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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 pleasant 20°C (69°F). However, temperatures can fluctuate, with minimums dipping as low as 7°C (45°F) and maximums soaring up to 41°C (105°F). You can expect a light sprinkle, with precipitation averaging just 2 mm (0.1 in) over 0 days of the month. Humidity remains quite comfortable at around 68%.

September Temperature in Santa Rosa

In September in Santa Rosa, the average temperature is 20°C (69°F). Maximum temperatures can reach 41°C (105°F), while minimums can drop as low as 7°C (45°F). Be prepared for a wide range of temperatures when traveling during this month.

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 20°C (69°F), with highs reaching up to 41°C (105°F) and lows dropping to around 7°C (45°F).
JanFebMarAprMayJunJulAugSepOctNovDec485052576269717169635348
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 2 mm (0.1 in) during a span of 0 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 2 mm (0.1 inches) of precipitation spread over approximately 0 days.
JanFebMarAprMayJunJulAugSepOctNovDec13915597452820024158101
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 68%. With an average temperature of 20°C (69°F), this humidity feels like a warm embrace, making outdoor exploration both refreshing and slightly sticky, requiring occasional breaks in the shade to stay comfortable while traveling.

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 68%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec86%84%83%80%80%76%70%66%68%72%84%84%
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 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 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 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3579101111109643
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 Weather9°C (49°F)139 mm (5.5 inches)86%moderate
February Weather10°C (50°F)155 mm (6.1 inches)84%moderate
March Weather11°C (52°F)97 mm (3.8 inches)83%high
April Weather14°C (57°F)45 mm (1.8 inches)80%very high
May Weather17°C (62°F)27 mm (1.1 inches)80%very high
June Weather21°C (69°F)2 mm (0.1 inches)76%extreme
July Weather22°C (71°F)0 mm (0.0 inches)70%extreme
August Weather21°C (71°F)0 mm (0.0 inches)66%very high
September Weather20°C (69°F)2 mm (0.1 inches)68%very high
October Weather17°C (63°F)41 mm (1.6 inches)72%high
November Weather12°C (54°F)58 mm (2.3 inches)84%moderate
December Weather9°C (48°F)101 mm (4.0 inches)84%moderate

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