September is one of the warmer months of the year in Whittier, with average highs near 29.6°C and lows around 17.6°C (mean 23.6°C). It is one of the drier months, averaging 6 mm of rainfall and 51% relative humidity across the period.
September is one of the warmer months of the year in Whittier. Across 45 years of records, the warmest September in Whittier was 1984 — when the month averaged 26.6°C — while the coldest was 1986 at 19.7°C. Typical September days reach 29.6°C with nights near 17.6°C. The long-term trend is warming, about 0.2°C per decade.
September is one of the drier months in Whittier, averaging 6 mm of rainfall. The wettest September on record was 1983 with 52 mm, while the driest were 2009, 2018 and 2020, among others at 0 mm.
Relative humidity in Whittier during September averages 51%. The most humid September was 2023 at 69%, and the least humid was 2020 at 42%.
September receives about 5.4 kWh/m²/day of solar energy in Whittier. The sunniest September was 2014 at 6 kWh/m²/day, and the cloudiest was 1991 at 4.5.
Average wind speed in Whittier during September is 1.8 m/s. The windiest Septembers were 1985 and 1986 at 2.1 m/s, while the calmest were 1991 and 2020 at 1.5 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 23.1°C | 23.4°C | 23.5°C | 23.9°C | 24.1°C | +1°C |
| Avg High | 29.2°C | 29.4°C | 29.8°C | 29.9°C | 29.9°C | +0.7°C |
| Avg Low | 17.1°C | 17.5°C | 17.3°C | 17.9°C | 18.4°C | +1.3°C |
| Avg Rain | 16 mm | 3 mm | 3 mm | 4 mm | 5 mm | -12 mm |
September temperatures in Whittier have stayed relatively stable across the record.
September has ranged from a record low of 9°C (1982) to a record high of 41.5°C (2020).
Rainfall in September is one of the drier months, averaging 6 mm, with a wettest year of 52 mm.
One of the best times to visit Whittier
September is one of the best times to visit Whittier. Expect days averaging 29.6°C and nights around 17.6°C (mean 23.6°C) — warmer than Whittier's yearly average — with low rainfall (6 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 | 29.1°C | 23.8°C | 18.6°C | 35.2°C | 16.1°C | 7 mm | 62% | 1.8 m/s | 5.3 |
| 2024 | 30.1°C | 24.2°C | 18.3°C | 40.0°C | 13.4°C | 1 mm | 51% | 1.8 m/s | 5.3 |
| 2023 | 26.8°C | 21.8°C | 16.8°C | 32.4°C | 13.8°C | 4 mm | 69% | 1.9 m/s | 5 |
| 2022 | 31.4°C | 25.7°C | 20.1°C | 38.1°C | 15.0°C | 14 mm | 55% | 1.9 m/s | 5.7 |
| 2021 | 29.5°C | 23.4°C | 17.4°C | 35.2°C | 12.5°C | 1 mm | 50% | 1.6 m/s | 5.5 |
| 2020 | 32.3°C | 25.8°C | 19.2°C | 41.5°C | 14.8°C | 0 mm | 42% | 1.5 m/s | 5.5 |
| 2019 | 29.7°C | 23.8°C | 17.9°C | 35.5°C | 11.1°C | 1 mm | 53% | 1.8 m/s | 5.8 |
| 2018 | 29.4°C | 23.2°C | 17.0°C | 33.6°C | 14.2°C | 0 mm | 52% | 1.7 m/s | 5.3 |
| 2017 | 28.9°C | 23.2°C | 17.5°C | 39.9°C | 12.1°C | 4 mm | 57% | 2 m/s | 5.7 |
| 2016 | 29.2°C | 23.0°C | 16.8°C | 36.6°C | 13.0°C | 1 mm | 50% | 1.8 m/s | 5.6 |
| 2015 | 30.6°C | 25.0°C | 19.5°C | 37.0°C | 14.7°C | 29 mm | 56% | 1.7 m/s | 5.8 |
| 2014 | 30.9°C | 25.0°C | 19.1°C | 38.3°C | 14.2°C | 1 mm | 51% | 1.7 m/s | 6 |
| 2013 | 29.8°C | 23.6°C | 17.5°C | 36.2°C | 11.4°C | 1 mm | 47% | 1.8 m/s | 5.8 |
| 2012 | 31.5°C | 25.5°C | 19.6°C | 37.4°C | 14.8°C | 1 mm | 43% | 1.7 m/s | 5.7 |
| 2011 | 29.3°C | 23.2°C | 17.1°C | 37.0°C | 13.6°C | 2 mm | 49% | 1.6 m/s | 4.7 |
| 2010 | 29.7°C | 23.2°C | 16.7°C | 40.2°C | 11.3°C | 1 mm | 45% | 1.7 m/s | 5.2 |
| 2009 | 31.3°C | 24.9°C | 18.5°C | 37.1°C | 11.3°C | 0 mm | 48% | 1.7 m/s | 5.4 |
| 2008 | 30.5°C | 24.3°C | 18.1°C | 34.7°C | 13.9°C | 0 mm | 51% | 1.8 m/s | 5 |
