September Weather in Petaluma, United States

Last updated: June 24, 2025

The average temperature in Petaluma, United States during September is a pleasant 18°C (65°F). Expect a minimum of 8°C (48°F) and a maximum of 36°C (96°F), offering a nice range for various activities. Rainfall is minimal, with only 2 mm (0.1 in) expected over 0 days, and the average humidity sits comfortably at 68%. Enjoy the mild climate!

September Temperature in Petaluma

In September in Petaluma, the average temperature is 18°C (65°F). Maximums can reach up to 36°C (96°F), while minimums can drop as low as 8°C (48°F). This variability makes it advisable for travelers to pack both light clothing for the warmer days and warmer layers for cooler evenings.

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

The chart illustrates September temperature patterns in Petaluma, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Petaluma, September typically has an average temperature of 18°C (65°F), with highs reaching up to 36°C (96°F) and lows dropping to around 8°C (48°F).

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

September Precipitation in Petaluma

In Petaluma in September, the precipitation amount is 2 mm (0.1 in) during a span of 0 days.

September Precipitation Trends in Petaluma

The chart displays monthly precipitation patterns in Petaluma, 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 Petaluma, September typically receives around 2 mm (0.1 inches) of precipitation spread over approximately 0 days.

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

Choose your preferred precipitation unit

Millimeters (mm) Inches (in)

September Humidity in Petaluma

In Petaluma in September, humidity is 68%. With an average temperature of 18°C (65°F), this humidity feels like a warm, enveloping blanket, making travel somewhat sticky and requiring occasional breaks for refreshing hydration.

September Average Humidity in Petaluma

This chart illustrates the average monthly humidity levels in Petaluma, 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 Petaluma is approximately 68%, 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 Petaluma

In Petaluma 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 Petaluma.

Maximum UV Index Levels in Petaluma for September

The chart shows the monthly maximum UV Index (UVI) for Petaluma 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 Petaluma typically reaches 9, which falls under the very high exposure category.

Data source: Petaluma 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 Petaluma Compares to Other Months

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

This table compares monthly weather conditions in Petaluma, 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 (50°F)	131 mm (5.2 inches)	86%	moderate
February Weather	10°C (51°F)	147 mm (5.8 inches)	84%	moderate
March Weather	11°C (52°F)	93 mm (3.7 inches)	83%	high
April Weather	13°C (56°F)	45 mm (1.8 inches)	80%	very high
May Weather	15°C (60°F)	27 mm (1.0 inches)	80%	very high
June Weather	18°C (65°F)	2 mm (0.1 inches)	76%	extreme
July Weather	18°C (65°F)	1 mm (0.0 inches)	70%	extreme
August Weather	18°C (65°F)	1 mm (0.0 inches)	66%	very high
September Weather	18°C (65°F)	2 mm (0.1 inches)	68%	very high
October Weather	16°C (61°F)	38 mm (1.5 inches)	72%	high
November Weather	12°C (54°F)	59 mm (2.3 inches)	84%	moderate
December Weather	9°C (49°F)	103 mm (4.1 inches)	84%	moderate