September is one of the warmer months of the year in Hilo, with average highs near 25.2°C and lows around 21.1°C (mean 23.2°C). It is about average for rainfall, averaging 145 mm of rainfall and 82% relative humidity across the period.
September is one of the warmer months of the year in Hilo. Across 45 years of records, the warmest September in Hilo was 2015 — when the month averaged 24.4°C — while the coldest were 1983, 2011 and 2012 at 21.9°C. Typical September days reach 25.2°C with nights near 21.1°C. The long-term September temperature trend is broadly flat.
September is about average for rainfall in Hilo, averaging 145 mm of rainfall. The wettest September on record was 1982 with 1561 mm, while the driest was 1995 at 3 mm.
Relative humidity in Hilo during September averages 82%. The most humid September was 1983 at 86%, and the least humid was 1995 at 73%.
September receives about 5.6 kWh/m²/day of solar energy in Hilo. The sunniest September was 2004 at 6 kWh/m²/day, and the cloudiest was 1986 at 5.
Average wind speed in Hilo during September is 4 m/s. The windiest September was 1998 at 4.7 m/s, while the calmest was 2014 at 3.1 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 22.9°C | 23.5°C | 22.7°C | 23.1°C | 23.3°C | +0.4°C |
| Avg High | 25.0°C | 25.7°C | 24.7°C | 25.1°C | 25.4°C | +0.4°C |
| Avg Low | 20.9°C | 21.2°C | 20.9°C | 21.2°C | 21.2°C | +0.3°C |
| Avg Rain | 272 mm | 29 mm | 224 mm | 113 mm | 73 mm | -198 mm |
September temperatures in Hilo have risen by about 0.6°C between 1981–1985 and 2021–2025.
September has ranged from a record low of 18.8°C (2011) to a record high of 29.1°C (2015).
Rainfall in September is about average for rainfall, averaging 145 mm, with a wettest year of 1561 mm.
A good time to visit Hilo
September is a good time to visit Hilo, with days averaging 25.2°C and nights around 21.1°C (mean 23.2°C, warmer than Hilo's yearly average) and higher rainfall. June and May are marginally more temperate, but September still suits most travellers.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 25.6°C | 23.4°C | 21.1°C | 27.1°C | 20.2°C | 90 mm | 81% | 3.7 m/s | 5.7 |
| 2024 | 25.5°C | 23.5°C | 21.5°C | 27.1°C | 20.1°C | 45 mm | 83% | 4 m/s | 5.9 |
| 2023 | 25.2°C | 23.1°C | 21.1°C | 26.4°C | 20.4°C | 55 mm | 83% | 4.1 m/s | 5.9 |
| 2022 | 25.6°C | 23.4°C | 21.2°C | 26.7°C | 20.4°C | 97 mm | 82% | 3.7 m/s | 5.8 |
| 2021 | 24.9°C | 22.9°C | 20.8°C | 25.7°C | 20.0°C | 125 mm | 81% | 4.1 m/s | 5.7 |
| 2020 | 25.8°C | 23.5°C | 21.2°C | 27.0°C | 20.6°C | 29 mm | 80% | 3.9 m/s | 5.9 |
| 2019 | 25.9°C | 24.0°C | 22.2°C | 27.1°C | 21.3°C | 113 mm | 85% | 3.5 m/s | 5.7 |
| 2018 | 26.1°C | 24.1°C | 22.0°C | 28.1°C | 20.8°C | 184 mm | 84% | 3.7 m/s | 5.9 |
| 2017 | 25.4°C | 23.4°C | 21.4°C | 26.8°C | 20.6°C | 100 mm | 82% | 3.6 m/s | 5.5 |
| 2016 | 25.1°C | 23.3°C | 21.5°C | 26.9°C | 20.4°C | 143 mm | 85% | 3.8 m/s | 5.4 |
| 2015 🔥 | 26.1°C | 24.4°C | 22.7°C | 29.1°C | 21.1°C | 234 mm | 85% | 4 m/s | 5.2 |
| 2014 | 25.6°C | 23.6°C | 21.6°C | 26.9°C | 20.4°C | 58 mm | 83% | 3.1 m/s | 5.4 |
| 2013 | 24.7°C | 22.7°C | 20.7°C | 26.1°C | 19.9°C | 71 mm | 82% | 4 m/s | 5.8 |
| 2012 | 23.7°C | 21.9°C | 20.0°C | 24.8°C | 19.4°C | 95 mm | 82% | 4.3 m/s | 5.5 |
| 2011 | 23.9°C | 21.9°C | 20.0°C | 24.6°C | 18.8°C | 105 mm | 84% | 3.7 m/s | 5.4 |
| 2010 | 24.2°C | 22.0°C | 19.9°C | 25.3°C | 19.2°C | 26 mm | 81% | 3.8 m/s | 5.9 |
| 2009 | 24.5°C | 22.7°C | 20.9°C | 25.5°C | 19.6°C | 194 mm | 84% | 4.3 m/s | 5.8 |
| 2008 | 24.1°C | 22.1°C | 20.2°C | 25.6°C | 19.2°C | 208 mm | 83% | 3.9 m/s | 5.6 |
