May is close to Fullerton's year-round average, with average highs near 24°C and lows around 12.1°C (mean 18.1°C). It is one of the drier months, averaging 8 mm of rainfall and 62% relative humidity across the period.
May is close to Fullerton's year-round average. Across 45 years of records, the warmest May in Fullerton was 1997 — when the month averaged 22°C — while the coldest was 1998 at 14.8°C. Typical May days reach 24°C with nights near 12.1°C. The long-term trend is cooling, about 0.2°C per decade.
May is one of the drier months in Fullerton, averaging 8 mm of rainfall. The wettest May on record was 1998 with 74 mm, while the driest were 1984, 2004 and 2007 at 0 mm.
Relative humidity in Fullerton during May averages 62%. The most humid May was 2023 at 77%, and the least humid was 1984 at 41%.
May receives about 6.8 kWh/m²/day of solar energy in Fullerton. The sunniest Mays were 2014 and 2020 at 7.7 kWh/m²/day, and the cloudiest were 1994, 1995 and 2023 at 5.8.
Average wind speed in Fullerton during May is 2.1 m/s. The windiest Mays were 1988, 1990 and 1991 at 2.5 m/s, while the calmest were 1992 and 2001 at 1.8 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 18.6°C | 17.6°C | 18.6°C | 17.5°C | 17.8°C | -0.8°C |
| Avg High | 25.0°C | 23.4°C | 24.6°C | 23.2°C | 23.5°C | -1.5°C |
| Avg Low | 12.2°C | 11.8°C | 12.4°C | 11.8°C | 12.1°C | -0.1°C |
| Avg Rain | 3 mm | 12 mm | 7 mm | 10 mm | 5 mm | +2 mm |
May temperatures in Fullerton have fallen by about 0.9°C between 1981–1985 and 2021–2025.
May has ranged from a record low of 5.7°C (1991) to a record high of 35°C (2004).
Rainfall in May is one of the drier months, averaging 8 mm, with a wettest year of 74 mm.
Daytime highs and overnight lows have shifted differently — highs fell about 0.4°C per decade while lows rose 0°C per decade, narrowing the gap between day and night.
A good time to visit Fullerton
May is a good time to visit Fullerton, with days averaging 24°C and nights around 12.1°C (mean 18.1°C, close to Fullerton's yearly average) and low rainfall. June and September are marginally more temperate, but May still suits most travellers.
| Year | Avg High | Avg Temp | Avg Low | Hottest Day | Coldest Day | Rainfall | Humidity | Wind | Solar |
|---|---|---|---|---|---|---|---|---|---|
| 2025 | 24.4°C | 18.8°C | 13.2°C | 31.8°C | 9.8°C | 5 mm | 65% | 1.9 m/s | 6.7 |
| 2024 | 21.6°C | 16.3°C | 11.1°C | 24.2°C | 7.5°C | 3 mm | 75% | 1.9 m/s | 6.3 |
| 2023 | 20.3°C | 16.0°C | 11.8°C | 25.9°C | 8.9°C | 17 mm | 77% | 2.1 m/s | 5.8 |
| 2022 | 25.0°C | 18.4°C | 11.9°C | 32.6°C | 7.0°C | 0 mm | 58% | 2.1 m/s | 7.2 |
| 2021 | 24.8°C | 18.3°C | 11.9°C | 31.0°C | 9.0°C | 1 mm | 61% | 2.1 m/s | 7.1 |
| 2020 | 25.1°C | 19.1°C | 13.0°C | 31.7°C | 9.8°C | 3 mm | 63% | 2 m/s | 7.7 |
| 2019 | 20.1°C | 15.5°C | 10.9°C | 24.4°C | 7.7°C | 37 mm | 77% | 2.2 m/s | 6.2 |
| 2018 | 22.5°C | 17.4°C | 12.4°C | 29.5°C | 9.8°C | 5 mm | 68% | 2.2 m/s | 6.4 |
| 2017 | 23.4°C | 17.7°C | 12.1°C | 31.3°C | 7.2°C | 8 mm | 64% | 2 m/s | 6.8 |
| 2016 | 22.5°C | 17.2°C | 12.0°C | 28.5°C | 10.0°C | 7 mm | 69% | 2.1 m/s | 6.5 |
| 2015 | 21.8°C | 16.9°C | 11.9°C | 28.9°C | 9.1°C | 17 mm | 67% | 2.2 m/s | 6.2 |
| 2014 | 26.8°C | 20.2°C | 13.6°C | 35.0°C | 9.6°C | 1 mm | 50% | 2.2 m/s | 7.7 |
| 2013 | 25.7°C | 19.3°C | 12.8°C | 33.2°C | 10.8°C | 11 mm | 56% | 2.1 m/s | 7.4 |
| 2012 | 25.3°C | 18.6°C | 11.8°C | 31.2°C | 8.9°C | 1 mm | 56% | 2 m/s | 7.3 |
| 2011 | 21.9°C | 16.2°C | 10.5°C | 30.6°C | 7.2°C | 13 mm | 62% | 2.3 m/s | 7.3 |
| 2010 | 22.3°C | 16.2°C | 10.1°C | 28.0°C | 6.3°C | 2 mm | 61% | 2.2 m/s | 7.6 |
