August weather in Mercer Island, WA
The average temperature in Mercer Island in August is 67.8°F (58.1°F–77.4°F). Average precipitation: 0.83 inches.
August is a summer month in Mercer Island, and is warmer than the annual average of 53.8°F. Daily temperatures swing about 19.3°F between overnight low and afternoon high. Expect about 4 days with precipitation. Daylight averages about 14h 5m. For travel, August is one of the best months of the year to visit.
Avg High
77.4°F
Avg Low
58.1°F
Precipitation
0.83 in
Daylight
14h 5m
August records in Mercer Island
| Date | Record High | Record Low | Record Precip |
|---|---|---|---|
| August 1 | 95.0°F (1949) | 51.1°F (1953) | 0.25 in (1964) |
| August 2 | 91.0°F (2009) | 48.9°F (1953) | 0.42 in (1956) |
| August 3 | 90.0°F (2017) | 48.0°F (1956) | 0.25 in (1957) |
| August 4 | 93.9°F (1952) | 46.9°F (1950) | 0.59 in (1962) |
| August 5 | 91.9°F (2012) | 52.0°F (1948) | 0.46 in (1948) |
| August 6 | 87.1°F (2013) | 51.1°F (1959) | 0.93 in (2004) |
| August 7 | 89.1°F (1965) | 51.1°F (1948) | 0.34 in (1957) |
| August 8 | 99.0°F (1960) | 52.0°F (1948) | 0.31 in (2021) |
| August 9 | 100.0°F (1960) | 50.0°F (1955) | 0.29 in (1957) |
| August 10 | 90.0°F (2001) | 50.0°F (1954) | 0.19 in (1965) |
| August 11 | 95.0°F (2014) | 51.1°F (1954) | 0.31 in (2009) |
| August 12 | 91.0°F (2025) | 52.0°F (2000) | 0.34 in (1965) |
| August 13 | 91.9°F (2021) | 48.0°F (1955) | 0.29 in (2009) |
| August 14 | 93.9°F (2023) | 48.0°F (1955) | 0.82 in (2015) |
| August 15 | 95.0°F (2010) | 48.0°F (1955) | 1.04 in (1950) |
| August 16 | 98.1°F (2020) | 52.0°F (2011) | 0.36 in (1954) |
| August 17 | 91.0°F (2012) | 50.0°F (2000) | 0.51 in (2024) |
| August 18 | 89.1°F (2022) | 48.9°F (1951) | 0.28 in (1954) |
| August 19 | 91.9°F (2015) | 51.1°F (1949) | 0.87 in (1965) |
| August 20 | 87.1°F (1950) | 48.0°F (1952) | 0.40 in (2008) |
| August 21 | 89.1°F (1950) | 50.0°F (1955) | 0.45 in (2001) |
| August 22 | 90.0°F (2018) | 46.0°F (1960) | 1.58 in (2001) |
| August 23 | 87.1°F (2025) | 48.9°F (1955) | 0.43 in (1960) |
| August 24 | 90.0°F (2025) | 46.9°F (1951) | 0.68 in (2004) |
| August 25 | 90.0°F (2022) | 48.0°F (1954) | 0.43 in (2008) |
| August 26 | 89.1°F (1950) | 46.9°F (1949) | 0.34 in (1953) |
| August 27 | 88.0°F (2009) | 48.0°F (1952) | 0.55 in (1951) |
| August 28 | 88.0°F (2017) | 48.0°F (1952) | 0.30 in (2005) |
| August 29 | 87.1°F (2017) | 46.9°F (1951) | 0.46 in (2013) |
| August 30 | 86.0°F (2022) | 46.0°F (1950) | 0.27 in (2015) |
| August 31 | 87.1°F (2022) | 48.9°F (1956) | 0.60 in (1961) |