May is close to San Mateo's year-round average, with average highs near 15.5°C and lows around 10.6°C (mean 13.1°C). It is one of the drier months, averaging 17 mm of rainfall and 85% relative humidity across the period.
May is close to San Mateo's year-round average. Across 45 years of records, the warmest May in San Mateo was 1997 — when the month averaged 15.4°C — while the coldest was 1999 at 11°C. Typical May days reach 15.5°C with nights near 10.6°C. The long-term May temperature trend is broadly flat.
May is one of the drier months in San Mateo, averaging 17 mm of rainfall. The wettest May on record was 1998 with 68 mm, while the driest was 2021 at 1 mm.
Relative humidity in San Mateo during May averages 85%. The most humid Mays were 2006 and 2009 at 89%, and the least humid was 1984 at 81%.
May receives about 6.7 kWh/m²/day of solar energy in San Mateo. The sunniest Mays were 2022 and 2025 at 7.5 kWh/m²/day, and the cloudiest was 2019 at 5.7.
Average wind speed in San Mateo during May is 4.1 m/s. The windiest May was 1981 at 4.9 m/s, while the calmest was 1992 at 3 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 13.1°C | 13.2°C | 13.0°C | 12.9°C | 13.2°C | +0.1°C |
| Avg High | 15.8°C | 15.6°C | 15.3°C | 15.1°C | 15.6°C | -0.2°C |
| Avg Low | 10.4°C | 10.8°C | 10.6°C | 10.6°C | 10.7°C | +0.3°C |
| Avg Rain | 7 mm | 29 mm | 20 mm | 15 mm | 11 mm | +4 mm |
May temperatures in San Mateo have stayed relatively stable across the record.
May has ranged from a record low of 7°C (1999) to a record high of 30.8°C (2008).
Rainfall in May is one of the drier months, averaging 17 mm, with a wettest year of 68 mm.
Daytime highs and overnight lows have shifted differently — highs fell about 0.2°C per decade while lows rose 0°C per decade, narrowing the gap between day and night.
A good time to visit San Mateo
May is a good time to visit San Mateo, with days averaging 15.5°C and nights around 10.6°C (mean 13.1°C, close to San Mateo's yearly average) and low rainfall. September and August 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 | 15.5°C | 13.2°C | 10.8°C | 20.7°C | 9.8°C | 4 mm | 85% | 4.5 m/s | 7.5 |
| 2024 | 15.7°C | 13.1°C | 10.5°C | 23.5°C | 9.1°C | 22 mm | 85% | 4 m/s | 7.2 |
| 2023 | 14.4°C | 12.6°C | 10.8°C | 19.1°C | 9.4°C | 22 mm | 88% | 3.6 m/s | 5.8 |
| 2022 | 15.6°C | 12.9°C | 10.1°C | 21.8°C | 8.5°C | 1 mm | 82% | 4.6 m/s | 7.5 |
| 2021 | 15.1°C | 12.6°C | 10.1°C | 20.4°C | 8.7°C | 1 mm | 84% | 4.8 m/s | 7.2 |
| 2020 | 17.2°C | 14.5°C | 11.8°C | 21.2°C | 9.7°C | 17 mm | 84% | 3.9 m/s | 7 |
| 2019 | 14.9°C | 13.0°C | 11.1°C | 16.9°C | 8.9°C | 65 mm | 86% | 4 m/s | 5.7 |
| 2018 | 14.9°C | 13.0°C | 11.0°C | 19.2°C | 9.5°C | 4 mm | 86% | 4.2 m/s | 6.5 |
| 2017 | 15.8°C | 13.2°C | 10.6°C | 21.7°C | 9.1°C | 3 mm | 85% | 3.9 m/s | 6.9 |
| 2016 | 15.9°C | 13.7°C | 11.5°C | 21.6°C | 10.6°C | 9 mm | 86% | 3.3 m/s | 6.3 |
| 2015 | 14.0°C | 12.4°C | 10.8°C | 18.9°C | 9.6°C | 12 mm | 86% | 3.8 m/s | 5.8 |
| 2014 | 17.0°C | 14.3°C | 11.6°C | 26.0°C | 10.1°C | 3 mm | 81% | 4 m/s | 7.3 |
| 2013 | 16.0°C | 13.5°C | 10.9°C | 24.4°C | 9.1°C | 4 mm | 82% | 4.4 m/s | 7 |
| 2012 | 14.5°C | 12.2°C | 9.8°C | 21.3°C | 8.6°C | 3 mm | 85% | 4.4 m/s | 7.2 |
| 2011 | 13.9°C | 11.8°C | 9.6°C | 20.9°C | 8.3°C | 25 mm | 84% | 4.7 m/s | 6.8 |
| 2010 | 13.9°C | 11.6°C | 9.4°C | 17.5°C | 7.7°C | 22 mm | 85% | 4.4 m/s | 6.8 |
| 2009 | 14.6°C | 12.3°C | 10.0°C | 20.1°C | 8.6°C | 29 mm | 89% | 3.6 m/s | 5.9 |
| 2008 | 15.0°C | 12.4°C | 9.9°C | 30.8°C | 7.3°C | 5 mm | 83% | 4 m/s | 6.7 |
