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September Weather in California, United States

Last updated: June 24, 2025

In September, the average temperature in California, United States hovers around 20°C (68°F). Expect a minimum of 5°C (40°F) and a maximum of 33°C (92°F). During this month, precipitation is around 125 mm (4.9 in) spread over 9 days, and humidity averages at a comfortable 73%.

September Temperature in California

In September in California, the average temperature is 20°C (68°F). Maximums can reach 33°C (92°F) and minimums can be as low as 5°C (40°F). Be prepared for a range of temperatures, making it ideal for both outdoor activities and cozy evenings.

September Weather in California: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in California, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In California, September typically has an average temperature of 20°C (68°F), with highs reaching up to 33°C (92°F) and lows dropping to around 5°C (40°F).
JanFebMarAprMayJunJulAugSepOctNovDec323643536370757368584337
Data source: Temperature data for California 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 California

In California in September, the total precipitation amount is 125 mm (4.9 in) recorded over a span of 9 days.

September Precipitation Trends in California

The chart displays monthly precipitation patterns in California, 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 California, September typically receives around 125 mm (4.9 inches) of precipitation spread over approximately 9 days.
JanFebMarAprMayJunJulAugSepOctNovDec8712411712914917215311012512186116
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in California

In California in September, humidity is 73%. With an average temperature of 20°C (68°F), this humidity feels like a warm embrace, making outdoor activities somewhat sticky, yet the atmosphere remains pleasant for leisurely strolls and sightseeing.

September Average Humidity in California

This chart illustrates the average monthly humidity levels in California, 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 California is approximately 73%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec88%88%88%87%82%84%82%73%74%81%89%86%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in California

In California 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 California.

Maximum UV Index Levels in California for September

The chart shows the monthly maximum UV Index (UVI) for California 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 California typically reaches 8, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec357910101098643
Data source: California 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 California Compares to Other Months

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

This table compares monthly weather conditions in California, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather0°C (33°F)87 mm (3.4 inches)88%moderate
February Weather2°C (37°F)124 mm (4.9 inches)88%moderate
March Weather6°C (43°F)117 mm (4.6 inches)88%high
April Weather11°C (53°F)129 mm (5.1 inches)86%very high
May Weather17°C (63°F)149 mm (5.9 inches)82%very high
June Weather21°C (70°F)172 mm (6.8 inches)84%very high
July Weather24°C (75°F)153 mm (6.0 inches)82%very high
August Weather23°C (73°F)110 mm (4.3 inches)73%very high
September Weather20°C (68°F)125 mm (4.9 inches)73%very high
October Weather14°C (58°F)121 mm (4.8 inches)81%high
November Weather6°C (43°F)86 mm (3.4 inches)89%moderate
December Weather3°C (38°F)116 mm (4.6 inches)86%moderate

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