| 2009 | 26.1°C | 19.7°C | 13.2°C | 33.4°C | 10.7°C | 0 mm | 58% | 1.9 m/s | 6.9 |
| 2008 | 23.5°C | 17.7°C | 11.8°C | 34.7°C | 8.0°C | 7 mm | 59% | 2.1 m/s | 6.9 |
| 2007 | 24.4°C | 17.9°C | 11.3°C | 32.4°C | 8.7°C | 0 mm | 54% | 2 m/s | 7 |
| 2006 | 24.6°C | 18.7°C | 12.8°C | 30.2°C | 9.6°C | 18 mm | 64% | 1.9 m/s | 6.4 |
| 2005 | 23.5°C | 18.1°C | 12.6°C | 30.4°C | 7.9°C | 11 mm | 70% | 2 m/s | 7.2 |
| 2004 | 25.8°C | 19.6°C | 13.3°C | 35.0°C | 9.6°C | 0 mm | 54% | 2.2 m/s | 7.5 |
| 2003 | 23.1°C | 17.4°C | 11.6°C | 33.2°C | 6.6°C | 27 mm | 63% | 2 m/s | 6.6 |
| 2002 | 23.9°C | 17.4°C | 10.9°C | 31.0°C | 7.7°C | 3 mm | 58% | 2.1 m/s | 7.1 |
| 2001 | 26.3°C | 20.0°C | 13.8°C | 31.5°C | 10.0°C | 1 mm | 61% | 1.8 m/s | 6.3 |
| 2000 | 25.1°C | 19.1°C | 13.1°C | 31.4°C | 7.9°C | 5 mm | 59% | 2.1 m/s | 6.9 |
| 1999 | 22.9°C | 16.8°C | 10.6°C | 26.7°C | 7.2°C | 1 mm | 62% | 2.1 m/s | 6.6 |
| 1998 ❄️ 🌧️ | 19.1°C | 14.8°C | 10.5°C | 22.5°C | 8.6°C | 74 mm | 76% | 2.2 m/s | 6.6 |
| 1997 🔥 | 28.6°C | 22.0°C | 15.5°C | 34.1°C | 11.3°C | 0 mm | 54% | 2 m/s | 7.2 |
| 1996 | 25.3°C | 19.0°C | 12.8°C | 30.6°C | 9.8°C | 2 mm | 58% | 2.2 m/s | 7.5 |
| 1995 | 19.7°C | 15.1°C | 10.5°C | 26.2°C | 7.3°C | 9 mm | 75% | 2.3 m/s | 5.8 |
| 1994 | 22.5°C | 16.8°C | 11.2°C | 27.7°C | 9.0°C | 9 mm | 67% | 2 m/s | 5.8 |
| 1993 | 24.0°C | 18.2°C | 12.5°C | 29.5°C | 9.2°C | 0 mm | 66% | 2.1 m/s | 7 |
| 1992 | 25.0°C | 19.3°C | 13.6°C | 28.0°C | 10.8°C | 3 mm | 70% | 1.8 m/s | 6.1 |
| 1991 | 22.4°C | 16.1°C | 9.8°C | 28.7°C | 5.7°C | 1 mm | 61% | 2.5 m/s | 6.8 |
| 1990 | 24.1°C | 17.7°C | 11.3°C | 34.7°C | 9.5°C | 22 mm | 57% | 2.5 m/s | 6.8 |
| 1989 | 24.8°C | 18.5°C | 12.2°C | 29.3°C | 8.4°C | 3 mm | 54% | 2.3 m/s | 6.7 |
| 1988 | 25.0°C | 18.5°C | 12.0°C | 32.3°C | 6.1°C | 2 mm | 52% | 2.5 m/s | 6.8 |
| 1987 | 25.9°C | 19.7°C | 13.5°C | 31.9°C | 9.0°C | 4 mm | 53% | 2.1 m/s | 6.2 |
| 1986 | 24.5°C | 18.1°C | 11.7°C | 31.3°C | 6.9°C | 0 mm | 55% | 2 m/s | 7.1 |
| 1985 | 23.8°C | 17.5°C | 11.3°C | 28.9°C | 8.1°C | 3 mm | 55% | 2.1 m/s | 6.6 |
| 1984 | 29.2°C | 21.8°C | 14.4°C | 33.3°C | 8.7°C | 0 mm | 41% | 2.4 m/s | 6.5 |
| 1983 | 23.9°C | 17.6°C | 11.3°C | 29.2°C | 6.5°C | 3 mm | 65% | 2.2 m/s | — |
| 1982 | 23.0°C | 17.2°C | 11.4°C | 28.1°C | 7.7°C | 6 mm | 65% | 2 m/s | — |
| 1981 | 24.8°C | 18.2°C | 11.7°C | 30.1°C | 8.5°C | 3 mm | 56% | 2.3 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 24°C with lows near 12.1°C (mean 18.1°C), based on 45 years of NASA POWER data.
May averages 8 mm of rainfall in Fullerton, one of the drier months. The wettest on record was 74 mm in 1998.
The hottest May reached 35°C in 2004. The coldest dipped to 5.7°C in 1991.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have fallen by about 0.9°C. Daytime highs moved from 24.9°C to 23.2°C and overnight lows from 12°C to 12°C over the same span.
May is close to Fullerton's year-round average and one of the drier months, so plan for around 24°C daytime highs and 12.1°C at night.
Not quite — May is the 7th coolest month in Fullerton, averaging 18.1°C.
For May in Fullerton, pack light layers you can adjust through the day, with typical highs of 24°C and lows of 12.1°C.
Relative humidity in May averages 62% — moderately humid.
Average wind speed in May is 2.1 m/s. The windiest May on record averaged 2.5 m/s (1988).
The wettest May on record was 1998 with 74 mm. On average, May sees 8 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 Fullerton behaves each May, 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 May specifically, along with year-by-year records and how the month has changed over the decades.
