September weather in Index, WA
The average temperature in Index in September is 59.5°F (48.1°F–70.9°F). Average precipitation: 4.79 inches.
September is a fall month in Index, and is warmer than the annual average of 49.8°F. Daily temperatures swing about 22.8°F between overnight low and afternoon high. Expect about 11 days with precipitation. Daylight averages about 12h 20m. For travel, September is a comfortable month to visit.
Avg High
70.9°F
Avg Low
48.1°F
Precipitation
4.79 in
Daylight
12h 20m
September records in Index
| Date | Record High | Record Low | Record Precip |
|---|---|---|---|
| September 1 | 89.1°F (2022) | 39.9°F (2021) | 2.35 in (2010) |
| September 2 | 98.1°F (1988) | 39.9°F (1984) | 1.56 in (2004) |
| September 3 | 95.0°F (2006) | 37.9°F (2000) | 1.81 in (1994) |
| September 4 | 91.0°F (2003) | 35.1°F (2000) | 0.88 in (1977) |
| September 5 | 90.0°F (2003) | 37.9°F (2000) | 0.97 in (1976) |
| September 6 | 91.0°F (2017) | 35.1°F (2000) | 2.20 in (1985) |
| September 7 | 91.0°F (1981) | 37.9°F (1992) | 1.33 in (2009) |
| September 8 | 91.0°F (2012) | 39.0°F (1983) | 1.93 in (1992) |
| September 9 | 88.0°F (1997) | 37.0°F (1970) | 1.32 in (1982) |
| September 10 | 91.0°F (2020) | 39.0°F (1970) | 2.11 in (1983) |
| September 11 | 90.0°F (2020) | 39.9°F (1972) | 2.08 in (2004) |
| September 12 | 90.0°F (2009) | 35.1°F (1970) | 0.77 in (2003) |
| September 13 | 87.1°F (1979) | 32.0°F (1970) | 0.61 in (1992) |
| September 14 | 90.0°F (1979) | 36.0°F (1971) | 2.94 in (2004) |
| September 15 | 90.0°F (1981) | 36.0°F (2000) | 0.74 in (2019) |
| September 16 | 89.1°F (2014) | 36.0°F (1973) | 0.92 in (2000) |
| September 17 | 86.0°F (2008) | 34.0°F (1971) | 1.60 in (1970) |
| September 18 | 82.0°F (1995) | 37.0°F (1971) | 2.70 in (2021) |
| September 19 | 84.9°F (2009) | 36.0°F (1978) | 1.04 in (1972) |
| September 20 | 87.1°F (1974) | 37.9°F (1993) | 2.30 in (2000) |
| September 21 | 84.9°F (1974) | 37.9°F (2005) | 3.10 in (1972) |
| September 22 | 87.1°F (2014) | 34.0°F (2000) | 2.17 in (1972) |
| September 23 | 90.0°F (2009) | 35.1°F (2005) | 1.99 in (1978) |
| September 24 | 88.0°F (1990) | 32.0°F (1972) | 3.30 in (2020) |
| September 25 | 88.0°F (1991) | 30.0°F (1972) | 1.54 in (2020) |
| September 26 | 80.1°F (1983) | 34.0°F (1972) | 2.85 in (2020) |
| September 27 | 84.0°F (1970) | 34.0°F (1972) | 1.88 in (2011) |
| September 28 | 87.1°F (2003) | 32.0°F (1983) | 1.32 in (2013) |
| September 29 | 88.0°F (2003) | 33.1°F (1972) | 2.84 in (2013) |
| September 30 | 82.0°F (2008) | 30.9°F (2019) | 3.70 in (2005) |