Key West Weather in September

September's weather is the year's wettest for Key West, Florida. Still, the sun beams down during most of daylight.

This page gives detailed information on the typical September temperature, precipitation, sun, humidity, wind and storms for Key West. The numbers here are historical averages based on climate data gathered at the Key West International Airport, located on Key West Island.

Temperature Weather iconTemperature

89 °F September average high 30 °C
79 °F September average low 26 °C
10 days 90 °F max. or more (32 °C)
0 days 70 °F min. or less (21 °C)

Typically every September day at Key West has a temperature of at least 80 degrees Fahrenheit (27 degrees Celsius). Temperatures above 100 °F (38 °C) are not expected here this month.

Rainy Weather iconRain

7.2 in total precipitation 184 mm
16 days of rain

September is the rainiest month for Key West. Half the time, the island receives 5.6 to 8.3 inches (142 to 210 mm) of rainfall in September. One in four years has drier weather, while another one in four is wetter.

Sunny Weather iconSun

72 % sunshine
3 days clear skies

The sun's rays reach the ground in Key West during 72 percent of daylight hours on average in September, for a total of 265 hours in the month. Typically on 3 days this month the sky is mainly clear, with at most 30 percent cloud cover.

Sunlight in September at Key West lasts for 12 hours and 16 minutes a day on average. The longest day of the month is the 1st with 12 hours and 37 minutes of daylight. By the end of the month, the days have shortened to 11:56 from sunrise to sunset. These durations can vary by a minute or two from year to year.

Humid Weather iconHumidity

75 % September average humidity

The relative humidity in Key West during September usually peaks at 81 percent in the morning then drops to 69 percent by early afternoon.

Local Time1 am4 am7 am10 am1 pm4 pm7 pm10 pm
Humidity % 79 80 81 72 70 69 75 77

Windy Weather iconWind

9.5 mph September wind speed average 15.3 kph

September is less windy than most other months in Key West.

Stormy Weather iconStorms

4 days rainfall of 0.5 inches (13 mm) or more
12 days with thunderstorms in September
14 % chance a named storm approaches

There's a 6 percent probability that a hurricane will approach within 100 miles (165 km) of Key West during September. The chance of a major category 3 to 5 hurricane reaching the area is 2 percent.


The weather data here are long-term averages provided by the US National Centers for Environmental Information (NCEI). Temperature and precipitation are 1991-2020 normals while humidity and thunderstorms are 1961-1990 normals. The named storm probabilities come from the Atlantic Oceanographic and Meteorological Laboratory, Hurricane Research Division.

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