Key West in September: Weather, Sea Temperature and the Hurricane Peak

KEY WEST · SEPTEMBER · MILE MARKER 0

Key West in September runs hot, wet and bath-warm. Days average 89.0°F, nights hold at 79.2°F, and the sea off the island sits at 88.3°F. Rain totals 7.24 inches across the month, more than either neighbor gets, and measurable rain falls on 10.2 days. The date that governs the rest is September 10, the statistical peak of the Atlantic hurricane season.

That calendar shapes the trade. September hands you water you can stay in for an hour, evenings that need no jacket, and a free sunset gathering on the waterfront from about 5:30 p.m. It takes back the dry sky and any comfort in a non-refundable reservation. Where to sleep, how to drive the Overseas Highway and what the island offers year-round sit in our Key West guide, and the Florida calendar sets this month against the other eleven.

On this page

• Average high, low and rain days in SeptemberKey West weather in September
• Sea temperature for swimming88.3°F, and what it feels like
• Crowds, the lodging tax and when to bookHow busy September runs
• Things to do on a wet September dayFort Zachary Taylor, Hemingway Home, Dry Tortugas
• A two-day plan built around the heatThe September itinerary, hour by hour
• September against August and OctoberHow the three months compare
• Is September a good month to go?The verdict, for and against
• Key West in AugustThe month before

Getting to the island does not change with the month, but in September it is worth knowing both ways in. Miami to Key West is about 155 miles and close to four hours by road without stops, six to eight with them, running down the all-electronic Homestead Extension to Florida City and then US-1. Key West also has its own airport, EYW, and flying in removes the drive from the equation entirely.

Key West weather in September: average highs, lows and rain days

Every figure here comes from NOAA NCEI’s 1991–2020 monthly normals for station USW00012836, a real thermometer at Key West International Airport, not a reanalysis grid cell averaged over open water. September at that station averages a high of 89.0°F and a low of 79.2°F, with 7.24 inches of precipitation. Both neighboring months are drier: August records 5.37 inches, October 5.67.

Measurable rain shows up on 10.2 days in an average September, roughly one day in three, and 1.9 of those days deliver an inch or more. Divide the month’s total by its wet days and you get about 0.7 inch each, so the two heavy days carry a large share of the water. In practice most wet days cost an hour or two outdoors. Two of them can cost an afternoon, and you plan the indoor option before you need it.

Day and night are only 9.8°F apart, so the island never really cools after dark. Nothing warm goes in the bag. What does go in: a dry second shirt for the walk back to the room, reef-safe sunscreen because you will be at water level for hours, and a rain shell light enough to fold into a pocket for those 10.2 days.

September 15 brings 12 hours 19 minutes of daylight, sunrise at 7:12 a.m. and sunset at 7:31 p.m. local time. The Sunset Celebration at Mallory Square starts about two hours before sunset and carries on until dusk has faded. Mid-month that puts people on the waterfront from roughly 5:30 p.m., with dinner pushed back to a properly late hour.

Can you swim in Key West in September? Sea temperature and what it feels like

Open-Meteo’s marine series puts the sea surface off Key West at 88.3°F in September, averaged over 2015 to 2024. One caveat travels with that number, and it matters: it is the mean of daily maxima, so it runs a shade warmer than a 24-hour average of the same water would. Early morning swims are cooler than 88.3°F suggests.

At that temperature there is no gasp on entry and no reason for a rash guard beyond the sun. Snorkelers can stay down until their fingers wrinkle, and children do not turn blue at the edges. The catch is that water within a degree of the 89.0°F air gives no cooling: the swim is a pleasure and not a cool-down, and the shade behind the beach does more for your body temperature than the sea does.

We found no wind or wave series for September off Key West, so we give no figures for either. What the calendar does carry is the storm window. NOAA’s National Hurricane Center runs the Atlantic season from June 1 to November 30, with the statistical peak on September 10 and most activity between mid-August and mid-October. Check the tropics the week before you fly, and again the morning you set out.

How busy is Key West in September? Crowds, the lodging tax and booking windows

No occupancy series and no month-by-month room rates turned up in our sources, so we rank no month of the Key West year by price. What we can date is the storm calendar: September contains the September 10 peak, and that one fact moves bookings more than anything else on the island’s schedule. Cruise arrivals are not capped either. Key West voters approved three limits in November 2020, including a cap of 1,500 disembarking passengers a day, and SB 1194 nullified them, written to apply retroactively.

