Napa, CA weather in September
Expect warm, dry weather in Napa in September, with highs near 84°F and lows near 53°F. Rain falls on about 1 day. It is one of the warmest months in Napa. Good for outdoor plans.
- Normal high
- 84°F
- Normal low
- 53°F
- Wet days
- 1
- 0.09 in total
- Muggy days
- 0
- dew point 65°F+
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 85°F | 83°F |
| Normal low | 55°F | 52°F |
| Chance of a wet day | 2% | 6% |
| Sunrise / sunset | 6:38 am / 7:39 pm | 7:04 am / 6:54 pm |
| Daylight | 13.0 h | 11.8 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Pacific Time).
A typical September day
- 6 am57°Fdew point 51°F
- 9 am70°Fdew point 51°F
- Noon81°Fdew point 50°F
- 3 pm85°Fdew point 48°F
- 6 pm76°Fdew point 50°F
- 9 pm65°Fdew point 51°F
NOAA hourly normals (local standard time) from Travis AFB (19 mi away); average wind 14 mph; clear or few clouds in 87% of daytime hours, mostly cloudy or overcast in 7%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F11 of 30
- Hot dayshigh 90°F or more8 of 30
- Muggy daysdaily mean dew point 65°F or more0 of 30
- Wet daysat least 0.01 in of rain or melted snow1 of 30
- Notable rainat least 0.10 in0 of 30
- Freezing nightslow 32°F or below0 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain in September
Normal precipitation is 0.09 in; a dry September brings about 0.0 in and a wet one about 0.1 in (25th and 75th percentiles). Days with half an inch or more are rare.
How September varies from year to year
- Warmest September, 1991-20202020: average high 90°F
- Coolest September2005: average high 79°F
- Wettest September2013: 0.7 in
- Driest September1992: no measurable precipitation
- Highest reading111°F (September 7, 2020)
- Lowest reading42°F (September 29, 2007)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
September compared with August and October
| August | September | October | |
|---|---|---|---|
| Normal high | 84°F | 84°F | 78°F |
| Normal low | 56°F | 53°F | 49°F |
| Wet days | 0 | 1 | 4 |
| Comfortable days | 13 | 11 | 17 |
| Daylight | 13.6 h | 12.4 h | 11.2 h |
Highs change by 0°F from August and -6°F into October.
Nearby alternatives in September
- Warmer: Stockton, CA59 mi · high 90°F · 1 wet day
- Cooler: San Francisco, CA37 mi · high 70°F · 1 wet day
How Napa ranks in September
- Normal high139th warmest of 378 cities; 31st of 60 in California
- Wet days47th driest of 378
- Comfortable days145th most of 342
What to pack for Napa in September
- Layers – afternoons near 84°F but nights near 53°F
Heating and cooling
September has 14 heating degree days and 131 cooling degree days (base 65°F), 5% of the year's total heating and cooling demand.
Questions
How hot is Napa in September?
The normal high is 84°F and the normal low is 53°F. From 1991 to 2020 the hottest September reading was 111°F (September 7, 2020).
Does it rain a lot in Napa in September?
About 1 days in September have at least 0.01 in of precipitation, and the normal total is 0.09 in. The wettest September in 1991-2020 was in 2013 (0.7 in); the driest was in 1992, with no measurable precipitation.
Is September a good time to visit Napa?
September ranks 9th of 12 months on our comfort score for Napa (62 out of 100). It has about 11 comfortable days and about 8 days at 90°F or hotter. The best month is May.
Where the numbers come from
- Temperature, rain, snowfall and frost dates: Napa State Hospital (USC00046074), 1.8 mi SE of the city center, 35 ft . NOAA normals and daily records, 1991-2020.
- Snow depth: Fairfield (USC00042934), 12 mi E of the city center, 40 ft . NOAA normals and daily records, 1991-2020.
- Humidity and wind by hour and cloud cover: Travis AFB (USW00023202), 19 mi E of the city center, 59 ft . NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: Napa County Airport (724955-93227), 6.2 mi S of the city center, 15 ft . Hourly observations, 1991-2020.