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September Weather in Keys, United States

Last updated: June 24, 2025

In September, the average temperature in Keys, United States is a comfortable 24°C (76°F), perfect for outdoor activities. However, be prepared for a range of temperatures that can drop as low as 8°C (48°F) and soar up to 38°C (100°F). Expect about 78 mm (3.1 in) of precipitation spread over 5 days, contributing to an average humidity of 64%.

September Temperature in Keys

In September in Keys, the average temperature is a pleasant 24°C (76°F). The maximum can reach a scorching 38°C (100°F), while the minimum can drop to a chilly 8°C (48°F). Travelers should be prepared for a wide range of temperatures during this time.

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

The chart illustrates September temperature patterns in Keys, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Keys, September typically has an average temperature of 24°C (76°F), with highs reaching up to 38°C (100°F) and lows dropping to around 8°C (48°F).
JanFebMarAprMayJunJulAugSepOctNovDec394254596978827976625045
Data source: Temperature data for Keys 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 Keys

In Keys in September, the total precipitation amount is 78 mm (3.1 in) spread over a duration of 5 days.

September Precipitation Trends in Keys

The chart displays monthly precipitation patterns in Keys, 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 Keys, September typically receives around 78 mm (3.1 inches) of precipitation spread over approximately 5 days.
JanFebMarAprMayJunJulAugSepOctNovDec8910013415821278105129781536683
Data source: Precipitation data for September generated using information from the Copernicus Climate Change Service.
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September Humidity in Keys

In Keys in September, humidity is 64%. With an average temperature of 24°C (76°F), this humidity feels like a warm, sticky embrace, making travel slightly uncomfortable but still enjoyable, as you may find yourself yearning for a refreshing breeze or a quick dip in the water.

September Average Humidity in Keys

This chart illustrates the average monthly humidity levels in Keys, 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 Keys is approximately 64%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec79%78%75%75%83%82%78%68%64%71%82%87%
Data source: Humidity data for September generated using information from the Copernicus Climate Change Service.

September UV Index in Keys

In Keys 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 Keys.

Maximum UV Index Levels in Keys for September

The chart shows the monthly maximum UV Index (UVI) for Keys 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 Keys typically reaches 9, which falls under the very high exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec46710101111109753
Data source: Keys 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 Keys Compares to Other Months

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

This table compares monthly weather conditions in Keys, showing how September’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather4°C (40°F)89 mm (3.5 inches)79%moderate
February Weather6°C (42°F)100 mm (4.0 inches)78%high
March Weather12°C (54°F)134 mm (5.3 inches)75%high
April Weather15°C (59°F)158 mm (6.2 inches)75%very high
May Weather21°C (69°F)212 mm (8.3 inches)83%very high
June Weather26°C (78°F)78 mm (3.1 inches)81%extreme
July Weather28°C (82°F)105 mm (4.1 inches)78%extreme
August Weather26°C (80°F)129 mm (5.1 inches)68%very high
September Weather24°C (76°F)78 mm (3.1 inches)64%very high
October Weather17°C (62°F)153 mm (6.0 inches)71%high
November Weather10°C (50°F)66 mm (2.6 inches)82%moderate
December Weather7°C (45°F)83 mm (3.3 inches)87%moderate

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