Fix the boat before you fix anything else. The Yankee Freedom III to Dry Tortugas sells out weeks ahead through the year, and the operator’s own advice is to reserve at least a month in advance. Rooms are a different question, and we could not verify how far ahead September fills in Key West, so we give no lead time we cannot support. Reserve the crossing, then build the two days around its 8 a.m. departure.

Your room bill carries a Monroe County transient rental tax of 5.0%, filed and paid alongside the 6% state sales tax, so 11% lands on top of the nightly rate whether the booking page shows it upfront or not. Parking is its own line item: city street meters run $3.00 an hour, the Key West Bight lot $5 an hour or $40 a day, the Old Town Parking Garage $6 an hour or $48 a day plus tax, the Mallory Square lot $7 an hour or $48 a day with a ten-hour maximum.

One upgrade genuinely changes this month, and it is not the room category: pay the difference for a rate you can cancel. A week straddling the 10th is the week you may need to move, and only a cancellable booking lets you move it without arguing. The second-best use of money is a bed inside Old Town, close enough to walk everywhere. That retires the $48-a-day garage for the whole stay.

Things to do in Key West in September: Fort Zachary Taylor, the Hemingway Home and Dry Tortugas

September gives the water and takes the dry sky. The sea holds 88.3°F, within half a degree of August and 4.1°F above October, so this is the month for snorkel sessions measured in hours and for a Dry Tortugas crossing spent mostly in the shallows rather than inside the fort.

Fort Zachary Taylor Historic State Park holds the beach most people rate the island’s best, and you can reach it on foot from Old Town: $2.50 walking or cycling in, $4.50 for a single-occupant vehicle, $6.00 per car for up to eight people plus a $0.50 county surcharge each. Dry Tortugas National Park lies 70 miles west with no road or bridge to it. The Yankee Freedom III leaves at 8 a.m. with check-in before 7:30, and the 2026 adult fare of about $250 covers park entry, snorkel gear, breakfast and lunch.

September leaves the fees alone and changes the air around them. The park gate opens at 8 a.m. and closes at sundown, 365 days a year, with the fort itself shutting at 5 p.m., so a 7:31 p.m. sunset gives you a long beach day that the 89.0°F afternoon pushes into the pines behind the sand. On one of the month’s 10.2 wet days, the Ernest Hemingway Home and Museum is the reliable fallback: walk-in visits 9 a.m. to 5 p.m. daily, $19 adults, $7 children, free under six, with resident cats the museum traces to Snow White, the novelist’s polydactyl pet, by its own account.

Free fills the gaps. The Duval Loop bus costs nothing and calls at 18 stops around Old Town, though published schedules disagree: one source gives every 20 minutes from 8 a.m. to 10 p.m., another every 30 minutes from 6 a.m. and then every 15 until midnight, so read the stop sign when you board. It does not serve the airport. The Sunset Celebration at Mallory Square is free every night of the year, weather permitting. And Mile Marker 0, at Whitehead and Fleming, marks the southern end of a road running about 2,370 miles north to Fort Kent, Maine.

Key West in September: a two-day itinerary

Day one runs on the 7:12 a.m. sunrise. Coffee early, then the 8 a.m. gate at Fort Zachary Taylor, $2.50 if you walk in, and the water at 88.3°F while the sand is still bearable. Out by noon: Old Town is flat, compact and the largest wooden historic district in North America, so the middle hours go under awnings and indoors. Be at Mallory Square around 5:30 p.m., two hours before the 7:31 p.m. sunset, and eat afterward.

Day two belongs to the boat if you booked it: check-in before 7:30 a.m., away at 8, 70 miles west and back. If the forecast turns, keep the day on the island. The Hemingway Home takes walk-ins until 5 p.m., the free Duval Loop covers the wet blocks between stops, and key lime pie repays a rainy hour: Key West’s own since the late nineteenth century, Florida’s official pie since 2006, and built on sweetened condensed milk because fresh milk and refrigeration were scarce down here before the 1930s.

Key West in September vs August and October

Side by side, September sits between its neighbors on temperature and above both on rain. Days average 89.0°F against August’s 90.6 and October’s 85.8, nights 79.2 against 80.5 and 76.8. Rainfall is where the month separates itself: 7.24 inches, against 5.37 in August and 5.67 in October, spread over 10.2 wet days, against 9.1 and 7.6. The sea barely registers the turn, 88.8°F in August and 88.3 in September, before dropping to 84.2 in October.

