Key West Humidity: Florida’s Most Humid Place, Month by Month

Key West is the southernmost point in the continental US and, by a wide margin, the most humid place in Florida. There is no dry season here, no cool nights, and no patch of land to escape the water. Here is what the NOAA records say about an island where even January stays sticky.

In an average year the air in Key West is oppressive on 193 days, 40 more than Miami and twice as many as Jacksonville up north. Comfortable days number just 72, fewer than anywhere else in the state, and even those are not truly dry. I pulled the hourly records from Key West International Airport and counted every day. The finding is blunt: this is not “more humid than the mainland,” it is another level.

Key West, Month by Month

In every other Florida city the dew point line drops into the comfortable zone in winter: Miami to 60°F, the center to 52, Jacksonville to 47. In Key West it never gets there. The driest month is January, and even then the dew point averages 64°F, higher than Miami’s winter low. The island simply has no month you could call dry.

From June through September the line sits at the very top, 75 to 76°F, higher than any mainland metro. Key West is muggier than Miami in summer, and it will not let go in winter the way even the south does. The line runs through the humid and oppressive bands almost all year, dipping only to their edge for a month or two.

When the Air Is Worst

Here the numbers hit the ceiling. In July and August the dew point reaches 75°F on all 31 days of the month, every single day without exception. June is 29, September 28, October 23. Even November and April post 9 to 11 oppressive days, when the center of the state is already at zero. The heavy season here is not five months like the mainland, it is seven to eight.

For a house that means the “dehumidifier season” is barely a season at all. It runs almost year round, with only short pauses in the depth of winter.

A Key West Year at a Glance

Added up, the year splits into 193 days oppressive, 100 humid, and only 72 comfortable. The comfortable share is under a fifth of the year, the smallest green slice of all five cities. More than half the calendar sits past oppressive. Where Tampa and Orlando get nearly half the year pleasant, Key West has almost none.

Why the Island Never Dries Out

The reason is geography, and it is simple. Key West is a tiny island, about four square miles, surrounded by sea on every side: the Gulf to the north, the Atlantic to the south. There is no interior for dry air to hide in. The whole island is the maritime climate, all of it.

And the water around it is the warmest in the state, warm all year. In summer it runs past 85°F, but even in winter it does not cool the way the water along the mainland does. Warm water feeds moisture into the air constantly, which is why the dew point holds in the 60s even in January. The cold fronts that dry out north and central Florida in winter barely reach Key West, 150 miles south of Miami. In effect this is the only truly tropical climate in the continental US: frost-free, and with no dry season at all.

The Night Brings No Relief

As in Miami, the night here is no easier, and really it is harder. In summer the pre-dawn dew point averages 75°F, the afternoon 76°F. There is almost no difference. The air does not clear for an hour: the surrounding sea holds both heat and moisture through the night, and by morning everything is coated in dew and fog. A window opened at night on the island lets in the same swamp as one opened at noon, and the air conditioning and dehumidifier get no break for months.

What This Means for a House in Key West

This is the hardest case in Florida, and it should be treated that way.

Dehumidification here is effectively a year-round job, not a seasonal one. There is no dry window like Tampa’s or Orlando’s, and even the winter pauses are short. Mold is not a risk but a constant: with the dew point above 70°F for most of the year, any unventilated surface goes damp. Bathrooms, closets, and the corners behind furniture need attention all year. If mildew shows up, whether you can clear it yourself or need to bring in a specialist comes down to how far it has spread: here is how to tell.

Then there is salt. The island sits in sea air on every side, and salty moisture is not just mold but corrosion: appliances, electronics, hinges, and air conditioner coils near the water wear out noticeably faster. The target indoors is the same, about 50% relative humidity, but here you have to hold it without a break.

How Key West Compares to the Rest of Florida

Key West is the peak of the state’s humidity, out of reach of the rest: 193 oppressive days against 153 in Miami, 112 in Orlando, and 100 in Jacksonville at the other end. If Jacksonville is the northern, driest edge of the Florida spectrum, Key West is the southern, wettest one. I laid out the full five-city picture here: Florida humidity by the numbers.

What to Do About It

The goal is about 50% relative humidity, and on the island that is a year-round job. The dehumidifier size calculator turns your square footage and humidity into a pint rating, and the best dehumidifiers for Florida covers the units built for this climate. Size up: the load here is higher than anywhere in the state, and nearly without a pause.