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Average Weather in Key West Florida, United States

In Key West, the temperature typically varies from 65°F to 89°F over the course of the year, and is rarely below 56°F or above 91°F.

The hot season lasts for 123 days, from June 1 to October 2, with an average daily high temperature above 86°F. The hottest day of the year is August 7, with an average high of 89°F and low of 81°F.

The cool season lasts for 89 days, from December 7 to March 6, with an average daily high temperature below 77°F. The coldest day of the year is January 18, with an average low of 65°F and high of 74°F.

Average High and Low Temperature

The daily average high (red line) and low (blue line) temperature with percentile bands, with 25th to 75th and 10th to 90th percentile bands. The thin dotted lines are the corresponding average perceived temperatures.

The figure below shows you a compact characterization of the entire year of hourly average temperatures. The horizontal axis is the day of the year, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Average Hourly Temperature

12 AM4 AM8 AM12 PM4 PM8 PM12 AMJanFebMarAprMayJunJulAugSepOctNovDeccomfortablecomfortablewarmwarmhothot
The average hourly temperature, color coded into bands: frigid < 15°F < freezing < 32°F < chilly < 45°F < cold < 55°F < cool < 65°F < comfortable < 75°F < warm < 85°F < hot < 95°F < sweltering. The shaded overlays indicate night and civil twilight.

Sun

The length of the day in Key West varies over the course of the year. In 2017, the shortest day is December 21, with 10 hours, 37 minutes of daylight; the longest day is June 21, with 13 hours, 40 minutes of daylight.

Hours of Daylight and Twilight

The number of hours during which the Sun is visible (black line). From bottom (most yellow) to top (most gray), the color bands indicate: full daylight, twilight (civil, nautical, and astronomical), and full night.

The earliest sunrise is at 6:36 AM on November 5, and the latest sunrise is 1 hour, 2 minutes later at 7:38 AM on March 12. The earliest sunset is at 5:37 PM on November 29, and the latest sunset is 2 hours, 42 minutes later at 8:20 PM on July 2.

Daylight saving time (DST) is observed in Key West during 2017, starting in the spring on March 12, lasting 237 days, and ending in the fall on November 5.

Sunrise & Sunset with Twilight and Daylight Saving Time

The solar day over the course of the year 2017. From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight saving time are indicated by the 'DST' labels.

Clouds

In Key West, the average percentage of the sky covered by clouds experiences significant seasonal variation over the course of the year.

The clearer part of the year in Key West begins around October 19 and lasts for 216 days, ending around May 23. On March 6, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 73% of the time, and overcast or mostly cloudy 27% of the time.

The cloudier part of the year begins around May 23 and lasts for 149 days, ending around October 19. On June 20, the cloudiest day of the year, the sky is overcast or mostly cloudy 70% of the time, and clear, mostly clear, or partly cloudy 30% of the time.

Cloud Cover

clearerclearerclearerclearercloudiercloudier0%10%20%30%40%50%60%70%80%90%100%JanFebMarAprMayJunJulAugSepOctNovDecJun 2070%Jun 2070%Mar 627%Mar 627%Oct 1949%Oct 1949%May 2349%May 2349%overcastovercastmostly cloudymostly cloudypartly cloudypartly cloudymostly clearmostly clearclearclear
The percentage of time spent in each cloud cover band, categorized by the percentage of the sky covered by clouds: clear < 20% < mostly clear < 40% < partly cloudy < 60% < mostly cloudy < 80% < overcast.

Precipitation

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. The chance of wet days in Key West varies significantly throughout the year.

The wetter season lasts 143 days, from May 25 to October 15, with a greater than 37% chance of a given day being a wet day. The chance of a wet day peaks at 59% on September 16.

The drier season lasts 222 days, from October 15 to May 25. The smallest chance of a wet day is 12% on March 20.

Among wet days, we distinguish between those that experience rain alone, snow alone, or a mixture of the two. Based on this categorization, the most common form of precipitation throughout the year is rain alone, with a peak probability of 59% on September 16.

Daily Chance of Precipitation

The percentage of days in which various types of precipitation are observed, excluding trace quantities: rain alone, snow alone, and mixed (both rain and snow fell in the same day).

Rainfall

To show variation within the months and not just the monthly totals, we show the rainfall accumulated over a sliding 31-day period centered around each day in the year. Key West experiences very significant seasonal variation in monthly rainfall.

Rain falls throughout the year in Key West. The most rain falls during the 31 days centered around September 10, with an average total accumulation of 6.1 inches.

The least rain falls around March 29, with and average total accumulation of 1.4 inches.

Average Monthly Rainfall

The average rainfall (solid line) accumulated over the course of a sliding 31-day period centered on the day in question, with 25th to 75th and 10th to 90th percentile bands. The thin dotted line is the corresponding average liquid-equivalent snowfall.

