September is 0.1 m/s. The windiest Septembers were 2022, 2023 and 2025, among others at 0.1 m/s, while the calmest were 2018, 2021 and 2024, among others at 0 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 17.6°C | 17.5°C | 18.2°C | 19.3°C | 19.3°C | +1.7°C |
| Avg High | 24.2°C | 24.0°C | 24.9°C | 25.8°C | 26.1°C | +1.9°C |
| Avg Low | 10.9°C | 10.9°C | 11.6°C | 12.8°C | 12.5°C | +1.6°C |
| Avg Rain | 85 mm | 89 mm | 90 mm | 85 mm | 62 mm | -22 mm |
September temperatures in New Castle have risen by about 2.1°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 0.5°C (1995) to a record high of 36.4°C (2011).
Rainfall in September is about average for rainfall, averaging 84 mm, with a wettest year of 177 mm.
One of the best times to visit New Castle
September is one of the best times to visit New Castle. Expect days averaging 24.9°C and nights around 11.7°C (mean 18.3°C) — warmer than New Castle's yearly average — with higher rainfall (84 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 | 20.1°C | 12.4°C | 31.1°C | 6.8°C | 61 mm | 63% | 0.1 m/s | 4.7 |
| 2024 | 27.3°C | 20.4°C | 13.5°C | 32.2°C | 6.9°C | 79 mm | 67% | 0 m/s | 4.4 |
| 2023 | 25.9°C | 19.2°C | 12.5°C | 34.5°C | 6.2°C | 28 mm | 72% | 0.1 m/s | 4.3 |
| 2022 | 24.9°C | 18.7°C | 12.5°C | 32.1°C | 3.5°C | 78 mm | 73% | 0.1 m/s | 3.9 |
| 2021 | 25.9°C | 19.3°C | 12.6°C | 31.1°C | 6.7°C | 50 mm | 70% | 0 m/s | 4.5 |
| 2020 | 24.8°C | 18.1°C | 11.4°C | 31.2°C | 2.6°C | 79 mm | 72% | 0.1 m/s | 4.4 |
| 2019 | 27.4°C | 20.7°C | 14.0°C | 31.7°C | 8.1°C | 77 mm | 72% | 0.1 m/s | 4.4 |
| 2018 | 26.0°C | 20.5°C | 15.0°C | 36.1°C | 6.7°C | 167 mm | 81% | 0 m/s | 3.8 |
| 2017 | 26.5°C | 19.6°C | 12.7°C | 34.1°C | 5.0°C | 30 mm | 67% | 0.1 m/s | 4.4 |
| 2016 🔥 | 28.3°C | 21.1°C | 14.0°C | 33.6°C | 8.5°C | 101 mm | 67% | 0.1 m/s | 4.6 |
| 2015 | 27.8°C | 20.9°C | 14.1°C | 34.2°C | 8.3°C | 85 mm | 67% | 0.1 m/s | 4.4 |
| 2014 | 24.9°C | 18.0°C | 11.2°C | 31.7°C | 5.0°C | 39 mm | 71% | 0.1 m/s | 4.3 |
| 2013 | 24.3°C | 17.6°C | 10.8°C | 33.9°C | 3.7°C | 53 mm | 71% | 0 m/s | 4.1 |
| 2012 | 23.7°C | 17.3°C | 11.0°C | 31.3°C | 4.5°C | 111 mm | 73% | 0.1 m/s | 4 |
| 2011 | 23.7°C | 18.3°C | 12.9°C | 36.4°C | 4.3°C | 131 mm | 80% | 0.1 m/s | 3.4 |
| 2010 | 25.2°C | 18.7°C | 12.1°C | 34.4°C | 8.4°C | 60 mm | 65% | 0 m/s | 3.9 |
| 2009 | 23.9°C | 17.8°C | 11.8°C | 28.6°C | 3.1°C | 55 mm | 73% | 0 m/s | 4.1 |
| 2008 | 25.9°C | 19.0°C | 12.1°C | 33.7°C | 8.2°C | 71 mm | 69% | 0.1 m/s | 4.2 |
| 2007 | 26.6°C | 19.4°C | 12.1°C | 33.7°C | 4.4°C | 57 mm | 69% | 0.1 m/s | 4.7 |
| 2006 ❄️ | 21.5°C | 16.2°C | 11.0°C | 28.8°C | 4.5°C | 128 mm | 79% | 0.1 m/s | 3.3 |
| 2005 | 27.1°C | 19.9°C | 12.7°C | 32.6°C | 3.9°C | 67 mm | 67% | 0.1 m/s | 4.7 |
| 2004 🌧️ | 24.5°C | 18.3°C | 12.1°C | 29.0°C | 5.4°C | 177 mm | 79% | 0.1 m/s | 4.4 |
| 2003 | 22.3°C | 16.6°C | 10.9°C | 27.7°C | 4.7°C | 145 mm | 80% | 0.1 m/s | 3.8 |
