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September Weather in San Jose, United States

Last updated: June 24, 2025

In San Jose, United States during September, the average temperature is a comfortable 21°C (71°F). You can expect minimum temperatures to drop to 6°C (42°F), while highs can reach a sizzling 35°C (96°F). Be prepared for 65 mm (2.6 in) of precipitation over the course of 7 days, and anticipate a high average humidity of around 80%. Enjoy your stay!

September Temperature in San Jose

In September in San Jose, the average temperature is 21°C (71°F). Maximums can reach 35°C (96°F), while minimums can drop to as low as 6°C (42°F). It's advisable to pack both light clothing for the warmer days and a jacket for the cooler evenings.

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 21°C (71°F), with highs reaching up to 35°C (96°F) and lows dropping to around 6°C (42°F).
JanFebMarAprMayJunJulAugSepOctNovDec283143526574777470574135
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 total precipitation amount is 65 mm (2.6 in) over a span of 7 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 65 mm (2.6 inches) of precipitation spread over approximately 7 days.
JanFebMarAprMayJunJulAugSepOctNovDec676912112115213111597651156453
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 80%. With an average temperature of 21°C (71°F), this humidity feels like a warm, heavy blanket wrapping around you, making outdoor activities feel more exhausting and requiring frequent breaks to stay hydrated.

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 80%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec82%83%84%85%79%82%80%81%80%82%88%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 is 8, which corresponds to a very high Exposure Category. This means that the time to burn is only 15 minutes. For more detailed information, you can refer to 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 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec357810111098642
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 Weather-2°C (28°F)67 mm (2.6 inches)82%moderate
February Weather-1°C (31°F)69 mm (2.7 inches)83%moderate
March Weather6°C (43°F)121 mm (4.8 inches)84%high
April Weather11°C (52°F)121 mm (4.8 inches)85%very high
May Weather18°C (65°F)152 mm (6.0 inches)79%very high
June Weather24°C (75°F)131 mm (5.2 inches)82%extreme
July Weather25°C (77°F)115 mm (4.5 inches)80%very high
August Weather23°C (74°F)97 mm (3.8 inches)81%very high
September Weather21°C (71°F)65 mm (2.6 inches)80%very high
October Weather14°C (57°F)115 mm (4.5 inches)82%high
November Weather5°C (41°F)64 mm (2.5 inches)88%moderate
December Weather2°C (36°F)53 mm (2.1 inches)84%low

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