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September Weather in Rio, United States

Last updated: August 27, 2025

In September, the average temperature in Rio, United States hovers around 18°C (65°F), with fluctuations that can range from a cool 2°C (35°F) to a warm 33°C (92°F). Expect about 98 mm (3.8 in) of precipitation over 10 days and a comfortable average humidity of 79%.

September Temperature in Rio

In September in Rio, the average temperature is 18°C (65°F). The maximum can reach 33°C (92°F), while the minimum can drop as low as 2°C (35°F). This diverse climate makes Rio a great destination for travelers seeking both warmth and cool, refreshing conditions.

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

The chart illustrates September temperature patterns in Rio, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Rio, September typically has an average temperature of 18°C (65°F), with highs reaching up to 33°C (92°F) and lows dropping to around 2°C (35°F).
JanFebMarAprMayJunJulAugSepOctNovDec212135455970747164513628
Data source: Temperature data for Rio 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 Rio

In Rio in September, the precipitation amount is 98 mm (3.8 in) spread over a period of 10 days.

September Precipitation Trends in Rio

The chart displays monthly precipitation patterns in Rio, 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 Rio, September typically receives around 98 mm (3.8 inches) of precipitation spread over approximately 10 days.
JanFebMarAprMayJunJulAugSepOctNovDec47525898127112103100981134446
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Rio

In Rio in September, humidity is 79%. With an average temperature of 18°C (65°F), this humidity feels like walking through a warm mist, making traveling slightly uncomfortable and sticky, but offering a refreshing escape when you find moments of shade or a breeze.

September Average Humidity in Rio

This chart illustrates the average monthly humidity levels in Rio, 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 Rio is approximately 79%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec85%85%85%85%78%80%78%76%79%83%88%82%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Rio

In Rio in September, the maximum UV index is 7, which corresponds to the high Exposure Category. This means that the time to burn is approximately 25 minutes. For more detailed information, you can check the Hourly UV Index in Rio.

Maximum UV Index Levels in Rio for September

The chart shows the monthly maximum UV Index (UVI) for Rio 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 Rio typically reaches 7, which falls under the high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec34589101097532
Data source: Rio 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 Rio Compares to Other Months

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

This table compares monthly weather conditions in Rio, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-6°C (21°F)47 mm (1.9 inches)85%moderate
February Weather-6°C (21°F)52 mm (2.0 inches)85%moderate
March Weather2°C (35°F)58 mm (2.3 inches)85%moderate
April Weather7°C (45°F)98 mm (3.9 inches)85%very high
May Weather15°C (59°F)127 mm (5.0 inches)78%very high
June Weather21°C (70°F)112 mm (4.4 inches)80%very high
July Weather23°C (74°F)103 mm (4.1 inches)78%very high
August Weather22°C (71°F)100 mm (3.9 inches)76%very high
September Weather18°C (65°F)98 mm (3.8 inches)79%high
October Weather10°C (51°F)113 mm (4.5 inches)83%moderate
November Weather2°C (36°F)44 mm (1.7 inches)88%moderate
December Weather-2°C (28°F)46 mm (1.8 inches)81%low

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