| 2007 | 14.8°C | 12.4°C | 10.0°C | 25.8°C | 8.5°C | 11 mm | 83% | 3.9 m/s | 6.7 |
| 2006 | 15.3°C | 13.0°C | 10.7°C | 21.0°C | 9.4°C | 12 mm | 89% | 3.7 m/s | 7 |
| 2005 | 16.2°C | 14.2°C | 12.1°C | 18.0°C | 10.9°C | 62 mm | 88% | 4 m/s | 6.5 |
| 2004 | 15.3°C | 13.2°C | 11.2°C | 18.0°C | 9.6°C | 3 mm | 86% | 4.3 m/s | 7.3 |
| 2003 | 15.0°C | 12.6°C | 10.3°C | 18.7°C | 8.9°C | 23 mm | 86% | 4.2 m/s | 6.7 |
| 2002 | 14.3°C | 12.0°C | 9.7°C | 18.9°C | 8.2°C | 20 mm | 86% | 4.2 m/s | 7 |
| 2001 | 17.2°C | 14.1°C | 10.9°C | 27.5°C | 9.2°C | 1 mm | 83% | 3.5 m/s | 7.3 |
| 2000 | 15.8°C | 13.4°C | 10.9°C | 22.1°C | 8.8°C | 31 mm | 85% | 4.4 m/s | 6.9 |
| 1999 ❄️ | 13.3°C | 11.0°C | 8.7°C | 16.3°C | 7.0°C | 3 mm | 86% | 4.7 m/s | 6.7 |
| 1998 🌧️ | 14.5°C | 12.8°C | 11.1°C | 16.9°C | 9.6°C | 68 mm | 84% | 4.4 m/s | 6.4 |
| 1997 🔥 | 18.3°C | 15.4°C | 12.5°C | 27.6°C | 7.6°C | 10 mm | 84% | 3.3 m/s | 7.3 |
| 1996 | 16.0°C | 13.4°C | 10.8°C | 20.9°C | 8.8°C | 55 mm | 85% | 4.2 m/s | 7.1 |
| 1995 | 14.4°C | 12.4°C | 10.4°C | 16.8°C | 9.0°C | 24 mm | 88% | 3.4 m/s | 6.1 |
| 1994 | 15.2°C | 12.8°C | 10.5°C | 21.2°C | 8.9°C | 25 mm | 86% | 3.6 m/s | 6.5 |
| 1993 | 16.3°C | 14.0°C | 11.7°C | 23.1°C | 8.9°C | 27 mm | 86% | 3.8 m/s | 6.6 |
| 1992 | 17.8°C | 15.1°C | 12.3°C | 22.6°C | 11.0°C | 2 mm | 86% | 3 m/s | 6.3 |
| 1991 | 14.1°C | 11.7°C | 9.2°C | 18.1°C | 7.9°C | 9 mm | 84% | 4.2 m/s | 6.4 |
| 1990 | 15.9°C | 13.3°C | 10.8°C | 21.8°C | 9.3°C | 61 mm | 82% | 4.1 m/s | 6.4 |
| 1989 | 15.8°C | 13.3°C | 10.8°C | 22.5°C | 9.1°C | 4 mm | 84% | 4.4 m/s | 6.7 |
| 1988 | 15.4°C | 12.8°C | 10.2°C | 23.5°C | 8.2°C | 20 mm | 81% | 4.4 m/s | 7 |
| 1987 | 17.0°C | 14.2°C | 11.4°C | 22.2°C | 9.9°C | 2 mm | 82% | 4 m/s | 6.6 |
| 1986 | 15.5°C | 12.8°C | 10.0°C | 18.6°C | 7.8°C | 8 mm | 85% | 3.8 m/s | 6.5 |
| 1985 | 15.0°C | 12.5°C | 10.0°C | 18.7°C | 8.0°C | 5 mm | 83% | 4.2 m/s | 6.9 |
| 1984 | 16.5°C | 13.4°C | 10.3°C | 22.8°C | 8.0°C | 3 mm | 81% | 4.7 m/s | 7.3 |
| 1983 | 15.8°C | 13.3°C | 10.9°C | 22.1°C | 8.7°C | 9 mm | 84% | 4.2 m/s | — |
| 1982 | 15.3°C | 12.5°C | 9.6°C | 21.5°C | 8.0°C | 2 mm | 86% | 3.6 m/s | — |
| 1981 | 16.1°C | 13.3°C | 10.6°C | 20.2°C | 8.4°C | 10 mm | 83% | 4.9 m/s | — |
Actual recorded May data for each year, 1981–2025 — sourced from NASA POWER.
The average high in May is around 15.5°C with lows near 10.6°C (mean 13.1°C), based on 45 years of NASA POWER data.
May averages 17 mm of rainfall in San Mateo, one of the drier months. The wettest on record was 68 mm in 1998.
The hottest May reached 30.8°C in 2008. The coldest dipped to 7°C in 1999.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have fallen by about 0.1°C — but days and nights have moved in opposite directions. Overnight lows rose from 10.3°C to 10.5°C while daytime highs eased from 15.7°C to 15.3°C, narrowing the gap between day and night.
May is close to San Mateo's year-round average and one of the drier months, so plan for around 15.5°C daytime highs and 10.6°C at night.
Not quite — May is the 6th coolest month in San Mateo, averaging 13.1°C.
For May in San Mateo, pack light layers you can adjust through the day, with typical highs of 15.5°C and lows of 10.6°C.
Relative humidity in May averages 85% — quite humid.
Average wind speed in May is 4.1 m/s. The windiest May on record averaged 4.9 m/s (1981).
The wettest May on record was 1998 with 68 mm. On average, May sees 17 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 San Mateo 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.
