September Weather in San Jose, United States

Last updated: February 24, 2025

In September, San Jose experiences a dynamic weather spectrum, with maximum temperatures soaring to an impressive 41°C (106°F) while maintaining a comfortable average of 19°C (67°F). The evenings can bring a cool respite, dipping to a minimum of 7°C (45°F). Residents and visitors can enjoy nearly uninterrupted sunshine, as the city records only 3 mm (0.1 in) of precipitation, with 0 days of rain throughout the month. With humidity hovering around 55%, the climate remains pleasant, making it an ideal time for outdoor activities and exploration.

September Temperature in San Jose

In September, San Jose experiences a delightful transition as summer begins to wane. With minimum temperatures around 7°C (45°F) and an average of 19°C (67°F), the city enjoys comparatively mild weather. However, the real highlight is the peak temperatures soaring to a sizzling 41°C (106°F), making this month one of the hottest of the year. As the first hints of autumn approach, daytime warmth invites outdoor activities while cooler evenings provide relief, creating a perfect blend of summer's last warmth with the gentle onset of fall. This month stands out not just for its heat but also for the gradual shift towards more temperate conditions, preparing residents for the cooler months ahead.

September Weather in San Jose: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in San Jose, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends.
JanFebMarAprMayJunJulAugSepOctNovDec505153565964666766635550
Data source: Temperature data for San Jose generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

September Precipitation in San Jose

In September, San Jose experiences a notable lull in precipitation, with a mere 3 mm (0.1 in) of rainfall recorded throughout the month. This minimal amount of rainfall is consistent with the summer trend, where July and August see 0 mm of precipitation, resulting in a dry spell that stretches across several months. The transition into autumn, marked by a slight uptick in precipitation in October at 25 mm (1.0 in), signals the onset of the wetter season ahead. Overall, September's dryness is a contributing factor to the region’s striking seasonal variability, as it gears up for the more moisture-laden months that follow.

September Precipitation Trends in San Jose

The chart displays monthly precipitation patterns in San Jose, with values for each month alongside September's data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how September's conditions compare to those of other months.
JanFebMarAprMayJunJulAugSepOctNovDec145133114372410132556116
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in San Jose

As the summer heat fades into autumn, September in San Jose experiences a noticeable shift in humidity levels, dropping to 55%. This marks one of the lowest points of the year, following the dry months of July and August, which boast even lower humidity at 58% and 54%, respectively. However, as the city transitions into October, a gradual increase can be seen with humidity rising to 62%. Overall, September serves as a crucial turning point, where the air becomes crisper and drier, providing a refreshing reprieve before the return of higher humidity levels in late fall and winter. This trend underscores the area's distinct seasonal variations, perfect for those who appreciate the gentler embrace of early autumn.

September Average Humidity in San Jose

This chart illustrates the average monthly humidity levels in San Jose, with September's data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, allowing you to see how September's humidity levels compare to other months.
JanFebMarAprMayJunJulAugSepOctNovDec82%84%82%78%71%64%59%54%55%62%78%80%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in San Jose

As the summer wanes and September arrives in San Jose, residents can expect a very high UV Index of 9, along with a reduced burn time of 15 minutes. This marks a slight decrease from the intense, extreme conditions of the preceding months, reflecting the gradual transition from peak sunlight exposure. Following the extreme levels of UV Index 11 recorded in May through July, September brings a welcome reprieve, yet the caution remains; protective measures are still essential to avoid skin damage. As autumn begins to creep in, the UV levels will further decline in October, but for now, vigilance is key for outdoor enthusiasts. For more detailed information, check out the San Jose UV Index.

Maximum UV Index Levels in San Jose for September

The chart shows the monthly maximum UV Index (UVI) for San Jose in September, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues.
JanFebMarAprMayJunJulAugSepOctNovDec4589111111109753
Data source: San Jose September UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

September Sunshine in San Jose

As summer gently yields to autumn, September in San Jose shines brightly with 310 hours of sunlight, marking a charming transition from the peak summer months. After basking in an impressive 379 hours in July, the days begin to shorten, but the warmth lingers, with September still boasting a generous amount of sun. This month's sunlight is a delightfully vibrant contrast to the earlier winter months, showcasing a gradual decline in brightness as the year shifts—swinging from 360 hours in May to 206 hours in December. In essence, September encapsulates the essence of summer's warmth while hinting at the cool embrace of fall, offering a perfect backdrop for outdoor activities and community events.

Monthly Sunshine Duration in San Jose: September Highlighted

The September sunshine duration represents the total number of hours San Jose experiences direct sunlight during the month of September, excluding cloudy or obstructed periods. This chart compares the sunshine duration of September with the other months of the year.
JanFebMarAprMayJunJulAugSepOctNovDec162h222h269h303h360h373h379h348h310h286h233h206h
Data source: San Jose September Sunshine duration data generated using information from the Copernicus Climate Change Service.

