nomadseason

September Weather in Riverside, United States

Last updated: June 24, 2025

In Riverside, United States, the average temperature in September hovers around 18°C (64°F). Temperatures can range from a chilly 1°C (34°F) to a scorching 38°C (100°F), giving you quite the variety! Expect 20 mm (0.8 in) of precipitation spread over 3 days, with an average humidity of 46%. Perfect for those who enjoy a bit of unpredictability in their weather!

September Temperature in Riverside

In September, in Riverside, the average temperature is 18°C (64°F). Maximum temperatures can reach 38°C (100°F), while minimum temperatures can drop to as low as 1°C (34°F). Travelers should be prepared for a wide range of temperatures and pack accordingly for both warm and cool conditions.

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 18°C (64°F), with highs reaching up to 38°C (100°F) and lows dropping to around 1°C (34°F).
JanFebMarAprMayJunJulAugSepOctNovDec273041485769787464473829
Data source: Temperature data for Riverside generated using information from the Copernicus Climate Change Service.
Choose your preferred temperature unit
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 20 mm (0.8 in) accumulated over a period of 3 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 20 mm (0.8 inches) of precipitation spread over approximately 3 days.
JanFebMarAprMayJunJulAugSepOctNovDec32404037432071120292233
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
Choose your preferred precipitation unit

September Humidity in Riverside

In Riverside in September humidity is 46%. With an average temperature of 18°C (64°F), this humidity feels like a pleasant and comfortable experience for traveling, allowing for enjoyable outdoor activities without feeling overly sticky or oppressive.

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 46%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec91%92%85%76%66%62%53%42%46%64%83%87%
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.
JanFebMarAprMayJunJulAugSepOctNovDec3578101111109643
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 Weather-3°C (27°F)32 mm (1.3 inches)91%moderate
February Weather-1°C (31°F)40 mm (1.6 inches)92%moderate
March Weather5°C (41°F)40 mm (1.6 inches)85%high
April Weather9°C (48°F)37 mm (1.4 inches)76%very high
May Weather14°C (58°F)43 mm (1.7 inches)66%very high
June Weather20°C (69°F)20 mm (0.8 inches)62%extreme
July Weather25°C (78°F)7 mm (0.3 inches)53%extreme
August Weather24°C (75°F)11 mm (0.4 inches)42%very high
September Weather18°C (64°F)20 mm (0.8 inches)46%very high
October Weather8°C (48°F)29 mm (1.1 inches)64%high
November Weather3°C (38°F)22 mm (0.9 inches)83%moderate
December Weather-2°C (29°F)33 mm (1.3 inches)87%moderate

Compare Riverside's Climate with Cities Worldwide