September is one of the warmer months of the year in Kailua, with average highs near 26.8°C and lows around 25.3°C (mean 26.1°C). It is one of the drier months, averaging 34 mm of rainfall and 77% relative humidity across the period.
September is one of the warmer months of the year in Kailua. Across 45 years of records, the warmest September in Kailua was 2019 — when the month averaged 27.6°C — while the coldest was 1983 at 24.8°C. Typical September days reach 26.8°C with nights near 25.3°C. The long-term trend is warming, about 0.3°C per decade.
September is one of the drier months in Kailua, averaging 34 mm of rainfall. The wettest September on record was 1982 with 170 mm, while the driest was 2010 at 4 mm.
Relative humidity in Kailua during September averages 77%. The most humid September was 1992 at 81%, and the least humid was 1995 at 73%.
September receives about 6.1 kWh/m²/day of solar energy in Kailua. The sunniest Septembers were 2020, 2022 and 2024, among others at 6.5 kWh/m²/day, and the cloudiest was 1986 at 5.4.
Average wind speed in Kailua during September is 5.8 m/s. The windiest September was 2005 at 7.1 m/s, while the calmest was 2014 at 4.4 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 25.6°C | 25.8°C | 26.1°C | 26.4°C | 26.6°C | +1°C |
| Avg High | 26.3°C | 26.5°C | 26.7°C | 27.2°C | 27.4°C | +1.1°C |
| Avg Low | 24.9°C | 25.1°C | 25.4°C | 25.7°C | 25.7°C | +0.8°C |
| Avg Rain | 54 mm | 18 mm | 27 mm | 46 mm | 21 mm | -33 mm |
September temperatures in Kailua have risen by about 1.2°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 23.1°C (1983) to a record high of 29.4°C (2015).
Rainfall in September is one of the drier months, averaging 34 mm, with a wettest year of 170 mm.
A quieter season to visit Kailua
If your dates are flexible, the more temperate months of February and April tend to be the most comfortable for visiting Kailua. That said, September — with days averaging 26.8°C and nights around 25.3°C (mean 26.1°C) and moderate rainfall (34 mm) — can still be rewarding for travellers who don't mind the warmth, and often means fewer crowds.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 27.8°C | 26.9°C | 26.0°C | 28.4°C | 25.3°C | 10 mm | 75% | 5.5 m/s | 6.4 |
| 2024 | 27.6°C | 26.8°C | 25.9°C | 28.4°C | 25.3°C | 8 mm | 75% | 5.7 m/s | 6.5 |
| 2023 | 27.4°C | 26.5°C | 25.7°C | 27.9°C | 25.1°C | 8 mm | 76% | 6.4 m/s | 6.4 |
| 2022 | 27.7°C | 26.9°C | 26.0°C | 28.6°C | 25.5°C | 32 mm | 76% | 5.4 m/s | 6.5 |
| 2021 | 26.6°C | 25.8°C | 25.1°C | 27.3°C | 24.6°C | 47 mm | 78% | 6.7 m/s | 6.3 |
| 2020 | 27.3°C | 26.5°C | 25.7°C | 27.7°C | 25.2°C | 19 mm | 76% | 5.9 m/s | 6.5 |
| 2019 🔥 | 28.3°C | 27.6°C | 26.9°C | 29.2°C | 26.4°C | 73 mm | 78% | 5.9 m/s | 6.1 |
| 2018 | 27.3°C | 26.5°C | 25.8°C | 28.4°C | 24.4°C | 102 mm | 80% | 5 m/s | 6 |
| 2017 | 27.7°C | 26.8°C | 25.9°C | 28.8°C | 25.0°C | 19 mm | 74% | 4.6 m/s | 6.4 |
| 2016 | 26.9°C | 26.3°C | 25.7°C | 27.8°C | 25.0°C | 71 mm | 80% | 6.4 m/s | 5.9 |
| 2015 | 28.0°C | 27.3°C | 26.6°C | 29.4°C | 25.5°C | 95 mm | 78% | 5.7 m/s | 5.7 |
| 2014 | 28.0°C | 27.1°C | 26.2°C | 29.1°C | 25.4°C | 38 mm | 77% | 4.4 m/s | 6.4 |
| 2013 | 27.1°C | 26.3°C | 25.6°C | 28.0°C | 25.1°C | 26 mm | 76% | 6.1 m/s | 6.2 |
| 2012 | 25.9°C | 25.2°C | 24.4°C | 26.7°C | 24.0°C | 29 mm | 77% | 6.4 m/s | 6.2 |
| 2011 | 26.3°C | 25.6°C | 24.8°C | 27.2°C | 24.1°C | 7 mm | 76% | 5.4 m/s | 6.4 |
| 2010 | 26.3°C | 25.5°C | 24.6°C | 27.1°C | 24.2°C | 4 mm | 76% | 5.6 m/s | 6.4 |
| 2009 | 26.7°C | 26.1°C | 25.4°C | 27.2°C | 24.6°C | 17 mm | 76% | 6.3 m/s | 6.4 |
