September weather forecast
Key West, FL

A beach pier in Key West, Florida, with palm trees in the background
A beach pier in Key West, Florida, with palm trees in the background

Weather in September

The first month of the autumn, September, is still a warm month in Key West, Florida, with temperature in the range of an average low of 82.2°F (27.9°C) and an average high of 84.4°F (29.1°C).

Temperature

In September, the average high-temperature is essentially the same as in August - a still warm 84.4°F (29.1°C). In September, the average low-temperature is 82.2°F (27.9°C).

Heat index

The average heat index in September is appraised at a tropical 92.7°F (33.7°C). Take extra precautions, as heat cramps and heat exhaustion are possible. Sustained activity may result in heatstroke.
Take into consideration that the heat index values are calculated for shade and light wind conditions. Exposure to direct sunshine can increase heat index values by up to 15 Fahrenheit (8 Celsius) degrees.
Note: The heat index, also known as 'real feel', 'feels like', 'felt air temperature', or 'apparent temperature', is calculated by taking the relative humidity value for a specific location and factoring it into the air temperature reading. Additional factors like clothing, wind, pregnancy, and activity influence one's weather impression. Bear in mind that direct sunshine exposure increases weather impact, and may raise heat index by up to 15 Fahrenheit (8 Celsius) degrees. Heat index values are particularly important for children. Young children are generally more endangered than adults, as they usually less sweat. And also, due to larger skin surface relative to their small bodies and higher heat production as a result of their activity.

Humidity

The months with the lowest humidity are July through September, with an average relative humidity of 74%.

Rainfall

September is the month with the most rainfall. Rain falls for 23.1 days and accumulates 5.12" (130mm) of precipitation.

Ocean temperature

In Key West, the average seawater temperature in September is 85.6°F (29.8°C).
Note: For swimming, diving, and other water activities, temperatures between 77°F (25°C) and 84.2°F (29°C) are perceived as very enjoyable and pleasurable for prolonged periods without feeling uncomfortable.

Daylight

In September, the average length of the day is 12h and 17min.
On the first day of the month, sunrise is at 7:08 am and sunset at 7:45 pm. On the last day of September, in Key West, sunrise is at 7:18 am and sunset at 7:15 pm EDT.

Sunshine

In Key West, the average sunshine in September is 9h.

UV index

The months with the highest UV index are April through October, with an average maximum UV index of 7. A UV Index estimate of 6 to 7 represents a high threat to health from unsafe exposure to UV radiation for the ordinary person.
Note: The average daily UV index of 7 in September transform into the following instructions:
Take precautions and adopt sun safety practices. Protection against sunburn is obliged. The Sun's UV radiation is most powerful between 10 a.m. and 4 p.m. To the extent possible, limit exposure to the direct sun during these hours. A wide-brim hat offers excellent sun protection for the eyes, ears, face, and neck. Sunglasses with UVA and UVB protection significantly reduce eye damage from sun exposure. Tightly woven, loose-fitting clothes provide additional protection from the Sun. Beware! The strength of the UV rays is significantly increased by the reflection of the water and sand.
[Resources]

FAQ

What is the temperature in September in Key West?

In Key West, Florida, in September, the average high-temperature is 84.4°F (29.1°C), and the average low-temperature is 82.2°F (27.9°C). The average heat index (a.k.a. 'feels like', 'real feel'), which calculates the temperature value influenced by the moisture in the air, in September is appraised at 92.7°F (33.7°C).

What are the least humid months in Key West?

July through September, with an average relative humidity of 74%, are the least humid months in Key West.

What is the average humidity in September in Key West?

The average relative humidity in September in Key West is 74%.

What is the wettest month in Key West?

The month with the most rainfall is September, when the rain falls for 23.1 days and typically aggregates up to 5.12" (130mm) of precipitation.

How many days does it rain in September in Key West?

In September, in Key West, Florida, the rain falls for 23.1 days. Throughout September, 5.12" (130mm) of precipitation is accumulated.

What is the water temperature in September in Key West?

In Key West, Florida, in September, the average water temperature is 85.6°F (29.8°C). For swimming, diving, and other water activities, temperatures between 77°F (25°C) and 84.2°F (29°C) are perceived as very enjoyable and pleasurable for prolonged periods without feeling uncomfortable.

