Summertime in Marathon, Florida
Summer in Marathon, Florida is warm, tropical, and full of adventure. With long sunny days, warm ocean water, and endless opportunities for boating, snorkeling, and island exploring, it’s one of the most exciting times of the year to visit the Keys.
Here is everything you need to know about summer weather, activities, events, and FAQs - all in one easy, vacation-friendly blog.
Average Summer Temps & Climate
June: High 89°F / Low 79°F
July: High 90°F / Low 80°F
August: High 90°F / Low 80°F
Humidity Index
Typically 75–78%, higher than spring. Expect classic tropical humidity - sunscreen and hydration are musts
Rainfall
Afternoon showers and brief tropical bursts are common. Average rainfall increases into summer. Expect 4–5+ inches per month, depending on storms. Most rain passes quickly, with sunshine returning soon after
Water Temperatures
June: ~82–84°F
July: ~85°F
August: ~86°F
Summer brings the warmest ocean water of the year, perfect for snorkeling, sandbars, and endless swimming.
Top Things to Do in Marathon During the Summer
Snorkeling & Reef Adventures
With the water warm and visibility high, summer is prime time to explore:
- Sombrero Reef
- Coffins Patch
- Looe Key (a must!)
Expect vibrant coral, tropical fish, turtles, rays, and unforgettable underwater colors.
Boating & Sandbar Days
Warm water + sunny skies = perfect boating weather. Popular outings include:
- Renting a boat for the day
- Visiting the famous Marathon Sandbar
- Cruising to secluded coves
- Island hopping the Middle Keys
Bring a cooler, floaties, and enjoy the Keys lifestyle.
Fishing (All Types!)
Summer fishing in Marathon is excellent, with a variety of species in season:
- Dolphin (Mahi Mahi)
- Tarpon
- Snapper
- Grouper
- Tuna
Offshore, reef, and bridge fishing are all productive this time of year.
Summer Seasonal Events
Beach Kids' Fishing Derby
(June)
Lower Keys Dolphin Tournament
(June)
Islamorada Independence Day
(July)
Underwater Music Festival
(July)
Is Summer TOO Hot in Marathon?
It’s warm and tropical — expect highs near 90°F and humid days. But ocean breezes, endless water activities, and indoor dining keep things comfortable.
Does It Rain Every Day in Summer?
Short afternoon showers are common, but they usually pass quickly. Mornings are typically sunny and ideal for boating or beach adventures.
Is Summer Good for Snorkeling & Fishing?
Summer is excellent for both. Warm, clear water is ideal for snorkeling, and many top fish species are in season.
Is the Water Warm Enough to Swim In?
Absolutely — summer brings the warmest ocean temps of the year, often mid-80s.