May is one of the warmer months of the year in Issaquah, with average highs near 15.5°C and lows around 6.2°C (mean 10.9°C). It is one of the drier months, averaging 102 mm of rainfall and 81% relative humidity across the period.
May is one of the warmer months of the year in Issaquah. Across 45 years of records, the warmest May in Issaquah was 2023 — when the month averaged 13.8°C — while the coldest were 1999 and 2011 at 8.3°C. Typical May days reach 15.5°C with nights near 6.2°C. The long-term trend is warming, about 0.2°C per decade.
May is one of the drier months in Issaquah, averaging 102 mm of rainfall. The wettest May on record was 1984 with 195 mm, while the driest was 2018 at 39 mm.
Relative humidity in Issaquah during May averages 81%. The most humid May was 1998 at 87%, and the least humid was 1992 at 74%.
May receives about 5.1 kWh/m²/day of solar energy in Issaquah. The sunniest May was 2023 at 6 kWh/m²/day, and the cloudiest were 1988 and 1991 at 4.3.
Average wind speed in Issaquah during May is 0.3 m/s. The windiest Mays were 2017, 2019 and 2021, among others at 0.3 m/s, while the calmest were 2023, 2024 and 2025, among others at 0.2 m/s.
Ranked against the other 11 months using 1981–2025 averages.
| Metric | 1980s | 1990s | 2000s | 2010s | 2020s | Change |
|---|---|---|---|---|---|---|
| Avg Temp | 10.4°C | 11.0°C | 10.7°C | 11.3°C | 10.7°C | +0.3°C |
| Avg High | 15.1°C | 15.6°C | 15.5°C | 16.0°C | 15.3°C | +0.2°C |
| Avg Low | 5.7°C | 6.3°C | 6.0°C | 6.7°C | 6.1°C | +0.4°C |
| Avg Rain | 107 mm | 98 mm | 100 mm | 96 mm | 114 mm | +7 mm |
May temperatures in Issaquah have risen by about 0.3°C between 1981–1985 and 2021–2025.
May has ranged from a record low of -1.7°C (1999) to a record high of 32.1°C (1983).
Rainfall in May is one of the drier months, averaging 102 mm, with a wettest year of 195 mm.
A good time to visit Issaquah
May is a good time to visit Issaquah, with days averaging 15.5°C and nights around 6.2°C (mean 10.9°C, warmer than Issaquah's yearly average) and higher rainfall. August and July 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 | 14.5°C | 9.5°C | 4.5°C | 25.2°C | -0.3°C | 80 mm | 83% | 0.2 m/s | 5.8 |
| 2024 | 14.1°C | 9.6°C | 5.1°C | 26.9°C | -0.4°C | 118 mm | 84% | 0.2 m/s | 5.4 |
| 2023 🔥 | 18.8°C | 13.8°C | 8.9°C | 30.6°C | 3.9°C | 61 mm | 81% | 0.2 m/s | 6 |
| 2022 | 12.9°C | 8.9°C | 4.8°C | 20.4°C | 1.8°C | 179 mm | 85% | 0.2 m/s | 4.5 |
| 2021 | 15.1°C | 10.6°C | 6.1°C | 22.0°C | 2.6°C | 79 mm | 81% | 0.3 m/s | 5.6 |
| 2020 | 16.5°C | 11.7°C | 6.9°C | 27.6°C | 0.2°C | 165 mm | 81% | 0.2 m/s | 5.2 |
| 2019 | 17.7°C | 12.7°C | 7.7°C | 25.9°C | 3.0°C | 57 mm | 79% | 0.3 m/s | 5.5 |
| 2018 | 18.1°C | 13.4°C | 8.7°C | 29.6°C | 4.7°C | 39 mm | 81% | 0.2 m/s | 5.8 |
| 2017 | 16.9°C | 11.8°C | 6.7°C | 26.8°C | 2.6°C | 93 mm | 80% | 0.3 m/s | 5.5 |
| 2016 | 16.8°C | 12.2°C | 7.5°C | 26.3°C | 3.8°C | 78 mm | 81% | 0.3 m/s | 5.4 |
| 2015 | 17.0°C | 12.4°C | 7.8°C | 24.4°C | 2.5°C | 40 mm | 81% | 0.3 m/s | 5.4 |
| 2014 | 16.6°C | 12.2°C | 7.8°C | 29.2°C | 4.3°C | 121 mm | 82% | 0.3 m/s | 5.2 |
| 2013 | 16.5°C | 11.6°C | 6.6°C | 25.6°C | 0.0°C | 102 mm | 81% | 0.3 m/s | 5.1 |
| 2012 | 14.8°C | 9.9°C | 5.1°C | 25.8°C | 0.6°C | 117 mm | 78% | 0.3 m/s | 5.4 |
| 2011 | 12.5°C | 8.3°C | 4.2°C | 19.1°C | 0.9°C | 146 mm | 85% | 0.2 m/s | 4.7 |
| 2010 | 12.7°C | 8.6°C | 4.4°C | 20.3°C | -0.7°C | 171 mm | 84% | 0.3 m/s | 4.8 |
| 2009 | 15.7°C | 10.6°C | 5.6°C | 25.2°C | 1.8°C | 128 mm | 79% | 0.3 m/s | 5.7 |
