Last updated: February 24, 2025
In September, Napa, United States, experiences a warm climate, with maximum temperatures reaching an impressive 44°C (111°F), while the average temperature settles around a comfortable 21°C (70°F). Nights bring a refreshing change, dipping to a minimum of 8°C (46°F). The month boasts minimal precipitation, with just 1 mm (0.0 in) of rain recorded and no precipitation days, making it ideal for outdoor activities. Furthermore, the humidity level stands at a moderate 44%, ensuring a pleasant atmosphere throughout the month.
As September unfolds in Napa, United States, the temperatures offer a sublime transition into the fall season. With minimums dropping to 8°C (46°F) and averages settling pleasantly at 21°C (70°F), the air carries a refreshing crispness reminiscent of autumn's approach. **Peaking at a striking 44°C (111°F), September still holds onto the summer warmth, marking the last stronghold of high temperatures before cooler months set in. This blend of warmth and mildness creates an inviting atmosphere perfect for vineyard exploration and outdoor activities, making Napa a delightful destination in this beautiful month. The steady decline in minimum temperatures from the scorching highs of summer signals a slow but certain transition to the cozy charm of fall.
September in Napa sees a notable decline in precipitation, with a mere 1 mm (0.0 in) recorded, reflecting the region's characteristic dry spell as summer transitions into fall. This month stands out, not just for its low rainfall but also for a complete absence of rainy days, marking a stark contrast to the wetter months at the beginning of the year. Traditionally, January and February dominate with over 100 mm of rainfall and several rainy days, while September wraps up the dry season, paving the way for the moderate precipitation that typically occurs in the following months. This trend highlights Napa's climate patterns, where late summer yields to the promise of autumn rains, setting the stage for the region’s renowned vineyards to flourish.
In Napa, September marks a notable transition in humidity levels, dipping to 44%, reminiscent of the drier months of July and August. This decrease from a humid summer creates a refreshing environment for both locals and visitors, allowing vineyards to flourish as the season shifts. By this time of year, the air feels lighter and clearer, offering a stark contrast to the dampness of early winter months, where humidity peaks again at 84% in November and January. As the days shorten and temperatures cool, September stands out as a bridge between the warm, arid summer and the wetter seasons ahead, enticing everyone to enjoy the crispness of early autumn in this beautiful region.
In September, Napa experiences a UV Index of 9, indicating a very high exposure level. As summer transitions into fall, the UV intensity begins to decline from the extreme highs of July and June, yet caution is still essential, with a burn time of just 15 minutes for unprotected skin. Compared to the earlier months, the UV Index shows a trend of gradual decrease, having peaked at 11 in both June and July. This September reading aligns closely with April's intensity, emphasizing the importance of sun protection as outdoor activities continue in the Pleasant Californian weather. For those looking to enjoy the sunshine safely, it’s a good reminder to check the daily UV levels, especially in such sunny locales. For more details, visit Napa UV Index.
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As summer gently transitions to fall, September in Napa bathes in a delightful 314 hours of sunshine. This sunny month marks a peak in daylight, following July's impressive 394 hours, and forms a vivid backdrop to the vibrant vineyards and picturesque landscapes for which the region is renowned. Although the sunlight begins to taper off into October, bringing 280 hours, September remains a splendid time to enjoy the rich harvest season. This gradual decline from the summer highs reflects the changing seasons, offering a uniquely beautiful charm that draws both locals and visitors to embrace the warmth of the sun while savoring the anticipation of autumn's bounty.
As summer transitions into fall, Napa, United States, experiences a delightful likelihood of sunny weather in September, boasting a 76% chance of sun. This trend reflects a gradual decline from the peak sunshine of May and June, which enjoy an impressive 82% chance. While the weather remains predominantly sunny, September’s figures indicate a slight dip compared to the earlier months of the summer season. Overall, this month is still favorable for outdoor activities and wine tasting, making it an appealing time to visit as the vineyards begin to showcase their autumnal beauty.
