September Weather in Castaic, United States

Last updated: June 24, 2025

In Castaic, United States, the average temperature in September is a pleasant 23°C (74°F). However, temperatures can vary greatly, with a minimum of 9°C (48°F) and a possible maximum of 43°C (110°F). With only 4 mm (0.2 in) of precipitation expected across 1 day, you can generally expect a fairly dry climate, complemented by an average humidity of 48%.

September Temperature in Castaic

In September in Castaic, the average temperature is 23°C (74°F). Maximum temperatures can reach 43°C (110°F), while minimums can dip as low as 9°C (48°F). Be prepared for a wide range of weather conditions if you're planning to travel during this time!

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

The chart illustrates September temperature patterns in Castaic, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Castaic, September typically has an average temperature of 23°C (74°F), with highs reaching up to 43°C (110°F) and lows dropping to around 9°C (48°F).

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

September Precipitation in Castaic

In Castaic in September, the precipitation amount is 4 mm (0.2 in) during 1 day.

September Precipitation Trends in Castaic

The chart displays monthly precipitation patterns in Castaic, 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 Castaic, September typically receives around 4 mm (0.2 inches) of precipitation spread over approximately 1 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 Castaic

In Castaic in September humidity is 48%. With an average temperature of 23°C (74°F), this humidity feels like a refreshing but slightly muggy embrace, making traveling enjoyable with a light breeze, yet prompting travelers to stay hydrated and take occasional breaks from the sun.

September Average Humidity in Castaic

This chart illustrates the average monthly humidity levels in Castaic, 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 Castaic is approximately 48%, 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 Castaic

In Castaic in September, the maximum UV index reaches 10, which corresponds to a very high Exposure Category. With a time to burn of just 15 minutes, it's crucial to take precautions. For more detailed information, you can check the Hourly UV Index in Castaic.

Maximum UV Index Levels in Castaic for September

The chart shows the monthly maximum UV Index (UVI) for Castaic 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 Castaic typically reaches 10, which falls under the very high exposure category.

Data source: Castaic 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 Castaic Compares to Other Months

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

This table compares monthly weather conditions in Castaic, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
	Temperature	Precipitation	Humidity	UV
January Weather	10°C (51°F)	63 mm (2.5 inches)	78%	moderate
February Weather	11°C (52°F)	55 mm (2.2 inches)	82%	high
March Weather	12°C (55°F)	71 mm (2.8 inches)	75%	very high
April Weather	16°C (62°F)	22 mm (0.9 inches)	68%	very high
May Weather	18°C (65°F)	16 mm (0.6 inches)	57%	extreme
June Weather	22°C (72°F)	3 mm (0.1 inches)	52%	extreme
July Weather	25°C (78°F)	1 mm (0.1 inches)	46%	extreme
August Weather	26°C (78°F)	2 mm (0.1 inches)	39%	extreme
September Weather	23°C (74°F)	4 mm (0.2 inches)	48%	very high
October Weather	19°C (66°F)	9 mm (0.3 inches)	59%	high
November Weather	15°C (59°F)	19 mm (0.7 inches)	72%	moderate
December Weather	10°C (51°F)	68 mm (2.7 inches)	76%	moderate