What is the average length of the day in September in Key West?

In Key West, the average day length in September is 12h and 17min.

When are sunrise and sunset in September in Key West?

On the first day of September in Key West, sunrise is at 7:08 am and sunset at 7:45 pm. On the last day of the month, sunrise is at 7:18 am and sunset at 7:15 pm EDT.

How many hours of sunshine does Key West have in September?

The average sunshine duration in September in Key West, Florida, is 9h.

What are the months with the highest UV index in Key West?

April through October, with an average maximum UV index of 7, are months with the highest UV index in Key West, Florida.

What is the UV index reading in September in Key West?

The average daily maximum UV index in September in Key West is 7. A UV Index value of 6 to 7 symbolizes a high health vulnerability from unsafe exposure to Sun's UV rays.

Average temperature in September
Key West, FL

Average temperature in September - Key West, FL
  • Average high temperature in September: 84.4°F

The warmest month (with the highest average high temperature) is August (85.3°F).
The month with the lowest average high temperature is January (72.7°F).

  • Average low temperature in September: 82.2°F

The month with the highest average low temperature is August (82.9°F).
The coldest month (with the lowest average low temperature) is January (68.5°F).

[Resources]

Average pressure in September
Key West, FL

Average pressure in September - Key West, FL
  • Average pressure in September: 29.93"Hg

The month with the highest atmospheric pressure is January (30.09"Hg).
The months with the lowest atmospheric pressure are September and October (29.93"Hg).

[Resources]

Average wind speed in September
Key West, FL

Average wind speed in September - Key West, FL
  • Average wind speed in September: 10.3mph

The windiest months (with the highest average wind speed) are January and November (14.4mph).
The calmest month (with the lowest average wind speed) is July (9.5mph).

[Resources]

Average humidity in September
Key West, FL

Average humidity in September - Key West, FL
  • Average humidity in September: 74%

The month with the highest relative humidity is February (78%).
The months with the lowest relative humidity are July, August and September (74%).

[Resources]

Average rainfall in September
Key West, FL

Average rainfall in September - Key West, FL
  • Average rainfall in September: 5.12"

The wettest month (with the highest rainfall) is September (5.12").
The driest month (with the least rainfall) is March (0.67").

[Resources]

Average rainfall days in September
Key West, FL

Average rainfall days in September - Key West, FL
  • Average rainfall days in September: 23.1 days

The months with the highest number of rainy days are August and September (23.1 days).
The month with the least rainy days is February (11 days).

[Resources]

Average sea temperature in September
Key West, FL

Average sea temperature in September - Key West, FL
  • Average sea temperature in September: 85.6°F

The best month for swimming (with the highest average sea temperature) is August (86.9°F).
The coldest months (with the lowest average sea temperature) are January and February (71.2°F).

[Resources]

Average daylight in September /
Average sunshine in September
Key West, FL

Average daylight in September / Average sunshine in September - Key West, FL
  • Average daylight in September: 12h and 17min

The month with the longest days is June (Average daylight: 13h and 38min).
The month with the shortest days is December (Average daylight: 10h and 39min).

  • Average sunshine in September: 9h and 0min

The month with the most sunshine is July (Average sunshine: 11h and 0min).
The month with the least sunshine is December (Average sunshine: 6h and 18min).

[Resources]

Average sunshine days in September
Key West, FL

Average sunshine days in September - Key West, FL
  • Average sunshine days in September: 4.5 days

The month with the most sunshine days is March (17 days).
The month with the least sunshine days is September (4.5 days).

[Resources]

Average UV index in September
Key West, FL

Average UV index in September - Key West, FL
  • Average UV index in September: 7

The months with the highest UV index are April, May, June, July, August, September and October (UV index 7).
The month with the lowest UV index is January (UV index 5).

[Resources]

Average cloud cover in September
Key West, FL

Average cloud cover in September - Key West, FL
  • Average cloud cover in September: 29

The month with the most cloud cover is January (Cloud cover 34).
The month with the least cloud cover is April (Cloud cover 23).

[Resources]

Average visibility in September
Key West, FL

Average visibility in September - Key West, FL
  • Average visibility in September: 6mi

The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).

[Resources]

Weather forecast for your location

1. Click Locate me button
2. Allow the app to use your location
* you will be automatically redirected to the weather forecast for your location