Marathon Temperatures: Averages by Month





The numbers here tell you how hot and cold the weather usually is at Marathon, in the Florida Keys during each month of the year.

The average high and low temperatures are listed below monthly and annually for Boot Key and its neighbors, in both degrees Fahrenheit and Celsius.

Maximums and minimums are only part of the temperature picture. To fill in the rest, there's information on how many days a month get above or below a given temperature.

To find out how often it rises over 70, 80 or 90 °F each month in Marathon, scroll down farther. There are also monthly and yearly counts of days with cool weather.

The first set of high and low temperatures are averages for 2010 to 2019. Everything else here is based on 1981 to 2010 weather.

10-year temperature averages for Marathon, 2010 to 2019
High °F Low °F   High °C Low °C
76 65 January 24 18
79 68 February 26 20
81 69 March 27 21
85 74 April 30 24
88 77 May 31 25
91 80 June 33 26
91 80 July 33 27
92 80 August 33 27
90 79 September 32 26
86 77 October 30 25
82 72 November 28 22
79 69 December 26 21
85 74 Year 29 23
30-year temperature averages for Marathon, 1981 to 2010
High °F Low °F   High °C Low °C
75 64 January 24 18
77 66 February 25 19
79 69 March 26 20
83 72 April 28 22
87 76 May 30 25
90 79 June 32 26
91 79 July 33 26
91 79 August 33 26
89 79 September 32 26
86 76 October 30 24
81 71 November 27 22
77 67 December 25 19
84 73 Year 29 23

Days of Hot Weather in Marathon

Winters are warm and summers hot at Marathon. From May to October, the islands average 81 days with highs in the 90s Fahrenheit. Even so, usually only once every two years does it get as hot as 100 °F (38 °C) in this stretch of Florida Keys.

Days per month in Marathon of at least 70, 80 or 90 °F
  70 °F
21 °C
80 °F
27 °C
90 °F
32 °C
January 24 8 0
February 24 9 0
March 24 16 0
April 30 25 0
May 31 31 3
June 30 30 18
July 31 31 22
August 31 31 24
September 30 30 13
October 31 29 1
November 29 18 0
December 27 11 0
Year 348 268 81

How Often Marathon Has Cool Temperatures

Cool temperatures are rare at Marathon. Just two nights a year on average have lows of 50 °F or less. Temperatures colder than 40 °F (4 °C) are not expected here.

Days per month on average in Key Largo when the minimum temperature drops to 60 or 50 °F or lower
  50 °F
10 °C
60 °F
16 °C
January 1 9
February 0 5
March 0 2
April 0 1
May 0 0
June 0 0
July 0 0
August 0 0
September 0 0
October 0 0
November 0 1
December 1 6
Year 2 24
References

Jay Lawrimore, Ron Ray, Scott Applequist, Bryant Korzeniewski, Matthew Menne. 2016. Global Summary of the Month and Year, Version 1.0. NOAA National Centers for Environmental Information.

NOAA National Centers for Environmental Information. 1981-2010 U.S. Climate Normals. (Data Access. FTP.)

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