Diving Islamorada Between Cold Fronts: Florida Keys Water Temperature and Reef Conditions in December and January

Florida Keys water temperature averages 73.3°F in December and 71.0°F in January at NOAA's Vaca Key station in Marathon. August at the same gauge averages 89.2°F. That's a drop of about 18 degrees, and Islamorada Dive Center (IDC) runs charters year-round from Three Waters Marina at MM 84.5.

What changes in winter is the wind. A cold front can turn a glassy morning into a choppy one, and divers flying in for Thanksgiving, Christmas or New Year's need a plan that bends around it.

Quick Summary: Key Takeaways

• Expect the low 70s at the gauge: IDC's dive-site guide lists a 76°F winter low out on the reef.
• Wear a full wetsuit: single-trip wetsuit rental is $20 if you didn't pack one.
• Fronts pass, then settle: spread your dive days so you can choose the calmer ones.
• Two trips, two depths: the morning deep trip and the afternoon shallow trip suit different groups.

Florida Keys Water Temperature Bottoms Out in the Low 70s by January

January is the coolest month in the Keys, with December and February close behind. In NOAA's Coastal Water Temperature Guide, which NCEI retired in May 2025 with its data left online, the monthly averages for Vaca Key run 77.1°F in November, 73.3°F in December and 71.0°F in January. Key West, at the end of the chain, averages 72.5°F in January.

The Vaca Key gauge sits on the Florida Bay side. Out on the reef sites IDC's boats visit, its own dive-site guide lists 76°F as the winter low.

Bring a full wetsuit. A 3mm full suit is comfortable for most divers at those numbers, but a shorty that felt fine in July will feel thin by the second January dive, and thinner still once a breeze hits wet skin on the ride back to the marina. On a single morning or afternoon trip, wetsuit rental runs $20.

→ scuba and snorkel charters in Islamorada

Cold Fronts Bring Wind, Then Clear Out

Winter weather in the Keys comes in pulses. A front pushes down from the north, the wind picks up behind it, and then it settles back into the calm, clear stretches that make winter diving here worth the flight. The National Weather Service office in Key West notes that the December-to-April dry season gets just shy of 25 percent of the year's rain, usually ahead of cold fronts. So rain is rarely the problem in winter. Wind is.

IDC's captain picks each trip's sites on the day, based on current and sea conditions. That flexibility works best when your own schedule has some too. Divers prone to motion sickness should read up before the trip.

→ tips to avoid seasickness on a Keys dive boat

Calm Winter Mornings Favor the Deep Reef and the Eagle

The settled days after a front are the ones to save for deep diving. IDC's morning trip runs two tanks on Islamorada's barrier reef at 40 to 100 feet, and twice a week it goes to the Eagle wreck instead, at 80 to 115 feet, for Advanced Open Water divers.

The Eagle is a good winter target. IDC's page for the wreck lists winter and spring as its best visibility, and also warns that the site can surge after heavy weather, so with only two wreck mornings a week it pays to build your stay around at least one of them. Sites such as Crocker Wall, a spur-and-groove slope running from 30 feet to nearly 80, are on the same morning rotation.

→ the morning deep reef and wreck dive

The Afternoon Shallow Trip Keeps Holiday Groups Together

Holiday groups are rarely all certified. Grandparents snorkel, a teenager just finished Open Water, an uncle would rather stay on the surface with a mask. The afternoon trip handles that mix: shallow patch reefs at roughly 15 to 30 feet, open to snorkelers from age 5 and certified divers from age 10.

Divers and snorkelers share the same patch of reef, one group a few fathoms below the other. Hens and Chickens and Davis Reef, both Sanctuary Preservation Areas, are among the sites listed for the trip, and the turtles, nurse sharks and schooling tropical fish don't care who's wearing a tank. Snorkelers get their gear included; divers bring their own or rent.

→ the afternoon shallow reef dive and snorkel trip

Spread Your Dive Days Across a Holiday Week

Don't stack them. If you're in Islamorada for five days and want three days of diving, spacing them out gives you more chances to land on the calm mornings after a front.

A multi-trip package fits that kind of week. One payment covers three, four or five trips, redeemable on any morning or afternoon trip during your stay, with a guide in the water on every dive. The redemption code arrives by email at checkout. Two booking details matter over the holidays: IDC recommends booking at least 2–3 weeks ahead in peak season, which it counts as December through April, and it asks for 72-hour notice to cancel around major holidays.

→ multi-trip dive packages

Frequently Asked Questions

Q: What is the water temperature in the Florida Keys in December?

A: NOAA's long-term average at Vaca Key, in Marathon, is 73.3°F for December. IDC's dive-site guide puts the reef's winter low at about 76°F.

Q: Is January a good time to dive the Florida Keys?

A: Yes. NOAA's January averages are 71.0°F at Vaca Key and 72.5°F at Key West, and IDC lists winter and spring as the Eagle wreck's best visibility. Plan around cold fronts by spreading your dive days out.

Q: Do I need a wetsuit to dive Islamorada in winter?

A: For comfort, yes. With winter water in the low to mid 70s, a 3mm full wetsuit beats a shorty for most divers, and single-trip wetsuit rental at IDC is $20.

Plan Your Winter Dives in Islamorada

Send the team your dates, your group's certification levels and how many dive days you're after; the contact form takes custom trip requests as well as questions. From Miami it's roughly an hour and a half down US-1 to Three Waters Resort & Marina, 84001 Overseas Hwy (MM 84.5), Islamorada, FL 33036, where the dive center sits on the marina (islamoradadivecenter.com). Mark which of your days are flexible, because that slack is what lets a cold-front week still include a calm deep morning.

→ Contact Islamorada Dive Center

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