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September Weather in San Jose, United States

Last updated: June 24, 2025

In San Jose, United States, the average temperature in September hovers around 26°C (79°F), offering a pleasant climate for outdoor activities. However, temperatures can vary significantly, dipping to a chilly 13°C (55°F) at night and soaring to a sweltering 39°C (102°F) during the day. Expect about 28 mm (1.1 in) of precipitation over 4 days, accompanied by an average humidity of 66%, creating a warm yet comfortable atmosphere.

September Temperature in San Jose

In September in San Jose, the average temperature is 26°C (79°F). Maximums can reach 39°C (102°F), while minimums can drop as low as 13°C (55°F). Travelers should prepare for warm days and cooler evenings during this time.

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. In San Jose, September typically has an average temperature of 26°C (79°F), with highs reaching up to 39°C (102°F) and lows dropping to around 13°C (55°F).
JanFebMarAprMayJunJulAugSepOctNovDec465058687686868579685848
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 San Jose in September, the precipitation amount is 28 mm (1.1 in) over the course of 4 days.

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. In San Jose, September typically receives around 28 mm (1.1 inches) of precipitation spread over approximately 4 days.
JanFebMarAprMayJunJulAugSepOctNovDec233216234452228132025
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in San Jose

In San Jose in September, humidity is 66%. With an average temperature of 26°C (79°F), this humidity feels like a warm, enveloping blanket, making outdoor activities invigorating yet requiring occasional breaks in the shade to stay comfortable while traveling.

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, helping you understand how conditions vary by season. In September, average humidity in San Jose is approximately 66%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec81%82%68%55%45%37%43%53%66%72%81%84%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in San Jose

In San Jose in September, the maximum UV index reaches 11, which corresponds to an extreme Exposure Category. With a time to burn of just 10 minutes, it's essential to take precautions. For more details, you can check the Hourly UV Index in San Jose.

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. In September, the maximum UV index in San Jose typically reaches 11, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec5710111212121211864
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.

How September Weather in San Jose Compares to Other Months

Weather in San Jose varies notably across the year, with each month offering distinct climate conditions. This page compares September’s weather to other months in San Jose, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in San Jose, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather8°C (47°F)23 mm (0.9 inches)81%moderate
February Weather10°C (50°F)32 mm (1.2 inches)82%high
March Weather15°C (59°F)16 mm (0.6 inches)68%very high
April Weather20°C (68°F)2 mm (0.1 inches)55%extreme
May Weather24°C (76°F)3 mm (0.1 inches)45%extreme
June Weather30°C (86°F)4 mm (0.2 inches)37%extreme
July Weather30°C (86°F)45 mm (1.8 inches)43%extreme
August Weather29°C (85°F)22 mm (0.9 inches)53%extreme
September Weather26°C (79°F)28 mm (1.1 inches)66%extreme
October Weather20°C (68°F)13 mm (0.5 inches)72%very high
November Weather14°C (58°F)20 mm (0.8 inches)81%high
December Weather9°C (48°F)25 mm (1.0 inches)84%moderate

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