Napa County Weather in September
Average highs run from 89°F on September 1 to 84°F on September 30, and lows from 55°F to 52°F. Normal precipitation for the month is 0.06 in over about 1 wet days.
September day by day
The normal high and low for each date, and the record, in °F.
- Normal low
- Normal high
- Record high
- Record low
September at a glance
- Average high
- 87°F
- Average low
- 54°F
- Precipitation
- 0.06 in
- Record high
- 115°FSep 6, 2022
- Record low
- 35°FSep 29, 2019
- Chance of a freeze
- 0%
- Days of 90°F or more
- 10.4
- Daylight
- 13 h 00 min to 11 h 49 min
- Cloud cover
- 26%
- Humidity
- 47%
- Dew point
- 43°F
- Wind
- 6.5 mph
Every day of the month
A wet day has at least 0.01 inch of precipitation.
| Date | Normal high | Normal low | Record high | Record low | Chance wet |
|---|---|---|---|---|---|
| Sep 1 | 89°F | 55°F | 106°F 2017 | 45°F 1999 | 1% |
| Sep 2 | 89°F | 55°F | 107°F 2017 | 46°F 2004 | 1% |
| Sep 3 | 89°F | 55°F | 96°F 2008 | 44°F 2000 | 1% |
| Sep 4 | 89°F | 55°F | 100°F 2004 | 43°F 2000 | 1% |
| Sep 5 | 88°F | 55°F | 111°F 2022 | 44°F 2000 | 1% |
| Sep 6 | 88°F | 55°F | 115°F 2022 | 42°F 2015 | 1% |
| Sep 7 | 88°F | 55°F | 106°F 2020 | 39°F 2002 | 1% |
| Sep 8 | 88°F | 55°F | 103°F 2022 | 43°F 2002 | 1% |
| Sep 9 | 88°F | 55°F | 99°F 2015 | 43°F 2002 | 2% |
| Sep 10 | 88°F | 55°F | 96°F 2017 | 40°F 2005 | 2% |
| Sep 11 | 88°F | 54°F | 98°F 2017 | 40°F 2005 | 2% |
| Sep 12 | 88°F | 54°F | 99°F 2003 | 40°F 2005 | 2% |
| Sep 13 | 87°F | 54°F | 100°F 2003 | 46°F 2002 | 2% |
| Sep 14 | 87°F | 54°F | 89°F 2004 | 45°F 2018 | 2% |
| Sep 15 | 87°F | 54°F | 91°F 2004 | 39°F 2006 | 2% |
| Sep 16 | 87°F | 54°F | 87°F 2025 | 38°F 2006 | 2% |
| Sep 17 | 87°F | 54°F | 94°F 2000 | 42°F 2005 | 2% |
| Sep 18 | 86°F | 54°F | 98°F 2016 | 38°F 2008 | 3% |
| Sep 19 | 86°F | 54°F | 97°F 2002 | 41°F 2005 | 3% |
| Sep 20 | 86°F | 53°F | 97°F 2011 | 38°F 2004 | 3% |
| Sep 21 | 86°F | 53°F | 102°F 2003 | 41°F 2012 | 3% |
| Sep 22 | 86°F | 53°F | 99°F 2003 | 39°F 2017 | 3% |
| Sep 23 | 85°F | 53°F | 96°F 2025 | 39°F 2005 | 3% |
| Sep 24 | 85°F | 53°F | 96°F 2019 | 40°F 2005 | 4% |
| Sep 25 | 85°F | 53°F | 99°F 2016 | 37°F 2005 | 4% |
| Sep 26 | 85°F | 53°F | 99°F 2009 | 43°F 2013 | 4% |
| Sep 27 | 84°F | 53°F | 101°F 2020 | 45°F 2004 | 4% |
| Sep 28 | 84°F | 52°F | 103°F 2020 | 40°F 2001 | 4% |
| Sep 29 | 84°F | 52°F | 96°F 1999 | 35°F 2019 | 5% |
| Sep 30 | 84°F | 52°F | 98°F 2001 | 37°F 2009 | 5% |
Chance of rain
- Chance of a wet day
Sunrise and sunset
Times for 2026, local time (PDT).
- September 1
- sunrise 6:39 AM, sunset 7:39 PM
- September 30
- sunrise 7:04 AM, sunset 6:53 PM
Other months
Sources
Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USC00047643 (Saint Helena), public domain. Records: NOAA GHCN-Daily, station USW00093227, every year on file, quality-flagged values removed. Cloud, humidity, wind and sunshine: NASA POWER (MERRA-2, CERES and GEWEX SRB), 1991-2020. The data was obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division: POWER Daily API v2, accessed 2026-09-24. Sun and moon: computed with the NOAA solar equations and Meeus.