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September Weather in Santa Rosa, United States

Last updated: June 24, 2025

The average temperature in Santa Rosa, United States during September is a warm 28°C (83°F), making it a perfect time for outdoor activities. However, temperatures can vary, with minimums dropping to 18°C (64°F) and maximums rising to 38°C (101°F). Expect about 114 mm (4.5 in) of precipitation spread over 15 days, while the average humidity lingers at a comfortable 73%.

September Temperature in Santa Rosa

In September in Santa Rosa, the average temperature is 28°C (83°F), with maximums soaring to 38°C (101°F) and minimums dipping to 18°C (64°F). This climate makes it an ideal time for travelers seeking warm weather and outdoor adventures.

September Weather in Santa Rosa: Daily Temperature Highs, Lows, and Averages

The chart illustrates September temperature patterns in Santa Rosa, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Santa Rosa, September typically has an average temperature of 28°C (83°F), with highs reaching up to 38°C (101°F) and lows dropping to around 18°C (64°F).
JanFebMarAprMayJunJulAugSepOctNovDec626572768284868783776964
Data source: Temperature data for Santa Rosa 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 Santa Rosa

In Santa Rosa in September, the precipitation amount is 114 mm (4.5 in) spread over a duration of 15 days.

September Precipitation Trends in Santa Rosa

The chart displays monthly precipitation patterns in Santa Rosa, 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 Santa Rosa, September typically receives around 114 mm (4.5 inches) of precipitation spread over approximately 15 days.
JanFebMarAprMayJunJulAugSepOctNovDec2421353081919433114653023
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Santa Rosa

In Santa Rosa in September, humidity is 73%. With an average temperature of 28°C (83°F), this humidity feels like a thick blanket enveloping your skin, making travel feel heavy and stifling, often requiring frequent breaks in shaded or air-conditioned areas to stay comfortable.

September Average Humidity in Santa Rosa

This chart illustrates the average monthly humidity levels in Santa Rosa, 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 Santa Rosa is approximately 73%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec83%79%76%77%80%73%66%65%73%76%80%86%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Santa Rosa

In Santa Rosa in September, the maximum UV index reaches 11, which corresponds to an extreme Exposure Category. With a time to burn of just 10 minutes, it's essential to take precautions. For more details, you can check the Hourly UV Index in Santa Rosa.

Maximum UV Index Levels in Santa Rosa for September

The chart shows the monthly maximum UV Index (UVI) for Santa Rosa 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 Santa Rosa typically reaches 11, which falls under the extreme exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec69101112121212111076
Data source: Santa Rosa 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 Santa Rosa Compares to Other Months

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

This table compares monthly weather conditions in Santa Rosa, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather17°C (62°F)24 mm (1.0 inches)83%high
February Weather18°C (65°F)21 mm (0.8 inches)79%very high
March Weather22°C (72°F)35 mm (1.4 inches)76%very high
April Weather25°C (77°F)30 mm (1.2 inches)77%extreme
May Weather28°C (82°F)81 mm (3.2 inches)80%extreme
June Weather29°C (85°F)91 mm (3.6 inches)73%extreme
July Weather30°C (86°F)94 mm (3.7 inches)66%extreme
August Weather30°C (87°F)33 mm (1.3 inches)65%extreme
September Weather28°C (83°F)114 mm (4.5 inches)73%extreme
October Weather25°C (77°F)64 mm (2.5 inches)76%very high
November Weather21°C (69°F)30 mm (1.2 inches)80%high
December Weather18°C (65°F)23 mm (0.9 inches)86%high

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