| 2007 | 24.3°C | 22.6°C | 21.0°C | 25.3°C | 20.5°C | 260 mm | 85% | 4.5 m/s | 5.3 |
| 2006 | 24.3°C | 22.6°C | 20.8°C | 25.3°C | 19.8°C | 237 mm | 84% | 4.2 m/s | 5.5 |
| 2005 | 24.7°C | 23.1°C | 21.4°C | 26.9°C | 20.1°C | 562 mm | 85% | 4.6 m/s | 5.5 |
| 2004 | 25.2°C | 23.2°C | 21.2°C | 26.2°C | 20.1°C | 106 mm | 81% | 3.9 m/s | 6 |
| 2003 | 25.0°C | 23.0°C | 21.0°C | 26.3°C | 20.2°C | 139 mm | 83% | 4 m/s | 5.8 |
| 2002 | 24.1°C | 22.3°C | 20.6°C | 25.5°C | 19.8°C | 259 mm | 84% | 4.1 m/s | 5.2 |
| 2001 | 24.8°C | 22.7°C | 20.7°C | 26.5°C | 20.0°C | 204 mm | 82% | 4.1 m/s | 5.8 |
| 2000 | 25.5°C | 23.2°C | 20.8°C | 26.3°C | 19.1°C | 68 mm | 79% | 4.2 m/s | 5.6 |
| 1999 | 24.5°C | 22.3°C | 20.0°C | 25.9°C | 19.6°C | 8 mm | 77% | 4.5 m/s | 5.6 |
| 1998 | 24.8°C | 22.5°C | 20.2°C | 26.1°C | 19.5°C | 6 mm | 78% | 4.7 m/s | 5.6 |
| 1997 | 26.2°C | 23.9°C | 21.5°C | 27.5°C | 20.5°C | 27 mm | 78% | 4.3 m/s | 5.5 |
| 1996 | 26.4°C | 24.0°C | 21.7°C | 27.9°C | 20.5°C | 5 mm | 76% | 4.4 m/s | 5.4 |
| 1995 | 26.6°C | 23.9°C | 21.3°C | 28.1°C | 20.3°C | 3 mm | 73% | 3.9 m/s | 5.8 |
| 1994 | 26.0°C | 23.8°C | 21.6°C | 27.8°C | 20.3°C | 6 mm | 80% | 4.4 m/s | 5.5 |
| 1993 | 26.2°C | 23.8°C | 21.3°C | 27.6°C | 20.1°C | 4 mm | 77% | 3.7 m/s | 5.4 |
| 1992 | 26.2°C | 24.2°C | 22.1°C | 27.3°C | 20.9°C | 8 mm | 82% | 4.5 m/s | 5.3 |
| 1991 | 25.2°C | 23.0°C | 20.9°C | 26.9°C | 19.7°C | 194 mm | 81% | 3.8 m/s | 5.6 |
| 1990 | 25.3°C | 23.4°C | 21.5°C | 26.4°C | 20.6°C | 26 mm | 82% | 4.4 m/s | 5.2 |
| 1989 | 25.0°C | 22.8°C | 20.6°C | 26.1°C | 19.6°C | 10 mm | 78% | 4.5 m/s | 5.6 |
| 1988 | 25.2°C | 23.1°C | 21.0°C | 26.4°C | 19.4°C | 26 mm | 79% | 4.1 m/s | 5.2 |
| 1987 | 25.6°C | 23.7°C | 21.9°C | 27.4°C | 21.0°C | 91 mm | 83% | 3.7 m/s | 5.2 |
| 1986 | 25.4°C | 23.6°C | 21.7°C | 27.7°C | 20.4°C | 312 mm | 85% | 3.3 m/s | 5 |
| 1985 | 25.0°C | 23.0°C | 20.9°C | 27.2°C | 20.1°C | 45 mm | 83% | 3.6 m/s | 5.7 |
| 1984 | 24.7°C | 22.5°C | 20.4°C | 25.7°C | 19.5°C | 14 mm | 83% | 3.4 m/s | 5.6 |
| 1983 ❄️ | 23.8°C | 21.9°C | 20.0°C | 24.6°C | 19.1°C | 373 mm | 86% | 3.9 m/s | — |
| 1982 🌧️ | 24.2°C | 22.5°C | 20.8°C | 25.8°C | 19.7°C | 1561 mm | 85% | 3.8 m/s | — |
| 1981 | 25.9°C | 23.4°C | 21.0°C | 27.4°C | 19.2°C | 13 mm | 80% | 3.9 m/s | — |
Actual recorded September data for each year, 1981–2025 — sourced from NASA POWER.
The average high in September is around 25.2°C with lows near 21.1°C (mean 23.2°C), based on 45 years of NASA POWER data.
September averages 145 mm of rainfall in Hilo, about average for rainfall. The wettest on record was 1561 mm in 1982.
The hottest September reached 29.1°C in 2015. The coldest dipped to 18.8°C in 2011.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average September temperatures have risen by about 0.6°C. Daytime highs moved from 24.7°C to 25.4°C and overnight lows from 20.6°C to 21.1°C over the same span.
September is one of the warmer months of the year in Hilo and about average for rainfall, so plan for around 25.2°C daytime highs and 21.1°C at night.
Not quite — September is the 12th coolest month in Hilo, averaging 23.2°C.
For September in Hilo, pack light layers you can adjust through the day, with typical highs of 25.2°C and lows of 21.1°C. Bring an umbrella or light rain jacket too.
Relative humidity in September averages 82% — quite humid.
Average wind speed in September is 4 m/s. The windiest September on record averaged 4.7 m/s (1998).
The wettest September on record was 1982 with 1561 mm. On average, September sees 145 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 Hilo 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.
