September is one of the warmer months of the year in Irvine, with average highs near 28.3°C and lows around 18.1°C (mean 23.2°C). It is one of the drier months, averaging 7 mm of rainfall and 60% relative humidity across the period.
September is one of the warmer months of the year in Irvine. Across 45 years of records, the warmest September in Irvine was 1984 — when the month averaged 26.3°C — while the coldest was 1986 at 19.8°C. Typical September days reach 28.3°C with nights near 18.1°C. The long-term trend is warming, about 0.2°C per decade.
September is one of the drier months in Irvine, averaging 7 mm of rainfall. The wettest September on record was 1983 with 39 mm, while the driest were 1994, 2018 and 2020, among others at 0 mm.
Relative humidity in Irvine during September averages 60%. The most humid September was 2023 at 73%, and the least humid was 2020 at 52%.
September receives about 5.8 kWh/m²/day of solar energy in Irvine. The sunniest September was 2014 at 6.3 kWh/m²/day, and the cloudiest was 2023 at 5.1.
Average wind speed in Irvine during September is 2 m/s. The windiest Septembers were 1986 and 2017 at 2.3 m/s, while the calmest was 2020 at 1.7 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 22.9°C | 23.0°C | 23.0°C | 23.5°C | 23.7°C | +0.8°C |
| Avg High | 28.1°C | 28.0°C | 28.3°C | 28.6°C | 28.5°C | +0.4°C |
| Avg Low | 17.7°C | 17.9°C | 17.8°C | 18.4°C | 18.8°C | +1.1°C |
| Avg Rain | 15 mm | 6 mm | 4 mm | 6 mm | 6 mm | -9 mm |
September temperatures in Irvine have stayed relatively stable across the record.
September has ranged from a record low of 11.2°C (1982) to a record high of 40.1°C (1984).
Rainfall in September is one of the drier months, averaging 7 mm, with a wettest year of 39 mm.
One of the best times to visit Irvine
September is one of the best times to visit Irvine. Expect days averaging 28.3°C and nights around 18.1°C (mean 23.2°C) — warmer than Irvine's yearly average — with low rainfall (7 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 | 28.0°C | 23.5°C | 19.0°C | 32.4°C | 16.7°C | 11 mm | 67% | 2.1 m/s | 5.7 |
| 2024 | 28.1°C | 23.2°C | 18.4°C | 36.7°C | 15.1°C | 2 mm | 61% | 2.1 m/s | 5.8 |
| 2023 | 25.6°C | 21.5°C | 17.4°C | 31.4°C | 14.6°C | 4 mm | 73% | 2.2 m/s | 5.1 |
| 2022 | 30.0°C | 25.3°C | 20.6°C | 35.8°C | 15.0°C | 17 mm | 63% | 2.1 m/s | 5.7 |
| 2021 | 28.3°C | 23.0°C | 17.7°C | 34.1°C | 13.6°C | 3 mm | 60% | 2 m/s | 5.9 |
| 2020 | 31.1°C | 25.4°C | 19.6°C | 38.9°C | 16.1°C | 0 mm | 52% | 1.7 m/s | 5.9 |
| 2019 | 28.3°C | 23.5°C | 18.6°C | 33.0°C | 13.0°C | 3 mm | 62% | 2.2 m/s | 6 |
| 2018 | 28.2°C | 22.7°C | 17.2°C | 32.2°C | 15.1°C | 0 mm | 60% | 2.1 m/s | 6.1 |
| 2017 | 27.8°C | 23.1°C | 18.4°C | 36.7°C | 13.8°C | 3 mm | 65% | 2.3 m/s | 5.7 |
| 2016 | 27.8°C | 22.7°C | 17.6°C | 35.4°C | 14.2°C | 6 mm | 59% | 2 m/s | 5.9 |
| 2015 | 29.7°C | 25.0°C | 20.3°C | 35.2°C | 15.8°C | 31 mm | 64% | 1.9 m/s | 6 |
| 2014 | 29.8°C | 24.9°C | 19.9°C | 36.9°C | 16.1°C | 3 mm | 60% | 2 m/s | 6.3 |
| 2013 | 28.1°C | 23.1°C | 18.1°C | 33.2°C | 13.4°C | 6 mm | 58% | 1.9 m/s | 6.1 |
| 2012 | 30.6°C | 25.2°C | 19.9°C | 38.0°C | 15.4°C | 3 mm | 53% | 1.8 m/s | 6.1 |
| 2011 | 27.7°C | 22.3°C | 16.9°C | 35.4°C | 14.3°C | 5 mm | 59% | 1.8 m/s | 5.5 |
| 2010 | 27.8°C | 22.4°C | 17.0°C | 39.1°C | 13.0°C | 3 mm | 56% | 1.9 m/s | 5.9 |
| 2009 | 30.1°C | 24.5°C | 18.9°C | 37.3°C | 14.3°C | 1 mm | 56% | 2 m/s | 6.2 |
| 2008 | 28.9°C | 23.7°C | 18.4°C | 32.5°C | 15.3°C | 1 mm | 60% | 1.9 m/s | 5.9 |