| 2002 | 27.9°C | 20.4°C | 13.0°C | 35.2°C | 7.4°C | 79 mm | 63% | 0.1 m/s | 4.6 |
| 2001 | 24.3°C | 17.1°C | 9.9°C | 32.9°C | 4.4°C | 49 mm | 66% | 0 m/s | 4.4 |
| 2000 | 24.5°C | 17.5°C | 10.6°C | 32.8°C | 0.6°C | 75 mm | 69% | 0 m/s | 4.2 |
| 1999 | 26.0°C | 18.5°C | 11.0°C | 34.4°C | 1.9°C | 65 mm | 62% | 0.1 m/s | 4.4 |
| 1998 | 27.2°C | 19.9°C | 12.6°C | 35.0°C | 5.4°C | 38 mm | 65% | 0.1 m/s | 4.3 |
| 1997 | 23.5°C | 17.1°C | 10.7°C | 30.4°C | 3.3°C | 95 mm | 73% | 0.1 m/s | 4.1 |
| 1996 | 22.9°C | 17.5°C | 12.1°C | 31.3°C | 6.7°C | 159 mm | 79% | 0.1 m/s | 3.5 |
| 1995 | 24.1°C | 16.9°C | 9.7°C | 31.3°C | 0.5°C | 38 mm | 66% | 0.1 m/s | 4.4 |
| 1994 | 23.5°C | 16.8°C | 10.2°C | 30.2°C | 5.3°C | 70 mm | 70% | 0.1 m/s | 4.3 |
| 1993 | 22.6°C | 16.5°C | 10.5°C | 31.6°C | 2.4°C | 100 mm | 71% | 0.1 m/s | 3.2 |
| 1992 | 23.1°C | 16.7°C | 10.3°C | 28.5°C | 1.3°C | 103 mm | 77% | 0.1 m/s | 3.9 |
| 1991 | 25.0°C | 17.9°C | 10.8°C | 33.0°C | 2.1°C | 72 mm | 63% | 0.1 m/s | 4.4 |
| 1990 | 22.5°C | 16.8°C | 11.2°C | 29.9°C | 3.7°C | 155 mm | 80% | 0.1 m/s | 3.6 |
| 1989 | 24.1°C | 17.6°C | 11.0°C | 31.0°C | 0.7°C | 115 mm | 74% | 0 m/s | 4 |
| 1988 | 24.0°C | 17.1°C | 10.1°C | 29.6°C | 4.5°C | 69 mm | 72% | 0.1 m/s | 4.1 |
| 1987 | 23.3°C | 17.3°C | 11.3°C | 27.2°C | 3.3°C | 98 mm | 78% | 0.1 m/s | 3.5 |
| 1986 | 25.7°C | 19.2°C | 12.6°C | 29.3°C | 2.5°C | 111 mm | 70% | 0.1 m/s | 3.8 |
| 1985 | 26.0°C | 18.7°C | 11.5°C | 32.0°C | 3.4°C | 38 mm | 64% | 0.1 m/s | 4.3 |
| 1984 | 23.0°C | 16.3°C | 9.6°C | 31.7°C | 2.4°C | 54 mm | 71% | 0.1 m/s | 3.8 |
| 1983 | 25.4°C | 18.3°C | 11.1°C | 33.9°C | 1.9°C | 78 mm | 65% | 0.1 m/s | — |
| 1982 | 24.1°C | 17.3°C | 10.5°C | 32.1°C | 4.5°C | 86 mm | 71% | 0.1 m/s | — |
| 1981 | 22.1°C | 16.5°C | 10.8°C | 29.8°C | 2.1°C | 111 mm | 76% | 0.1 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 24.9°C with lows near 11.7°C (mean 18.3°C), based on 45 years of NASA POWER data.
September averages 84 mm of rainfall in New Castle, about average for rainfall. The wettest on record was 177 mm in 2004.
The hottest September reached 36.4°C in 2011. The coldest dipped to 0.5°C in 1995.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 2.1°C. Daytime highs moved from 24.1°C to 26.4°C and overnight lows from 10.7°C to 12.7°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 24.9°C daytime highs and 11.7°C at night.
Not quite — September is the 9th coolest month in New Castle, averaging 18.3°C.
For September in New Castle, pack light layers you can adjust through the day, with typical highs of 24.9°C and lows of 11.7°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 71% — moderately humid.
Average wind speed in September is 0.1 m/s. The windiest September on record averaged 0.1 m/s (1981).
The wettest September on record was 2004 with 177 mm. On average, September sees 84 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.
