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September Weather in Riverside, United States

Last updated: June 24, 2025

In September, the average temperature in Riverside, United States is a pleasant 25°C (76°F). Expect a range that can drop to a cool 11°C (52°F) at its lowest and soar up to a warm 36°C (97°F) at its highest. With about 87 mm (3.4 in) of precipitation spread over 10 days, the average humidity sits at a comfortable 73%, making for a vibrant yet refreshing atmosphere.

September Temperature in Riverside

In September in Riverside, the average temperature is 25°C (76°F). Maximums can reach 36°C (97°F), while minimums can drop as low as 11°C (52°F). This makes it a great time for travelers who enjoy warm weather while still having the option for cooler evenings.

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

The chart illustrates September temperature patterns in Riverside, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Riverside, September typically has an average temperature of 25°C (76°F), with highs reaching up to 36°C (97°F) and lows dropping to around 11°C (52°F).
JanFebMarAprMayJunJulAugSepOctNovDec465258637277807976675349
Data source: Temperature data for Riverside 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 Riverside

In Riverside in September, the precipitation amount is 87 mm (3.4 in) over the course of 10 days.

September Precipitation Trends in Riverside

The chart displays monthly precipitation patterns in Riverside, 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 Riverside, September typically receives around 87 mm (3.4 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec1191611341431041421101308712086144
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Riverside

In Riverside in September, humidity is 73%. With an average temperature of 25°C (76°F), this humidity feels like walking through a warm, wet blanket, making travel feel sluggish and sticky, as the air clings to your skin and saps your energy while exploring.

September Average Humidity in Riverside

This chart illustrates the average monthly humidity levels in Riverside, 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 Riverside is approximately 73%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%84%82%82%81%77%77%72%73%73%85%88%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Riverside

In Riverside 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 Riverside.

Maximum UV Index Levels in Riverside for September

The chart shows the monthly maximum UV Index (UVI) for Riverside 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 Riverside typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec47810111111109764
Data source: Riverside 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 Riverside Compares to Other Months

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

This table compares monthly weather conditions in Riverside, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather8°C (47°F)119 mm (4.7 inches)85%moderate
February Weather11°C (52°F)161 mm (6.3 inches)84%high
March Weather14°C (58°F)134 mm (5.3 inches)82%very high
April Weather17°C (63°F)143 mm (5.6 inches)82%very high
May Weather22°C (72°F)104 mm (4.1 inches)81%extreme
June Weather25°C (77°F)142 mm (5.6 inches)77%extreme
July Weather27°C (80°F)110 mm (4.3 inches)77%extreme
August Weather26°C (80°F)130 mm (5.1 inches)72%very high
September Weather25°C (76°F)87 mm (3.4 inches)73%very high
October Weather19°C (67°F)120 mm (4.7 inches)73%high
November Weather12°C (53°F)86 mm (3.4 inches)85%high
December Weather10°C (50°F)144 mm (5.7 inches)88%moderate

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