September weather in Issaquah, WA
The average temperature in Issaquah in September is 62.4°F (53.1°F–71.6°F). Average precipitation: 1.53 inches.
September is a fall month in Issaquah, and is warmer than the annual average of 53.6°F. Daily temperatures swing about 18.5°F between overnight low and afternoon high. Expect about 9 days with precipitation. Daylight averages about 12h 19m. For travel, September is one of the best months of the year to visit.
Avg High
71.6°F
Avg Low
53.1°F
Precipitation
1.53 in
Daylight
12h 19m
September records in Issaquah
| Date | Record High | Record Low | Record Precip |
|---|---|---|---|
| September 1 | 90.0°F (2006) | 46.0°F (2021) | 0.29 in (2004) |
| September 2 | 89.1°F (2006) | 46.9°F (2008) | 0.32 in (2014) |
| September 3 | 89.1°F (2003) | 50.0°F (2008) | 0.21 in (2007) |
| September 4 | 87.1°F (2017) | 46.9°F (2002) | 0.66 in (2007) |
| September 5 | 90.0°F (2024) | 46.0°F (2015) | 0.94 in (2013) |
| September 6 | 89.1°F (2024) | 46.9°F (2002) | 0.99 in (2009) |
| September 7 | 89.1°F (2012) | 50.0°F (2000) | 0.41 in (2019) |
| September 8 | 87.1°F (1999) | 46.9°F (2002) | 0.21 in (2010) |
| September 9 | 88.0°F (2020) | 48.9°F (2001) | 0.16 in (2000) |
| September 10 | 91.0°F (2020) | 48.9°F (2008) | 0.60 in (2004) |
| September 11 | 89.1°F (2013) | 46.9°F (2014) | 0.16 in (2003) |
| September 12 | 84.0°F (1999) | 48.0°F (2012) | 0.92 in (2004) |
| September 13 | 90.0°F (1999) | 46.0°F (2003) | 0.28 in (2004) |
| September 14 | 88.0°F (2000) | 48.9°F (2014) | 0.72 in (2006) |
| September 15 | 86.0°F (2014) | 46.9°F (2003) | 0.18 in (2010) |
| September 16 | 91.0°F (2025) | 46.0°F (2021) | 0.81 in (2003) |
| September 17 | 81.0°F (2012) | 48.0°F (2018) | 0.46 in (2019) |
| September 18 | 82.9°F (2009) | 46.0°F (2018) | 0.74 in (2010) |
| September 19 | 87.1°F (1999) | 48.0°F (2013) | 0.38 in (2009) |
| September 20 | 82.0°F (1999) | 46.0°F (2001) | 0.52 in (2008) |
| September 21 | 82.9°F (1999) | 42.1°F (2002) | 0.19 in (2025) |
| September 22 | 86.0°F (1999) | 44.1°F (2000) | 0.44 in (2013) |
| September 23 | 84.0°F (2009) | 39.9°F (2000) | 0.63 in (2014) |
| September 24 | 77.0°F (2006) | 41.0°F (2000) | 0.64 in (2014) |
| September 25 | 80.1°F (2021) | 42.1°F (2000) | 0.48 in (2020) |
| September 26 | 82.9°F (2022) | 43.0°F (2013) | 0.42 in (2011) |
| September 27 | 82.0°F (2003) | 42.1°F (2015) | 0.36 in (2007) |
| September 28 | 88.0°F (2017) | 44.1°F (1999) | 1.66 in (2013) |
| September 29 | 78.1°F (2008) | 43.0°F (2019) | 0.69 in (2013) |
| September 30 | 73.0°F (2020) | 39.9°F (2019) | 1.00 in (2007) |