Humidity

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

Key West experiences very significant seasonal variation in the perceived humidity.

The muggier period of the year lasts for 262 days, from March 25 to December 12, during which time the comfort level is muggy, oppressive, or miserable at least 56% of the time. The muggiest day of the year is August 7, with muggy conditions 100% of the time.

The least muggy day of the year is January 30, with muggy conditions 42% of the time.

Humidity Comfort Levels

muggymuggy0%10%20%30%40%50%60%70%80%90%100%JanFebMarAprMayJunJulAugSepOctNovDecJan 3042%Jan 3042%100%Aug 7100%Aug 7Mar 2556%Mar 2556%Dec 1257%Dec 1257%miserablemiserableoppressiveoppressivemuggymuggycomfortablecomfortabledrydry
The percentage of time spent at various humidity comfort levels, categorized by dew point: dry < 55°F < comfortable < 60°F < humid < 65°F < muggy < 70°F < oppressive < 75°F < miserable.

Wind

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in Key West experiences mildly seasonal variation over the course of the year.

The windier part of the year lasts for 210 days, from October 7 to May 5, with average wind speeds of more than 6.4 miles per hour. The windiest day of the year is November 7, with an average hourly wind speed of 7.9 miles per hour.

The calmer time of year lasts for 155 days, from May 5 to October 7. The calmest day of the year is July 29, with an average hourly wind speed of 5.0 miles per hour.

Average Wind Speed

The average of mean hourly wind speeds (dark gray line), with 25th to 75th and 10th to 90th percentile bands.

The predominant average hourly wind direction in Key West is from the east throughout the year.

Wind Direction

0%20%40%60%80%100%JanFebMarAprMayJunJulAugSepOctNovDecwestwestsouthsoutheasteastnorthnorth
The percentage of hours in which the mean wind direction is from each of the four cardinal wind directions (north, east, south, and west), excluding hours in which the mean wind speed is less than 1 mph. The lightly tinted areas at the boundaries are the percentage of hours spent in the implied intermediate directions (northeast, southeast, southwest, and northwest).

Water Temperature

Key West is located near a large body of water (e.g., ocean, sea, or large lake). This section reports on the wide-area average surface temperature of that water.

The average water temperature experiences some seasonal variation over the course of the year.

The time of year with warmer water lasts for 115 days, from June 17 to October 10, with an average temperature above 83°F. The day of the year with the warmest water is August 13, with an average temperature of 86°F.

The time of year with cooler water lasts for 102 days, from December 19 to March 31, with an average temperature below 76°F. The day of the year with the coolest water is February 3, with an average temperature of 73°F.

Average Water Temperature

The daily average water temperature (purple line) with percentile bands, with 25th to 75th and 10th to 90th percentile bands.

Solar Energy

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy experiences significant seasonal variation over the course of the year.

The brighter period of the year lasts for 63 days, from March 21 to May 23, with an average daily incident shortwave energy per square meter above 6.2 kWh. The brightest day of the year is April 28, with an average of 6.9 kWh.

The darker period of the year lasts for 79 days, from November 8 to January 26, with an average daily incident shortwave energy per square meter below 4.4 kWh. The darkest day of the year is December 23, with an average of 3.8 kWh.

Average Daily Incident Shortwave Solar Energy

The average daily shortwave solar energy reaching the ground per square meter (orange line), with 25th to 75th and 10th to 90th percentile bands.

Topography

For the purposes of this report, the geographical coordinates of Key West are 24.555 deg latitude, -81.782 deg longitude, and 0 ft elevation (map ).

The topography within 2 miles of Key West is essentially flat, with a maximum elevation change of 10 feet, and an average elevation above sea level of 2 foot. Within 10 miles is also essentially flat (10 feet). Within 50 miles is also essentially flat (16 feet).

The area within 2 miles of Key West is covered by water (59%) and artificial surfaces (37%), within 10 miles by water (95%), and within 50 miles by water (99%).

Data Sources

This report illustrates the typical weather in Key West, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.

Temperature and Dew Point

There is only a single weather station, Key West International Airport, in our network suitable to be used as a proxy for the historical temperature and dew point records of Key West.

At a distance of 3 kilometers from Key West, closer than our threshold of 150 kilometers, this station is deemed sufficiently nearby to be relied upon as our primary source for temperature and dew point records.

The station records are corrected for the elevation difference between the station and Key West according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.

Please note that the station records themselves may additionally have been back-filled using other nearby stations or the MERRA-2 reanalysis.

Other Data

All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , by Jean Meeus.

All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.

Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.

Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.

Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .

Time zones for aiports and weather stations are provided by AskGeo.com .