| 2007 | 26.6°C | 21.8°C | 17.0°C | 35.5°C | 13.0°C | 9 mm | 61% | 2.2 m/s | 6.1 |
| 2006 | 28.3°C | 22.9°C | 17.6°C | 33.1°C | 13.2°C | 3 mm | 55% | 1.9 m/s | 6.1 |
| 2005 | 26.7°C | 21.5°C | 16.4°C | 35.3°C | 12.6°C | 5 mm | 59% | 1.9 m/s | 6.1 |
| 2004 | 28.7°C | 23.5°C | 18.4°C | 35.4°C | 15.3°C | 1 mm | 58% | 2.1 m/s | 6.2 |
| 2003 | 29.0°C | 23.5°C | 18.0°C | 32.8°C | 15.6°C | 2 mm | 62% | 2 m/s | 5.8 |
| 2002 | 28.5°C | 23.3°C | 18.1°C | 35.4°C | 14.4°C | 5 mm | 56% | 1.9 m/s | 5.6 |
| 2001 | 27.9°C | 22.6°C | 17.3°C | 34.4°C | 14.8°C | 2 mm | 61% | 1.9 m/s | 5.9 |
| 2000 | 28.0°C | 22.8°C | 17.6°C | 35.2°C | 14.7°C | 9 mm | 60% | 2 m/s | 5.7 |
| 1999 | 26.6°C | 21.5°C | 16.3°C | 36.3°C | 13.4°C | 4 mm | 63% | 2.1 m/s | 5.7 |
| 1998 | 26.1°C | 21.9°C | 17.7°C | 34.7°C | 14.1°C | 8 mm | 69% | 2.1 m/s | 5.4 |
| 1997 | 30.0°C | 25.0°C | 20.1°C | 34.2°C | 16.2°C | 35 mm | 62% | 1.9 m/s | 5.8 |
| 1996 | 27.2°C | 22.3°C | 17.3°C | 31.0°C | 14.9°C | 1 mm | 65% | 2 m/s | 5.8 |
| 1995 | 28.7°C | 23.6°C | 18.5°C | 32.8°C | 14.6°C | 2 mm | 58% | 2 m/s | 6 |
| 1994 | 27.7°C | 22.6°C | 17.5°C | 31.6°C | 14.3°C | 0 mm | 60% | 1.9 m/s | 5.7 |
| 1993 | 28.0°C | 22.6°C | 17.3°C | 34.9°C | 12.7°C | 0 mm | 56% | 1.9 m/s | 5.6 |
| 1992 | 29.1°C | 23.8°C | 18.5°C | 32.6°C | 15.6°C | 0 mm | 56% | 1.8 m/s | 6 |
| 1991 | 27.7°C | 22.8°C | 17.9°C | 32.1°C | 14.0°C | 7 mm | 63% | 1.8 m/s | 5.5 |
| 1990 | 28.8°C | 23.5°C | 18.3°C | 33.8°C | 15.0°C | 4 mm | 58% | 1.9 m/s | 6 |
| 1989 | 28.4°C | 22.9°C | 17.4°C | 33.7°C | 13.2°C | 11 mm | 54% | 2 m/s | 5.9 |
| 1988 | 28.6°C | 23.0°C | 17.4°C | 40.0°C | 13.4°C | 1 mm | 57% | 2 m/s | 5.3 |
| 1987 | 28.3°C | 22.9°C | 17.6°C | 35.8°C | 14.2°C | 4 mm | 60% | 1.9 m/s | 5.5 |
| 1986 ❄️ | 24.7°C | 19.8°C | 14.9°C | 32.0°C | 12.0°C | 32 mm | 64% | 2.3 m/s | 5.6 |
| 1985 | 26.0°C | 21.2°C | 16.3°C | 30.9°C | 13.9°C | 11 mm | 61% | 2.2 m/s | 5.5 |
| 1984 🔥 | 31.6°C | 26.3°C | 21.0°C | 40.1°C | 16.9°C | 8 mm | 57% | 1.9 m/s | 5.3 |
| 1983 🌧️ | 29.2°C | 24.3°C | 19.4°C | 34.3°C | 14.9°C | 39 mm | 61% | 1.9 m/s | — |
| 1982 | 27.1°C | 22.4°C | 17.7°C | 34.2°C | 11.2°C | 27 mm | 61% | 2 m/s | — |
| 1981 | 28.6°C | 23.1°C | 17.6°C | 32.8°C | 14.1°C | 6 mm | 54% | 1.8 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 28.3°C with lows near 18.1°C (mean 23.2°C), based on 45 years of NASA POWER data.
September averages 7 mm of rainfall in Irvine, one of the drier months. The wettest on record was 39 mm in 1983.
The hottest September reached 40.1°C in 1984. The coldest dipped to 11.2°C in 1982.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have fallen by about 0.2°C — but days and nights have moved in opposite directions. Overnight lows rose from 18.4°C to 18.6°C while daytime highs eased from 28.5°C to 28°C, narrowing the gap between day and night.
September is one of the warmer months of the year in Irvine and one of the drier months, so plan for around 28.3°C daytime highs and 18.1°C at night.
Not quite — September is the 11th coolest month in Irvine, averaging 23.2°C.
For September in Irvine, pack light layers you can adjust through the day, with typical highs of 28.3°C and lows of 18.1°C.
Relative humidity in September averages 60% — moderately humid.
Average wind speed in September is 2 m/s. The windiest September on record averaged 2.3 m/s (1986).
The wettest September on record was 1983 with 39 mm. On average, September sees 7 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 Irvine 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.
