Weather in Marathon, Florida: Climate, Seasons, and Average Monthly Temperature

Faro Blanco Marina, Marathon Key.


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Located midway between Key Largo and Key West in the Florida Keys, Marathon, Florida, is known for its boating and fishing culture, which includes deep-sea, reef, and flats fishing. Visitors to Marathon can explore all types of marine life as well—including stingrays, dolphins, and sea turtles—both in nature and in the island's many marine life reserves.

With an overall average high temperature of 84 degrees Fahrenheit (28.8 degrees Celsius) and an average low of 66 F (18.8 C), the weather keeps visitors coming back multiple times a year. On average, Marathon's warmest month is July while January is the coolest month, and the maximum average rainfall usually comes in August.

Packing for a vacation to Marathon is pretty simple since the majority of the attractions here are found outdoors. Bring your bathing suit to swim with the dolphins, relax on the beach, take up a new watersport, or just work on your tan. Of course, you'll also need to bring resort casual clothing for dining out or strolling the streets during the night and evening hours. The dress code in most of the Florida Keys is cool, casual, and comfortable—island style, so nothing too fancy is necessary. 

Fast Climate Facts

  • Hottest Month: July and August, high of 90 degrees Fahrenheit (32 degrees Celsius)
  • Coldest Month: January, low of 65 degrees Fahrenheit (18 degrees Celsius)
  • Wettest Month: September, 7.73 inches
  • Driest Month: January, 1.61 inches
  • Best Month for Swimming: August, sea temperature of 86.6 degrees Fahrenheit (30.3 degrees Celsius)

Hurricane Season

The Florida Keys are not often affected by hurricanes, although they were hit pretty hard during 2017's Hurricane Irma. However, the weather during the Atlantic hurricane season, which runs from June 1 through November 30 each year, is quite unpredictable, and there is always a possibility of getting hit by a tropical storm throughout the summer and fall. Keep your eyes on the forecast and perhaps even sign up for mobile severe weather alerts during your trip to make sure you're aware of any incoming tropical storms while you're visiting Marathon this time of year.

Winter in Marathon

The Florida Keys experience some of the best weather from December through May each year, but the winter is the driest and coldest season in Marathon. With an average temperature of a pleasant 71 degrees Fahrenheit (21.6 degrees Celsius) and around two inches of rainfall per month, winter is a great time to enjoy the warm sandy beaches and the 72-degree water temperatures. However, winter is also the peak of tourist season for the Florida Keys, so you can expect higher rates on hotels and airfare and may need to make reservations at most of the city's restaurants in advance of your trip.

What to pack: Since the temperature doesn't change much from day to night and the weather's generally nice all season long, you won't have to worry about packing a variety of extra clothing. Just remember to bring your bathing suit and your casual dinner wear.

Average Air and Sea Temperatures and Rainfall by Month

  • December: 72 F (22.2 C); sea temperature of 75.2 F (24 C); 2.01 inches of rain
  • January: 69.5 F (20.8 C); sea temperature of 72.4 F (22.4 C); 1.61 inches of rain
  • February: 71.5 F (21.9 C); sea temperature of 72.2 F (22.3 C); 2.2 inches of rain

Spring in Marathon

The best time to visit the Florida Keys is in the spring when temperatures rise to a warm-yet-manageable seasonal average of 78 degrees Fahrenheit (25.5 degrees Celsius) and tourist crowd sizes die down from their winter peak. Although spring is a little wetter than winter, the rainy season doesn't really start until the end of May—which gets 3.35 inches compared to March's 2.4 inches—so you'll have plenty of chances to enjoy taking a dip in the warm ocean waters.

What to pack: As with the winter, you'll just need to remember to pack the essentials like a bathing suit, shorts, shirts, and other linen or light-material clothing. However, you may also want to stock up on sunscreen if you plan to spend a lot of time on the beaches as the UV index rises significantly over the season.

Average Air and Sea Temperatures and Rainfall by Month

  • March: 74.5 F (23.6 C); sea temperature of 74.1 F (23.4 C); 2.4 inches of rain
  • April: 77.5 F (25.2 C); sea temperature of 78.1 F (25.6 C); 2.36 inches of rain
  • May: 81.5 F (27.5 C); sea temperature of 80.9 F (27.1 C); 3.35 inches of rain

Summer in Marathon

The hottest season of the year, summer, sees temperatures in Marathon climb to an average high of 91 degrees Fahrenheit (32.7 degrees Celsius) in both July and August, and the humidity levels can make the heat almost unbearable. To make matters worse, the Atlantic Hurricane Season starts in June, which is when the region gets most of its rainfall. Fortunately, though, June and July are relatively drier than August and early September, so you should still have plenty of sunny days to enjoy in the Keys this summer.

What to pack: If you're traveling to Marathon in the early part of the season, the less clothing you bring, the happier you'll be. Later in the season, you'll want to bring along waterproof shoes, a raincoat, a rain hat, a rain suit, and an umbrella in case you get caught in a sudden summer storm.

Average Air and Sea Temperatures and Rainfall by Month

  • June: 84.5 F (29.1 C); sea temperature of 83.4 F (28.5 C); 5.61 inches of rain
  • July: 85 F (29.4 C); sea temperature of 85.4 F (29.6 C); 4.28 inches of rain
  • August: 85 F (29.4 C); sea temperature of 86.8 F (30.4 C); 6.99 inches of rain

Fall in Marathon

The rainy season only intensifies as fall arrives in the Florida Keys. September is the wettest month of the year, accumulating nearly eight inches of rainfall over 16 days, and while October is a little drier, it still receives nearly five inches over an average of 11 days. However, you can typically expect fewer storms and cooler weather later in the fall, making it a great time to visit. In fact, November—with average low and high temperatures ranging from 71 to 80 degrees Fahrenheit (21 to 27 degrees Celsius)—only sees about seven days and a little under three inches of rainfall throughout the month.

What to pack: It's best to avoid the Florida Keys in September and October, but you'll definitely need to pack rain gear if you travel to Marathon during the first part of fall. In November, on the other hand, you should be fine with just bringing an umbrella and your beach gear.

Average Air and Sea Temperatures and Rainfall by Month

  • September: 83.5 F (28.6 C); sea temperature of 85.4 F (29.6 C); 7.73 inches of rain
  • October: 80.5 F (26.9 C); sea temperature of 82.8 F (28.2 C); 4.78 inches of rain
  • November: 75.5 F (24.1 C); sea temperature of 78.6 F (25.8 C); 2.82 inches of rain

Although only slightly different, the seasonal changes in the weather in Marathon can affect the quality of your trip. As a result, it's helpful to know the average temperature, rainfall expectations, and amount of daylight hours each month to plan your perfect Florida vacation. However, you should also be sure to check the weather forecast before and during your trip to stay up-to-date on current and expected conditions in the Keys.

Average Monthly Temperature, Rainfall, and Daylight Hours
Month Avg. Temp. Rainfall Daylight Hours
January 70 F 1.6 inches 11 hours
February 71 F 2.2 inches 11 hours
March 75 F 2.4 inches 12 hours
April 78 F 2.4 inches 13 hours
May 82 F 3.4 inches 13 hours
June 85 F 5.6 inches 14 hours
July 85 F 4.3 inches 13 hours
August 85 F 7.0 inches 13 hours
September 84 F 7.7 inches 12 hours
October 81 F 4.8 inches 12 hours
November 76 F 2.8 inches 11 hours
December 72 F 2.0 inches 11 hours