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September Weather in California, United States

Last updated: June 24, 2025

In California, United States, the average temperature in September is a pleasant 22°C (73°F). However, be prepared for a range, as temperatures can drop to a minimum of 7°C (44°F) and soar up to a maximum of 35°C (96°F). During this time, expect approximately 61 mm (2.4 in) of precipitation spread over 6 days, with an average humidity of 72% adding a touch of summer warmth to the air.

September Temperature in California

In September, in California, the average temperature is 22°C (73°F). Maximum temperatures can reach 35°C (96°F), while minimums can drop to as low as 7°C (44°F). This makes California an ideal destination for travelers seeking warm weather during the day, with cooler evenings perfect for comfortable outdoor activities.

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 22°C (73°F), with highs reaching up to 35°C (96°F) and lows dropping to around 7°C (44°F).
JanFebMarAprMayJunJulAugSepOctNovDec323547546676807672584539
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 61 mm (2.4 in) spread over a period of 6 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 61 mm (2.4 inches) of precipitation spread over approximately 6 days.
JanFebMarAprMayJunJulAugSepOctNovDec6860114124176113115106611075638
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 72%. With an average temperature of 22°C (73°F), this humidity feels like a warm embrace, making it ideal for leisurely strolls but potentially uncomfortable for prolonged outdoor activities.

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 72%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec80%78%75%77%82%83%81%78%72%72%84%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 9, which corresponds to a very high Exposure Category. The time to burn is just 15 minutes, so it's essential to take precautions. For detailed information, you can check 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 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3579101111109743
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)68 mm (2.7 inches)80%moderate
February Weather1°C (35°F)60 mm (2.4 inches)78%moderate
March Weather8°C (47°F)114 mm (4.5 inches)75%high
April Weather12°C (55°F)124 mm (4.9 inches)77%very high
May Weather19°C (67°F)175 mm (6.9 inches)82%very high
June Weather25°C (77°F)113 mm (4.4 inches)83%extreme
July Weather26°C (80°F)115 mm (4.5 inches)81%extreme
August Weather25°C (77°F)106 mm (4.2 inches)78%very high
September Weather22°C (73°F)61 mm (2.4 inches)72%very high
October Weather14°C (58°F)107 mm (4.2 inches)72%high
November Weather7°C (45°F)56 mm (2.2 inches)84%moderate
December Weather4°C (39°F)38 mm (1.5 inches)86%moderate

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