September Weather in California, Mexico

Last updated: August 27, 2025

In September, the average temperature in California, Mexico is a comfortable 19°C (66°F). You can expect temperatures to range from a minimum of 9°C (49°F) to a maximum of 29°C (84°F). Be prepared for some rain, as 135 mm (5.3 in) of precipitation can fall over about 15 days. With an average humidity of 81%, the air can feel quite moist—perfect for a lush, vibrant atmosphere!

September Temperature in California

In September in California, the average temperature is 19°C (66°F). The maximum can reach 29°C (84°F) and the minimum can be as low as 9°C (49°F). This pleasant climate makes California an ideal destination for travelers seeking enjoyable weather during their visit.

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 19°C (66°F), with highs reaching up to 29°C (84°F) and lows dropping to around 9°C (49°F).

Data source: Temperature data for California generated using information from the Copernicus Climate Change Service.

September Precipitation in California

In California in September, the precipitation amount is 135 mm (5.3 in), occurring over a span of 15 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 135 mm (5.3 inches) of precipitation spread over approximately 15 days.

Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.

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Millimeters (mm) Inches (in)

September Humidity in California

In California in September, humidity is 81%. With an average temperature of 19°C (66°F), this humidity feels like a warm, heavy blanket enveloping you, making travel feel both muggy and slightly stifling, often leading to a need for frequent breaks in the shade.

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 81%, offering insight into how humid the weather typically is during this month.

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 14, which corresponds to an extreme Exposure Category. The time to burn is just 10 minutes, so it's crucial to take precautions. For the detailed hourly UV index in California, you can check here.

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 14, which falls under the extreme exposure category.

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.
	Temperature	Precipitation	Humidity	UV
January Weather	13°C (55°F)	18 mm (0.7 inches)	75%	very high
February Weather	15°C (59°F)	11 mm (0.4 inches)	69%	extreme
March Weather	18°C (65°F)	10 mm (0.4 inches)	65%	extreme
April Weather	20°C (68°F)	6 mm (0.2 inches)	64%	extreme
May Weather	22°C (71°F)	30 mm (1.2 inches)	75%	extreme
June Weather	21°C (70°F)	116 mm (4.6 inches)	78%	extreme
July Weather	20°C (68°F)	137 mm (5.4 inches)	67%	extreme
August Weather	20°C (68°F)	79 mm (3.1 inches)	64%	extreme
September Weather	19°C (66°F)	135 mm (5.3 inches)	81%	extreme
October Weather	18°C (64°F)	48 mm (1.9 inches)	85%	extreme
November Weather	15°C (60°F)	14 mm (0.6 inches)	87%	very high
December Weather	13°C (55°F)	12 mm (0.5 inches)	87%	very high