Chance of Sun in San Jose During September

In San Jose, September marks a delightful transition into autumn, boasting a sunny weather likelihood of 80%. This places it just below the peak summer months, where August enjoys an impressive 84% chance of sunshine. As summer fades, the consistent warmth remains, making September a fantastic time for outdoor activities under the clear blue skies. The likelihood of sunshine dips slightly in the following months, with October falling to 58%, so it's a prime opportunity to soak in the last rays of summer before the cooler, cloudier days set in. Overall, September provides a perfect blend of warmth and brightness, ideal for both residents and visitors alike.

Percentage of Sunny Days in September in San Jose

The chart illustrates the percentage of sunny days in San Jose throughout the year, with September highlighted. It highlights the variation in sunshine across each month and provides an overview of the typical frequency of sunny days, offering insights into how often San Jose experiences clear skies throughout the year.
JanFebMarAprMayJunJulAugSepOctNovDec44%57%56%56%75%74%75%84%80%58%55%40%
Data source: San Jose September chance of sun data, generated using information from the Copernicus Climate Change Service.

Daylight Hours in San Jose in September

As September arrives in San Jose, the warmth of summer begins to wane, reflected in the gradual decrease of daylight to 12 hours. This month's daylight marks a subtle transition; following the peak of 14 hours experienced during the summer months of June through August, September ushers in shorter days while still retaining a generous amount of sunlight. The trend is clear: as the year progresses from January's 9 hours of daylight, daylight hours steadily increase until they reach their zenith in summer, only to gradually taper off again, leading into the cozy, shorter days of fall and winter. This cyclical dance of daylight offers residents a beautiful blend of sun-soaked days and enchanting evenings as they transition into autumn.

Average Daylight Hours in San Jose for September

The chart illustrates the variation in daylight duration in San Jose throughout the year, with September highlighted. It shows the monthly changes in daylight hours, calculated by summing the hours between sunrise and sunset.
JanFebMarAprMayJunJulAugSepOctNovDec9h 55m10h 49m11h 59m13h 10m14h 10m14h 39m14h 23m13h 30m12h 21m11h 10m10h 9m9h 38m
Data source: San Jose daylight hours, calculated by summing the hours between sunrise and sunset for each day.

September Winds in San Jose

As summer gracefully fades into autumn, September in San Jose experiences a gentle shift in its breezy character, with average wind speeds settling at 1.6 m/s (4 mph). While this is a slight increase from the lowest points of July and August, it marks a stable and tranquil period, reminiscent of the calm before the seasonal change. Notably, the wind patterns remain consistent throughout the year, generally hovering around 2.1 m/s to 2.2 m/s during the cooler months, while the summer months bring quieter breezes. This steady wind backdrop in September enhances the region's charm, inviting residents and visitors alike to relish in the mild, refreshing air as the vibrant colors of fall begin to emerge.

Average September Wind Speed in San Jose

The chart displays monthly wind speed patterns in San Jose, with values for each month shown alongside September's data, which is highlighted for easy comparison. It illustrates the average wind speed, offering insights into how September's wind conditions compare to the rest of the year.
JanFebMarAprMayJunJulAugSepOctNovDec2.12.22.11.92.22.11.61.51.6 m/s2.11.72.2
Data source: San Jose September wind data, generated using information from the Copernicus Climate Change Service.

How September Weather in San Jose Compares to Other Months

The weather in San Jose 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 San Jose and find detailed weather information for every month.

September and January present contrasting weather patterns. September boasts a broader temperature range, with minimums around 7°C (45°F) and maximums soaring to 41°C (106°F), coupled with minimal precipitation of just 3 mm (0.1 in) and no rainy days, resulting in a moderate humidity level of 55%. In stark contrast, January sees cooler temperatures, with minimums dropping to 0°C (32°F) and average highs around 24°C (75°F). The month is significantly wetter, receiving 145 mm (5.7 in) of rainfall over 8 days, and experiences higher humidity at 82%. For additional insights on January weather, visit San Jose weather in January.

September weather is characterized by a mild average temperature of 19°C (67°F) and can peak at a scorching 41°C (106°F), with very little precipitation, registering at only 3 mm (0.1 in) throughout the month. In contrast, February experiences much cooler temperatures, with an average of 11°C (52°F) and a minimum of -1°C (30°F), along with significantly higher precipitation levels of 133 mm (5.2 in) spread over 8 days, contributing to an increased humidity of 84%. This stark difference highlights the transition from the dry heat of early fall to the wetter and cooler conditions typical of winter. For more details, you can check out San Jose weather in February.

September and March exhibit stark contrasts in weather patterns. September enjoys warmer temperatures, with averages around 19°C (67°F) and maximums soaring up to 41°C (106°F), while March is cooler, averaging only 11°C (53°F) and peaking at 26°C (79°F). Additionally, September experiences minimal precipitation, averaging just 3 mm (0.1 in) over no rainy days, whereas March is significantly wetter, receiving 114 mm (4.5 in) of rain across 12 days. Humidity is also higher in March at 82% compared to September's 55%, highlighting the more comfortable and drier conditions of early autumn. For more detailed insights, check out San Jose weather in March.

