Monthly climate guide
Napa weather in September
Expect hot weather in Napa in September: afternoons reach about 31°C (87°F), while nights drop to around 14°C (57°F). Around 4 mm of rain falls over the month (very dry), and skies are mostly sunny. Daytime highs are about the same as August and 5°C warmer than October.
What stands out in September
- Expect a big gap between day and night — about 17°C.
- Napa is usually about 6°C warmer than San Francisco, 60 km away, in September.
- September is Napa's third warmest month.
- It's one of the drier months, with about 92% less rain than Napa's average.
Avg high
31°C
87°F
Avg low
14°C
57°F
Rainfall
4 mm
very dry
Humidity
48%
relative
Sky
22%
cloud · mostly sunny
Napa weather by month
Show the monthly averages as a table
| Month | Avg high | Avg low | Rain | Humidity | Cloud cover |
|---|---|---|---|---|---|
| January | 14°C / 56°F | 4°C / 39°F | 116 mm | 83% | 55% |
| February | 15°C / 58°F | 4°C / 40°F | 114 mm | 79% | 47% |
| March | 16°C / 61°F | 6°C / 42°F | 119 mm | 81% | 55% |
| April | 19°C / 67°F | 7°C / 45°F | 39 mm | 75% | 44% |
| May | 23°C / 74°F | 9°C / 48°F | 18 mm | 68% | 37% |
| June | 29°C / 85°F | 12°C / 54°F | 8 mm | 54% | 22% |
| July | 32°C / 89°F | 14°C / 56°F | 0 mm | 48% | 19% |
| August | 32°C / 90°F | 14°C / 57°F | 0 mm | 49% | 24% |
| September | 31°C / 87°F | 14°C / 57°F | 4 mm | 48% | 22% |
| October | 26°C / 79°F | 11°C / 52°F | 27 mm | 52% | 29% |
| November | 18°C / 65°F | 7°C / 44°F | 71 mm | 68% | 43% |
| December | 13°C / 56°F | 4°C / 39°F | 114 mm | 78% | 49% |
What to pack for September
- Light, breathable clothing (cotton or linen)
- A sun hat and high-SPF sunscreen
- A refillable water bottle
- An extra layer — evenings are noticeably cooler than afternoons
- Sunglasses
Is September a good time to visit Napa?
Compare the months in the chart above to find your ideal window.
Best time to visit Napa →Other United States cities in September
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Napa weather in September. WeatherCompare, 2026 (NASA POWER / ERA5, 2011–2020 monthly averages). https://weathercompare.eu/weather/usa/napa/september
<a href="https://weathercompare.eu/weather/usa/napa/september">Napa weather in September</a> (WeatherCompare)
<iframe src="https://weathercompare.eu/embed/usa/napa" width="300" height="160" style="border:0;border-radius:12px" loading="lazy" title="Napa weather in September"></iframe> <p style="font-size:12px"><a href="https://weathercompare.eu/weather/usa/napa/september">Napa weather in September</a> – WeatherCompare</p>
Napa in September: quick answers
Is September a good time to visit Napa?
September is a reasonable time for Napa: highs around 31°C and about 4 mm of rain, though not one of the three best months.
How warm is Napa in September?
Average highs are about 31°C (87°F) and average lows about 14°C (57°F), based on 10 years of daily data.
Does it rain a lot in Napa in September?
Napa typically gets around 4 mm of rain in September — very dry.
Figures are long-term averages for the area around Napa (NASA POWER / ERA5, 2011–2020), not a forecast for a specific year. For upcoming days, see the live multi-source forecast.