| 2008 | 15.6°C | 10.9°C | 6.3°C | 27.8°C | 0.9°C | 90 mm | 82% | 0.2 m/s | 4.6 |
| 2007 | 16.0°C | 10.8°C | 5.6°C | 26.5°C | 1.6°C | 62 mm | 79% | 0.2 m/s | 5.8 |
| 2006 | 16.6°C | 11.3°C | 6.0°C | 25.5°C | 0.5°C | 100 mm | 79% | 0.3 m/s | 5.5 |
| 2005 | 17.3°C | 12.5°C | 7.6°C | 32.0°C | 3.5°C | 130 mm | 81% | 0.2 m/s | 4.9 |
| 2004 | 15.3°C | 11.2°C | 7.0°C | 22.1°C | 3.9°C | 137 mm | 84% | 0.3 m/s | 4.6 |
| 2003 | 14.6°C | 10.1°C | 5.5°C | 24.8°C | 0.7°C | 63 mm | 82% | 0.3 m/s | 5.1 |
| 2002 | 13.7°C | 9.3°C | 4.9°C | 21.4°C | -1.1°C | 95 mm | 82% | 0.3 m/s | 4.9 |
| 2001 | 16.2°C | 10.9°C | 5.7°C | 31.4°C | -0.2°C | 81 mm | 77% | 0.3 m/s | 5.8 |
| 2000 | 13.8°C | 9.8°C | 5.7°C | 20.3°C | 1.5°C | 114 mm | 83% | 0.3 m/s | 4.9 |
| 1999 ❄️ | 12.9°C | 8.3°C | 3.7°C | 25.9°C | -1.7°C | 112 mm | 82% | 0.3 m/s | 5.3 |
| 1998 | 14.1°C | 10.3°C | 6.4°C | 29.3°C | 1.6°C | 118 mm | 87% | 0.2 m/s | 4.7 |
| 1997 | 17.3°C | 12.5°C | 7.7°C | 25.7°C | 0.4°C | 94 mm | 81% | 0.3 m/s | 5.3 |
| 1996 | 12.4°C | 8.4°C | 4.4°C | 20.6°C | 0.6°C | 151 mm | 84% | 0.2 m/s | 4.6 |
| 1995 | 17.1°C | 12.3°C | 7.5°C | 23.0°C | 2.2°C | 57 mm | 77% | 0.3 m/s | 5.6 |
| 1994 | 16.4°C | 11.7°C | 6.9°C | 23.5°C | 2.7°C | 74 mm | 79% | 0.3 m/s | 4.8 |
| 1993 | 18.3°C | 13.1°C | 7.8°C | 29.3°C | 2.0°C | 130 mm | 81% | 0.2 m/s | 4.4 |
| 1992 | 19.1°C | 13.4°C | 7.7°C | 30.0°C | 1.7°C | 42 mm | 74% | 0.3 m/s | 5.8 |
| 1991 | 13.5°C | 9.5°C | 5.5°C | 18.2°C | 2.4°C | 94 mm | 85% | 0.2 m/s | 4.3 |
| 1990 | 14.8°C | 10.1°C | 5.5°C | 26.2°C | 2.1°C | 111 mm | 83% | 0.2 m/s | 4.6 |
| 1989 | 14.9°C | 10.4°C | 5.9°C | 24.7°C | 2.0°C | 99 mm | 82% | 0.3 m/s | 4.6 |
| 1988 | 15.0°C | 10.1°C | 5.2°C | 27.2°C | 0.5°C | 132 mm | 82% | 0.3 m/s | 4.3 |
| 1987 | 16.6°C | 11.5°C | 6.5°C | 30.4°C | 2.5°C | 103 mm | 79% | 0.3 m/s | 5.3 |
| 1986 | 14.9°C | 10.5°C | 6.1°C | 27.6°C | 0.9°C | 130 mm | 82% | 0.3 m/s | 4.4 |
| 1985 | 15.5°C | 10.7°C | 5.8°C | 25.2°C | -0.1°C | 76 mm | 81% | 0.3 m/s | 5 |
| 1984 🌧️ | 12.6°C | 8.5°C | 4.4°C | 25.0°C | 1.4°C | 195 mm | 84% | 0.2 m/s | 4.9 |
| 1983 | 16.8°C | 12.0°C | 7.1°C | 32.1°C | 1.9°C | 80 mm | 79% | 0.3 m/s | — |
| 1982 | 14.9°C | 10.0°C | 5.1°C | 24.6°C | 1.3°C | 48 mm | 78% | 0.3 m/s | — |
| 1981 | 14.4°C | 10.0°C | 5.5°C | 27.1°C | 2.0°C | 100 mm | 83% | 0.2 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 6.2°C (mean 10.9°C), based on 45 years of NASA POWER data.
May averages 102 mm of rainfall in Issaquah, one of the drier months. The wettest on record was 195 mm in 1984.
The hottest May reached 32.1°C in 1983. The coldest dipped to -1.7°C in 1999.
Comparing the earliest years on record (1981–1985) with the most recent (2021–2025), average May temperatures have risen by about 0.3°C. Daytime highs moved from 14.8°C to 15.1°C and overnight lows from 5.6°C to 5.9°C over the same span.
May is one of the warmer months of the year in Issaquah and one of the drier months, so plan for around 15.5°C daytime highs and 6.2°C at night.
Not quite — May is the 8th coolest month in Issaquah, averaging 10.9°C.
For May in Issaquah, pack warm layers and a jacket for chilly mornings, with typical highs of 15.5°C and lows of 6.2°C. Bring an umbrella or light rain jacket too.
Relative humidity in May averages 81% — quite humid.
Average wind speed in May is 0.3 m/s. The windiest May on record averaged 0.3 m/s (1982).
The wettest May on record was 1984 with 195 mm. On average, May sees 102 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 Issaquah 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.