Shift four weeks later and you buy 2.6 fewer wet days, 1.57 inches less rain and an afternoon 3.2°F cooler. You pay 4.1°F of sea warmth for it, which is the gap between water that feels like a bath and water that feels like a swim. October also stays inside the hurricane season, since most activity runs to mid-October and the season itself ends November 30, so the calendar risk drops without vanishing.

Is September a good time to visit Key West?

Yes for swimmers. If your Key West is water at 88.3°F, a snorkel that lasts an hour and an evening that needs no jacket at nine o’clock, the month delivers all three, and the price is 10.2 wet days plus a booking you may have to move. No for anyone locked into fixed non-refundable dates around the 10th, and no for anyone who wants to walk Old Town at midday in comfort.

If the answer is no, October is the shift to make: 85.8°F days, 7.6 wet days, 5.67 inches of rain and a sea still at 84.2°F, past the statistical peak though not out of the season. Going the other way, August trades 1.6°F of extra afternoon heat for 1.87 inches less rain, and our August page takes that month apart.

Among the three, September is the one that holds August’s water within half a degree while shaving 1.6°F off its afternoons, which is why the swimming reads better here than the rain gauge suggests.

The last word

Decide the rate before you decide the room: in a month built around the 10th, a booking you can cancel is worth more than a better view. Then think about the drive, if you are driving. There is no safe place to stop on the Seven Mile Bridge itself, but the old bridge alongside carries a restored two-mile span open to walkers and cyclists, with a car park at the Marathon end and Pigeon Key halfway across. Two miles of open concrete under an 89.0°F sky is a morning errand. Do it on the way down, before the heat settles in.

Sources & data for this guide

• September normals, rain days and the August and October columns · NOAA NCEI 1991–2020 monthly normals, station USW00012836 (Key West International Airport) · checked Sep 23, 2026
• Sea surface 88.3°F, mean of daily maxima 2015–2024 · Open-Meteo Marine API · checked Sep 23, 2026
• Daylight, sunrise and sunset for September 15, converted to America/New_York · sunrise-sunset.org · checked Sep 23, 2026
• Hurricane season dates and the September 10 peak · NOAA National Hurricane Center · checked Sep 23, 2026
• Monroe County 5.0% transient rental tax with the 6% state sales tax · Florida Department of Revenue, form DR-15TDT · checked Sep 23, 2026
• Fort Zachary Taylor fees and hours · Florida State Parks · checked Sep 23, 2026
• Hemingway Home hours, admission and the Snow White lineage, which is the museum’s own account · hemingwayhome.com · checked Sep 23, 2026
• Dry Tortugas access and the 2026 Yankee Freedom III fare · National Park Service and drytortugas.com · checked Sep 23, 2026 · fares change
• Parking meters, garage and lot rates · City of Key West Parking Department · checked Sep 23, 2026 · rates change
• Duval Loop stops and timetable · City of Key West and Car-Free Key West · checked Sep 23, 2026 · our sources disagree on frequency and span, so we give the range and send you to the stop sign
• Sunset Celebration nightly schedule · sunsetcelebration.org · checked Sep 23, 2026
• Cruise referendum of November 2020 and SB 1194 · Florida Politics and Seatrade Cruise · checked Sep 23, 2026
• Mile Marker 0 and the distance to Fort Kent, Maine · Atlas Obscura and Key West Travel Guide · checked Sep 23, 2026 · sources give 2,369 or 2,390 miles, so we round to the order of magnitude
• We found no occupancy series and no monthly room-rate series for Key West, so we crown no month cheap or expensive. We also could not verify wind or wave figures for September, and none appear above.

To plan your stay

• Things to Do in Key West: Hours, Prices, Hemingway House and the Dry Tortugas Ferry
• Where to Stay in Key West: Old Town, New Town and What Parking Costs
• Key West Airport to Old Town: Transfers, Parking and the Drive from Miami
• What to Know Before You Go to Key West: Parking, the Free Duval Loop, Sunset and the Dry Tortugas Ferry

Nearby places

• Everglades National Park: The Complete Visitor's Guide
• Big Cypress National Preserve: Dark Sky Park, Swamp Buggies and the $100 ORV Permit
• Dry Tortugas National Park: Ferry, the $15 Entrance Fee and Camping on Garden Key