As September rolls into Napa, the daylight duration begins to gradually wane, offering a delicate transition from the bright, sun-soaked months of summer. With approximately 12 hours of daylight, this month marks a subtle shift, down from June, July, and August's peak of 14 hours. The daylight hours continue to lessen as autumn approaches, reflecting a steady decline throughout the year—starting with 9 hours in January and reaching 11 hours in October. This gradual ebb of sunlight not only signals the changing season but also invites an appreciation for the warm, golden hues that define Napa's vibrant landscapes during this time. As days shorten, the promise of cozy evenings and harvest celebrations draws near, making September a perfect bridge between summer's vibrance and fall's embrace.
As summer transitions into autumn, September in Napa ushers in a gentler breeze, with average wind speeds dropping to 2.4 m/s (5 mph)—a slight decline from the warm summer months. Following a peak during May and June, where winds freshened to 3.1 m/s (7 mph) and 3.3 m/s (7 mph), the softer gusts of September create a serene atmosphere, perfect for vineyard strolls and outdoor festivities. This calming trend continues into October, suggesting a gradual winding down of the season's energy. With November bringing the slowest winds at 1.6 m/s (4 mph), Napa’s landscape showcases a graceful shift, inviting locals and visitors alike to relish in the mild, tranquil beauty of early autumn.
The weather in Napa changes throughout the year, offering a unique experience in each season. Below is a month-by-month comparison of September's weather with other months, highlighting differences in temperature, precipitation, and other key factors. Click on each section to discover seasonal trends in Napa and find detailed weather information for every month.
September's weather boasts mild to warm temperatures, ranging from a minimum of 8°C (46°F) to a scorching maximum of 44°C (111°F), with an average temperature of 21°C (70°F). With barely any precipitation and low humidity at 44%, it's a relatively dry month. In stark contrast, January features much cooler temperatures, with a minimum of -2°C (29°F) and a maximum of 25°C (77°F), averaging around 10°C (50°F). This month also sees significant rainfall, totaling 119 mm (4.7 in) over approximately eight days, coupled with higher humidity at 84%. For more insights on the January weather in Napa, you can check this link: Napa weather in January.
September and February present striking contrasts in weather conditions. In September, temperatures can soar to a maximum of 44°C (111°F), although the average remains a more moderate 21°C (70°F), with minimal precipitation and low humidity at 44%. In stark contrast, February features much cooler temperatures, with a minimum of -1°C (30°F) and an average of only 11°C (53°F). This month experiences significantly more precipitation, totaling 113 mm (4.5 in) over approximately 7 days, and the humidity rises to 84%. For a closer look at February weather specifics, you can check Napa weather in February.
September and March present stark contrasts in weather conditions. In September, temperatures range from a mild 8°C (46°F) to a scorching 44°C (111°F), with an average of 21°C (70°F) and virtually no precipitation, making it a dry month with humidity at 44%. In contrast, March experiences cooler temperatures, with a minimum of 1°C (34°F) and a maximum of 30°C (87°F), averaging around 12°C (55°F). Additionally, March sees substantial rainfall of 81 mm (3.2 in) over 9 days and higher humidity levels at 83%. For more details on March weather, check out Napa weather in March.
September and April present markedly different weather patterns. In September, temperatures range from a cooler minimum of 8°C (46°F) to a sweltering maximum of 44°C (111°F), with an average of 21°C (70°F). The month boasts little to no rainfall, with only 1 mm recorded and a low humidity level of 44%. In contrast, April features milder temperatures, with a minimum of 3°C (38°F) and a maximum of 33°C (92°F), averaging around 15°C (60°F). This month experiences a significant amount of precipitation, totaling 33 mm over 5 days, alongside a substantially higher humidity of 81%. For more details on the April weather specifics, check out Napa weather in April.
In September, the weather typically showcases a wide range of temperatures, featuring a minimum of 8°C (46°F), an average of 21°C (70°F), and a maximum that can soar up to 44°C (111°F). With minimal precipitation at just 1 mm (0.0 in) and no rainy days, the humidity is relatively low at 44%. In contrast, May tends to be cooler, with temperatures ranging from a minimum of 5°C (41°F) to an average of 18°C (64°F), and a maximum of 37°C (99°F). The month is characterized by more humidity at 74% and a higher precipitation level of 19 mm (0.8 in) over 2 days, indicating a more variable weather pattern. For more detailed insights, check out Napa weather in May.
