textproduct: Key West

KEY MESSAGES

-Light to gentle west to northwest breezes will continue to veer to the north to northeast by tonight.

-Light winds and a moist air mass could promote patchy fog for the island chain this morning, but this is more likely across the nearshore waters north of the island chain. Impacts along the island chain are not expected.

-The best chances for rain today will be during the early morning hours, and weather should be mostly dry as we head into the weekend.

DISCUSSION

Issued at 450 AM EST Fri Dec 19 2025 Most of the excitement occurred at the start of the overnight shift as showers and thunderstorms across central and eastern portions of the Florida Straits were ongoing. There werent any rainfall observations along the island chain, but this may be due to the sparse nature of automated observation sites. MRMS suggests there may have been a few hundredths of an inch of rain in some locations along the Middle and Upper Keys. Nighttime Microphysics from GOES-19 shows a broken swath of cloud cover across the area, but surface observations at both Key West and Marathon International Airports have not reported persistent cloud cover. This tells us that these clouds are higher in altitude through the mid and upper levels, and this is important for later in this discussion. Temperatures have generally been in the mid 70s with dew points just behind that, and a line of showers and thunderstorms over our western waters is progressing eastward.

In the very short term, the main weather concern is marine fog, particularly over Florida Bay and the Bayside waters on the north side of the island chain. Sea surface temperatures in that area are near 72F to 74F. The dew point depression across the southern tip of the peninsula, and along the island chain, is anywhere from 0F to 3F, indicating that the air mass is nearly saturated. Ideally, we would like the water temperatures to be just a little bit cooler for more of a slam dunk fog event, but these conditions may lead to some patchy marine fog. Hourly MOS guidance available for our aviation sites point to a very low probability of reduced visibility this morning (less than 10 percent chance), which is usually indicative of fog. There are two caveats with this fog forecast. Earlier we mentioned that there is a swath of mid to upper level clouds across the area, and this includes the area where we suspect fog may form. While satellite-derived products do help us see fog when it occurs, these clouds will obstruct the view of the sea surface. There are also no observation platforms across Florida Bay that report visibility, so if fog occurs under these marginal conditions, we may not get any ground truth to confirm it. Regardless, we will keep patchy fog in the forecast for this morning even with the uncertainty that exists.

For today, a weak boundary sagging down the Florida peninsula will not mean too much for our sensible weather. Breezes will continue to veer from the southwest to west this morning to the northwest to north later. Low level moisture ahead of the front seems ample enough to encourage some shower activity near the island chain. 10 percent PoPs almost seems a little too low, but 20 percent seems a little too high. Opting to advertise 10 percent in the zone forecast with the disclaimer here that its more of a higher 10 percent. With the above-normal moisture in the lower levels coupled with slight veering of the winds, showers are going to happen somewhere in the CWA, its just a matter of where. This front, or what is left of it, will lift out of the area tonight, and higher pressure will build in. This will help to keep weather over the weekend calm and quiet with temperatures just a couple of degrees warmer than average.

Over the start of the new work week, low level ridging will amplify along the eastern U.S. and guidance points to a change in the sensible weather, particularly surface winds. With the northeasterly flow, this may be a backdoor front approaching the area. The tightening surface gradient could lead to breezy, or even windy, conditions from Monday through Wednesday. Speed convergence coupled with low level moisture could produce a few light showers as well, so opting to throw in low end PoPs just in case. Santas reindeer are cleared to fly in these elevated winds, so we do not have any concerns with regard to the holiday.

MARINE

Issued at 450 AM EST Fri Dec 19 2025 There are no watches, warnings, or advisories in effect for the Florida Keys local waters. From synopsis, a weak front will push through the Florida Keys coastal waters today, and our generally light to gentle westerly breezes this morning will veer to the north by tonight. Modestly freshened breezes are expected for the weekend in its wake. Another high building over the Eastern Seaboard will support fresh to strong breezes for early to mid week.

AVIATION

(06Z TAFS) Issued at 450 AM EST Fri Dec 19 2025 VFR conditions are expected to prevail at both EYW and MTH terminals through the TAF period. A weakening frontal boundary is expected to pass through the Keys sometime late today or this evening. Latest guidance shows some weak convection out ahead of the front with the potential for a passing shower around 19/18z. However, due to the uncertain nature in the strength and placement of this activity, VCSH was left out of the TAF for now. Winds will become northwest to north between 5 to 10 knots this afternoon before further shifting to the north overnight.

CLIMATE

On this day in 2016, the daily record warm low temperature of 77F was recorded in Key West. Temperature records for Key West date back to 1872.

PRELIMINARY POINT TEMPS/POPS

Key West 82 69 79 71 / 10 0 0 10 Marathon 79 69 78 72 / 10 0 10 10

KEY WATCHES/WARNINGS/ADVISORIES

FL...None. GM...None.