In comparing the weather between September and April, September generally offers much warmer temperatures, with an average high of 41°C (106°F), while April sees a milder average high of 31°C (88°F). Precipitation is minimal in September, with only 3 mm (0.1 in) and no rainy days, contrasting sharply with April's wetter climate, which experiences 37 mm (1.4 in) of rain over four days. Additionally, September has a lower humidity level at 55%, whereas April's humidity is notably higher at 78%, contributing to a more humid experience during the spring month. For more detailed information, you can check San Jose weather in April.

In comparing the weather of September and May, September tends to present a warmer climate with an average temperature of 19°C (67°F) and maximums reaching up to 41°C (106°F), while May is cooler with an average of 15°C (59°F) and max temperatures of 32°C (90°F). Additionally, September is characterized by very low precipitation, recording only 3 mm over the month, and notably no rainy days, in contrast to May, which experiences around 24 mm of rain over two days. Humidity levels also differ, as September sits at a moderate 55%, while May has a higher humidity at 71%. For a more detailed look at May weather, you can check San Jose weather in May.

In comparing the weather of September and June, we find that both months exhibit relatively mild temperatures, but with some distinct differences. September features a minimum temperature of 7°C (45°F) and an average of 19°C (67°F), reaching up to 41°C (106°F) at its peak. In contrast, June starts slightly warmer with a minimum of 8°C (47°F) and averages 18°C (64°F), with a maximum temperature of 37°C (99°F). Precipitation is minimal in both months—September records just 3 mm (0.1 in) while June has a negligible 1 mm (0.0 in)—indicating dry weather throughout. Humidity levels are also noteworthy, with September averaging 55% compared to June's higher 64%, reflecting a more comfortable feel in September. For more detailed insights into the climate, check out San Jose weather in June.

In comparing the weather between September and July, both months exhibit average temperatures around 19°C (66°F), but their extremes differ significantly. September sees a remarkable maximum temperature of 41°C (106°F), contrasting with July's high of 34°C (93°F). Moreover, September experiences minimal precipitation with only 3 mm recorded, while July has no rain at all, making both months quite dry, with July maintaining slightly higher humidity at 58% compared to September's 55%. For more detailed information on July weather, check out San Jose weather in July.

September's weather sees a slight decrease in minimum temperatures compared to August, dropping from 11°C (52°F) to 7°C (45°F). However, the average temperature remains steady at 19°C (67°F) for both months. Notably, September experiences higher maximum temperatures, reaching up to 41°C (106°F) compared to August's maximum of 39°C (102°F). Both months are dry, with September receiving only 3 mm of precipitation over 0 days, while August remains completely dry with 0 mm of rain. Humidity levels are also comparable, with September at 55% and August slightly lower at 54%. For more information, you can check San Jose weather in August.

September sees a wider range of temperatures, with minimums at 7°C (45°F) and maximums peaking at a high of 41°C (106°F), while maintaining a warm average of 19°C (67°F). Notably, September experiences minimal precipitation and lower humidity levels at 55%. In contrast, October brings cooler temperatures, with minimums dropping to 5°C (42°F) and an average of 17°C (63°F), peaking at a maximum of 34°C (94°F). The month also sees a significant increase in precipitation, totaling 25 mm (1.0 in) over just one day, and humidity rises to 62%. For more details on what to expect, check out San Jose weather in October.

September typically experiences warmer temperatures compared to November, with an average of 19°C (67°F) and peak highs reaching up to 41°C (106°F). In contrast, November's average temperature drops to 13°C (56°F), with maximums around 28°C (83°F). While September boasts very little precipitation—only 3 mm over none of the month’s days—November sees a significant increase in rainfall at 56 mm over five days. Additionally, humidity levels rise from 55% in September to 78% in November, contributing to a cooler, more damp atmosphere. For more specific details on November weather, visit San Jose weather in November.

September and December in San Jose present stark contrasts in weather conditions. September typically enjoys a warm climate with average temperatures around 19°C (67°F) and occasional peaks up to 41°C (106°F), yet it experiences very little precipitation, with just 3 mm recorded over the entire month. In contrast, December sees cooler temperatures, averaging 10°C (50°F), with a maximum of 24°C (76°F) and a minimum of 1°C (34°F). This month is notably wetter, with 116 mm of rain spread over approximately nine days, contributing to higher humidity levels around 80%. For more detailed information, you can check San Jose weather in December.

Compare San Jose's Climate with Cities Worldwide

Conclusion: What to Expect From September Weather in San Jose

As summer transitions into fall, September is marked by balmy temperatures and surprisingly dry conditions in San Jose. With average highs reaching a comfortable 19°C, this month is a welcome change from the sweltering heat often experienced in the peak of summer. Unlike other months that may bring more precipitation, September stands out with minimal rainfall, allowing residents and visitors alike to enjoy outdoor activities under mostly clear skies. The 55% humidity adds a pleasant warmth without feeling overly muggy, making it an ideal time to explore the vibrant surroundings. For more insights on what to expect throughout the year, check out San Jose Climate.