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

Faro Blanco Marina, Marathon Key.


Franz Marc Frei/Getty Images

Environment-friendly attractions are what draws visitors to Marathon, Florida. Located midway between Key Largo and Key West in the Florida Keys, Marathon is known for its boating and fishing culture that includes deep-sea, reef, and flats fishing. Visitors to Marathon can explore all types of marine life in as well, from stingrays to dolphins to sea turtles, both in nature or one of the island's many marine life reserves.

With an overall average high temperature of 84 degrees Fahrenheit and an average low of 66 degrees, it might just be the weather that makes visitors want to keep coming back multiple times a year. On average, Marathon's warmest month is July while January is the average coolest month, and the maximum average rainfall usually falls in August. The highest recorded temperature in Marathon was a sweltering 104 degrees Fahrenheit in 1998 and the lowest recorded temperature was a very chilly 25 in 1989.

Packing for a vacation to Marathon is pretty simple since the majority of the attractions are 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 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 91 degrees Fahrenheit)
  • Coldest Month: January (low of 64 degrees Fahrenheit)
  • Wettest Month: September (7.72 inches)
  • Driest Month: January (1.61 inches)
  • Best Month for Swimming: August (sea temperature of 86.6 degrees Fahrenheit)

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. Be sure to 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 if 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 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 — Sea temperature of 75.2 F — 2.01 inches
  • January: 69.5 F — Sea temperature of 72.4 F — 1.61 inches
  • February: 71.5 F — Sea temperature of 72.2 F — 2.2 inches

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 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—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 — Sea temperature of 74.1 F — 2.4 inches
  • April: 77.5 F — Sea temperature of 78.1 F — 2.36 inches
  • May: 81.5 F — Sea temperature of 80.9 F — 3.35 inches

Summer in Marathon

The hottest season of the year, summer, sees temperatures in Marathon climb to an average high of 91 degrees Fahrenheit in both July and August, and the humidity levels make the heat almost unbearable. To make matters worse, the Atlantic Hurrican 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, 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 — Sea temperature of 83.4 F — 5.59 inches
  • July: 85 F — Sea temperature of 85.4 F — 4.29 inches
  • August: 85 F — Sea temperature of 86.8 F — 7.01 inches

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—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 — Sea temperature of 85.4 F — 7.72 inches
  • October: 80.5 F — Sea temperature of 82.8 F — 4.76 inches
  • November: 75.5 F — Sea temperature of 78.6 F — 2.83 inches

Average Monthly Temperatures, Rainfall, and Daylight Hours

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 (highs and lows), 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.

  • January: 69.5 F (75 / 64 F) — 1.61 inches (6 days) — 11 hours
  • February: 71 F (77 / 66 F) — 2.2 inches (5 days) — 11 hours
  • March: 74.5 F (79 / 69 F) — 2.4 inches (6 days) — 12 hours
  • April: 77.5 F (83 / 72 F) — 2.36 inches (4 days) — 13 hours
  • May: 81.5 F (87 / 76 F) — 3.35 inches (7 days) — 13 hours
  • June: 84.5 F (90 / 79 F) — 5.59 inches (11 days) — 14 hours
  • July: 85 F (91 / 79 F) — 4.29 inches (12 days) — 13 hours
  • August: 85 F (91 / 79 F) — 7.01 inches (14 days) — 13 hours
  • September: 83.5 F (89 / 78 F) — 7.72 inches (16 days) — 12 hours
  • October: 80.5 F (85 / 76 F) — 4.76 inches (11 days) — 12 hours
  • November: 75.5 F (80 / 71 F) — 2.83 inches (7 days) — 11 hours
  • December: 72 F (77 / 67 F) — 2.01 inches (6 days) — 11 hours