| 2007 | 27.9°C | 22.1°C | 16.3°C | 39.2°C | 12.1°C | 14 mm | 55% | 1.9 m/s | 5.9 |
| 2006 | 29.6°C | 23.3°C | 17.0°C | 35.8°C | 11.1°C | 1 mm | 45% | 1.7 m/s | 5.6 |
| 2005 | 27.8°C | 21.7°C | 15.7°C | 35.2°C | 11.4°C | 6 mm | 52% | 1.7 m/s | 5.7 |
| 2004 | 30.2°C | 23.9°C | 17.5°C | 35.6°C | 12.2°C | 0 mm | 50% | 1.9 m/s | 5.8 |
| 2003 | 30.7°C | 24.2°C | 17.8°C | 34.5°C | 14.6°C | 0 mm | 51% | 1.6 m/s | 4.8 |
| 2002 | 30.2°C | 24.0°C | 17.8°C | 37.7°C | 13.6°C | 1 mm | 46% | 1.8 m/s | 5.2 |
| 2001 | 29.7°C | 23.5°C | 17.3°C | 35.2°C | 14.1°C | 1 mm | 52% | 1.6 m/s | 4.9 |
| 2000 | 29.6°C | 23.3°C | 17.1°C | 37.6°C | 13.8°C | 5 mm | 51% | 1.9 m/s | 5.5 |
| 1999 | 28.4°C | 22.3°C | 16.2°C | 36.6°C | 12.9°C | 1 mm | 54% | 1.7 m/s | 4.7 |
| 1998 | 27.5°C | 22.3°C | 17.1°C | 37.1°C | 13.2°C | 10 mm | 62% | 1.9 m/s | 5.2 |
| 1997 | 31.2°C | 25.3°C | 19.5°C | 35.1°C | 15.6°C | 16 mm | 51% | 1.8 m/s | 5.7 |
| 1996 | 28.3°C | 22.4°C | 16.5°C | 32.3°C | 13.5°C | 0 mm | 57% | 1.8 m/s | 5.2 |
| 1995 | 30.3°C | 24.3°C | 18.3°C | 34.3°C | 11.7°C | 0 mm | 47% | 1.8 m/s | 5.6 |
| 1994 | 28.9°C | 23.0°C | 17.1°C | 32.9°C | 12.8°C | 1 mm | 51% | 1.8 m/s | 5.7 |
| 1993 | 29.5°C | 23.1°C | 16.7°C | 36.3°C | 10.6°C | 0 mm | 46% | 1.8 m/s | 5.2 |
| 1992 | 30.6°C | 24.4°C | 18.1°C | 34.8°C | 13.4°C | 0 mm | 46% | 1.7 m/s | 5.4 |
| 1991 | 29.1°C | 23.4°C | 17.7°C | 34.5°C | 12.8°C | 2 mm | 53% | 1.5 m/s | 4.5 |
| 1990 | 30.1°C | 23.8°C | 17.6°C | 36.5°C | 13.8°C | 1 mm | 48% | 1.8 m/s | 5.7 |
| 1989 | 29.6°C | 23.2°C | 16.7°C | 34.5°C | 11.6°C | 12 mm | 44% | 1.9 m/s | 5.5 |
| 1988 | 29.9°C | 23.4°C | 16.9°C | 40.5°C | 12.5°C | 2 mm | 48% | 1.8 m/s | 4.6 |
| 1987 | 29.7°C | 23.4°C | 17.1°C | 37.7°C | 13.4°C | 3 mm | 51% | 1.8 m/s | 5 |
| 1986 ❄️ | 25.7°C | 19.7°C | 13.7°C | 33.4°C | 9.9°C | 34 mm | 56% | 2.1 m/s | 5 |
| 1985 | 26.7°C | 21.0°C | 15.3°C | 32.5°C | 12.0°C | 5 mm | 55% | 2.1 m/s | 5.4 |
| 1984 🔥 | 32.5°C | 26.6°C | 20.7°C | 38.7°C | 15.6°C | 7 mm | 48% | 2 m/s | 5.4 |
| 1983 🌧️ | 30.3°C | 24.6°C | 18.9°C | 36.4°C | 14.1°C | 52 mm | 52% | 1.8 m/s | — |
| 1982 | 28.2°C | 22.6°C | 16.9°C | 39.2°C | 9.0°C | 24 mm | 51% | 1.9 m/s | — |
| 1981 | 29.9°C | 23.6°C | 17.4°C | 35.7°C | 13.0°C | 7 mm | 43% | 1.7 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 29.6°C with lows near 17.6°C (mean 23.6°C), based on 45 years of NASA POWER data.
September averages 6 mm of rainfall in Whittier, one of the drier months. The wettest on record was 52 mm in 1983.
The hottest September reached 41.5°C in 2020. The coldest dipped to 9°C in 1982.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 0.1°C — but days and nights have moved in opposite directions. Overnight lows rose from 17.8°C to 18.2°C while daytime highs eased from 29.5°C to 29.4°C, narrowing the gap between day and night.
September is one of the warmer months of the year in Whittier and one of the drier months, so plan for around 29.6°C daytime highs and 17.6°C at night.
Not quite — September is the 10th coolest month in Whittier, averaging 23.6°C.
For September in Whittier, pack light layers you can adjust through the day, with typical highs of 29.6°C and lows of 17.6°C.
Relative humidity in September averages 51% — relatively dry.
Average wind speed in September is 1.8 m/s. The windiest September on record averaged 2.1 m/s (1985).
The wettest September on record was 1983 with 52 mm. On average, September sees 6 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 Whittier 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.