| 2008 | 26.5°C | 25.8°C | 25.0°C | 27.6°C | 24.4°C | 23 mm | 75% | 5.3 m/s | 6.3 |
| 2007 | 26.7°C | 26.0°C | 25.4°C | 27.6°C | 24.5°C | 26 mm | 76% | 6.6 m/s | 6.1 |
| 2006 | 26.6°C | 26.0°C | 25.3°C | 27.1°C | 24.9°C | 30 mm | 76% | 6.2 m/s | 6.3 |
| 2005 | 27.0°C | 26.3°C | 25.7°C | 28.1°C | 24.8°C | 45 mm | 78% | 7.1 m/s | 6.1 |
| 2004 | 27.7°C | 27.0°C | 26.3°C | 28.5°C | 25.6°C | 29 mm | 75% | 6.1 m/s | 6.3 |
| 2003 | 27.2°C | 26.4°C | 25.7°C | 28.2°C | 25.3°C | 28 mm | 74% | 5.3 m/s | 6.4 |
| 2002 | 26.7°C | 26.0°C | 25.2°C | 28.2°C | 24.7°C | 20 mm | 75% | 5.5 m/s | 6.2 |
| 2001 | 26.3°C | 25.7°C | 25.1°C | 27.0°C | 24.3°C | 27 mm | 76% | 6.4 m/s | 6.1 |
| 2000 | 26.0°C | 25.3°C | 24.7°C | 27.5°C | 23.7°C | 22 mm | 79% | 5.8 m/s | 5.9 |
| 1999 | 25.8°C | 25.1°C | 24.4°C | 26.1°C | 23.9°C | 9 mm | 75% | 6.5 m/s | 6.5 |
| 1998 | 25.6°C | 25.0°C | 24.5°C | 26.3°C | 23.4°C | 8 mm | 76% | 6.6 m/s | 6.2 |
| 1997 | 26.9°C | 26.2°C | 25.6°C | 28.3°C | 24.7°C | 16 mm | 77% | 6.2 m/s | 6.3 |
| 1996 | 27.2°C | 26.5°C | 25.8°C | 28.7°C | 24.8°C | 18 mm | 75% | 5.9 m/s | 6.1 |
| 1995 | 27.1°C | 26.3°C | 25.6°C | 28.7°C | 24.5°C | 10 mm | 73% | 4.7 m/s | 6.1 |
| 1994 | 26.3°C | 25.7°C | 25.1°C | 27.4°C | 24.2°C | 22 mm | 80% | 6.2 m/s | 5.8 |
| 1993 | 26.5°C | 25.8°C | 25.0°C | 28.1°C | 23.7°C | 18 mm | 77% | 4.9 m/s | 6 |
| 1992 | 26.5°C | 25.9°C | 25.3°C | 28.0°C | 23.9°C | 36 mm | 81% | 6.1 m/s | 5.5 |
| 1991 | 26.3°C | 25.6°C | 24.9°C | 27.8°C | 23.9°C | 26 mm | 79% | 5 m/s | 5.9 |
| 1990 | 26.4°C | 25.8°C | 25.2°C | 27.3°C | 24.4°C | 17 mm | 79% | 6.5 m/s | 5.9 |
| 1989 | 26.1°C | 25.4°C | 24.7°C | 27.2°C | 24.1°C | 17 mm | 77% | 6.4 m/s | 5.9 |
| 1988 | 26.5°C | 25.8°C | 25.1°C | 27.5°C | 24.4°C | 30 mm | 78% | 5.8 m/s | 6.1 |
| 1987 | 27.0°C | 26.3°C | 25.6°C | 28.2°C | 23.5°C | 50 mm | 78% | 5 m/s | 5.5 |
| 1986 | 27.0°C | 26.3°C | 25.6°C | 27.9°C | 24.9°C | 73 mm | 80% | 4.5 m/s | 5.4 |
| 1985 | 26.4°C | 25.6°C | 24.8°C | 27.5°C | 23.9°C | 28 mm | 76% | 4.7 m/s | 5.7 |
| 1984 | 26.1°C | 25.4°C | 24.8°C | 26.9°C | 24.1°C | 25 mm | 79% | 5.1 m/s | 5.7 |
| 1983 ❄️ | 25.4°C | 24.8°C | 24.1°C | 26.2°C | 23.1°C | 54 mm | 81% | 6 m/s | — |
| 1982 🌧️ | 25.8°C | 25.2°C | 24.7°C | 26.6°C | 23.6°C | 170 mm | 81% | 6 m/s | — |
| 1981 | 26.5°C | 25.8°C | 25.1°C | 27.6°C | 24.2°C | 38 mm | 79% | 5.6 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 26.8°C with lows near 25.3°C (mean 26.1°C), based on 45 years of NASA POWER data.
September averages 34 mm of rainfall in Kailua, one of the drier months. The wettest on record was 170 mm in 1982.
The hottest September reached 29.4°C in 2015. The coldest dipped to 23.1°C in 1983.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 1.2°C. Daytime highs moved from 26°C to 27.4°C and overnight lows from 24.7°C to 25.7°C over the same span.
September is one of the warmer months of the year in Kailua and one of the drier months, so plan for around 26.8°C daytime highs and 25.3°C at night.
Not quite — September is the 12th coolest month in Kailua, averaging 26.1°C.
For September in Kailua, pack light layers you can adjust through the day, with typical highs of 26.8°C and lows of 25.3°C.
Relative humidity in September averages 77% — quite humid.
Average wind speed in September is 5.8 m/s. The windiest September on record averaged 7.1 m/s (2005).
The wettest September on record was 1982 with 170 mm. On average, September sees 34 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 Kailua 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.