In comparing the weather of September and June, both months exhibit similar average temperatures around 21°C (70°F), but their extremes highlight notable differences. September can reach a staggering maximum of 44°C (111°F), while June's peak is slightly lower at 41°C (106°F). The minimum temperatures are also similar, with September starting at 8°C (46°F) and June slightly warmer at 10°C (51°F). Additionally, June experiences a higher humidity level at 64%, compared to September's 44%, contributing to a more comfortable climate. Precipitation levels are minimal in both months, with June recording 2 mm (0.1 in) and September just 1 mm (0.0 in). For more detailed insights, check out Napa weather in June.
In comparison of weather between September and July, both months share a similar average temperature of 21°C (70°F) and humidity levels at 44%. However, September offers a broader range of temperatures, with minimums dipping to as low as 8°C (46°F) and maximums peaking at 44°C (111°F). In contrast, July presents a milder temperature spectrum with minimums at 11°C (53°F) and a slightly lower maximum of 40°C (104°F). Notably, both months experience minimal precipitation, with September recording just 1 mm and July remaining completely dry. For more details about July's weather, visit Napa weather in July.
In comparing the weather of September and August, September shows a slight edge in temperature variability with a minimum of 8°C (46°F) and a maximum of 44°C (111°F), while August has a minimum of 12°C (53°F) and a maximum of 42°C (108°F). Despite both months experiencing minimal precipitation—September recording only 1 mm and August none at all—they differ in humidity levels; September's humidity is slightly higher at 44% compared to August's 36%. Overall, while both months maintain a warm average temperature around 21°C (70°F for September and 71°F for August), September offers broader temperature extremes. For a deeper look at August's weather, you can visit Napa weather in August.
In September, the weather features a greater temperature range, with minimums around 8°C (46°F) and highs soaring up to 44°C (111°F), resulting in an average temperature of 21°C (70°F). Additionally, the month is remarkably dry, with only 1 mm of precipitation and low humidity at 44%. In contrast, October sees cooler temperatures, with minimums dropping to 4°C (40°F) and an average of 18°C (65°F), while maximums reach a more moderate 36°C (98°F). October also experiences a notable increase in precipitation, totaling 29 mm (1.1 in) over two days, and humidity rises to 65%. For more specific details on October weather, check out Napa weather in October.
September generally offers much warmer temperatures, with a minimum of 8°C (46°F) and an average high of 44°C (111°F), while November sees a significant drop, reaching a minimum of 0°C (32°F) and an average high of 30°C (86°F). Additionally, September is characterized by dry conditions and low humidity at 44%, in stark contrast to November’s increased humidity of 84% and a higher precipitation level of 43 mm (1.7 in) over five days. For a more detailed look at the weather patterns, visit Napa weather in November.
September and December present starkly contrasting weather conditions. In September, temperatures range from a pleasant minimum of 8°C (46°F) to a scorching maximum of 44°C (111°F), with an average of 21°C (70°F) and virtually no precipitation, displaying a dry humidity level of 44%. In contrast, December sees much cooler temperatures, with a minimum of 0°C (32°F) and a maximum of 24°C (75°F), averaging just 10°C (50°F). This month is significantly wetter, experiencing 91 mm (3.6 in) of rainfall over nine days, coupled with a higher humidity of 83%. For more details on the December climate, you can visit Napa weather in December.
As we wrap up our exploration of Napa's September weather, it's clear that this month stands out with its warm temperatures and remarkably dry conditions. With an average temperature of 21°C (70°F), September enjoys a pleasant warmth that is perfect for outdoor activities, while the lack of precipitation—zero days of rain ensuring outdoor plans go uninterrupted—makes it distinctly different from the wetter months. The 44% humidity adds to the comfort, making it an ideal time to enjoy Napa's renowned vineyards and picturesque landscapes. For a deeper dive into Napa's unique climate patterns throughout the year, visit Napa Climate.