textproduct: Key West

KEY MESSAGES

- Deep tropical moisture will linger near the Keys this afternoon, but supporting chances for scattered showers and isolated thunderstorms.

- Drier air associated with a weak early season cold front will arrive tomorrow and into the weekend, resulting in near to below-normal rain chances.

- Increasing northeasterly swell in the wake of the cold front will allow seas to build to 4 to 5 feet by the end of the week, especially in the easternmost Straits of Florida.

DISCUSSION

Issued at 1008 AM EDT Thu Sep 24 2026 Drier conditions are beginning to develop over the Florida Keys. An upper altitude trough that stalled over the southeastern US began to lift northeast yesterday, which started to direct deep tropical moisture away from the Florida Keys. Shower coverage as seen by the KBYX radar is much more sparse compared to the past couple of day. Shower and thunderstorms have been confined to the Florida Straits this morning. Satellite observations from GOES East indicated mostly sunny skies over the northern waters of the Keys. The majority of the cloud cover over the southern waters consisted of cirrus clouds. The dry side of the upper level trough is exerting its influence across the environment. Our morning 12Z KKEY sounding highlights the initial hints that the trough is lifting away. Drier air and northerlies were observed above 500 mb. The environmental PWAT decreased from near record setting values, over 2.4", to below the 90th percentile value for the day. Meanwhile, temperatures are on track to stay below the 90s. Dew points are still in the mid to upper 70s.

Even though drier weather is expected, it is still September. Conditions near the surface will remain muggy and any showers that form will be slow moving in the light winds. Meanwhile, our eyes are on what appears to be a weak frontal boundary making its way south across Florida. It is actually possible that a weak cold front could move south across the Keys Friday to Saturday. If so, look forward to lower dew points to bring in the last weekend of September.

MARINE

Issued at 1008 AM EDT Thu Sep 24 2026 From synopsis: Unsettled weather will persist through the end of the week as deep tropical moisture lingers across the region which will support scattered showers and thunderstorms, mainly in the Straits of Florida. Breezes outside of convection will generally remain light to gentle, variable at times this afternoon, becoming northerly throughout the day. A frontal boundary is expected to push southward across the Keys waters on Friday, resulting in freshening breezes, becoming gentle to moderate in the wake of the front. Winds should gradually slacken a touch over the weekend but will remain out of the north. In addition, seas across the eastern Florida Straits will build at the end of the week and into the weekend due to an incoming 4 to 5 feet northerly swell following the frontal passage.

AVIATION

(12Z TAFS) Issued at 1008 AM EDT Thu Sep 24 2026 VFR conditions will prevail at EYW and MTH. Cloud cover is starting to dissipate near both terminals. Near surface winds will be generally northerly and occasionally variable. While VCSH is absent from the TAF, occasional showers are still possible near the terminals. Winds are on track to become more consistent later in the afternoon.

PREV DISCUSSION

Issued at 449 AM EDT Thu Sep 24 2026

After somewhat of a lull in activity earlier in the evening, scattered showers and a few thunderstorms have redeveloped in the Straits of Florida. However, compared to this time 24 hours ago, this is considerably less activity across our waters. Certainly not for a lack of moisture (2.44" PWATs measured by the 00Z KKEY RAOB), but rather diminishing synoptic-scale lift across the area in connection with an eastward shift in the low to mid-level trough axis over the western Atlantic. Much of the activity is currently focused in the Bahamas and off the east coast of Florida. Current surface obs indicate there is still some residual, albeit weak, cyclonic flow across the area associated with a remnant surface trough which will support at least isolated to scattered showers and a few thunderstorms. As we progress through the day, deep north to northwesterly flow will develop, and finally a weak, early season cold front is expected to pass through the area tonight. Mid-level dry air will surge southward across the Florida Keys by the end of the week as a secondary mid to upper-level trough ejects across the Mid-Atlantic region while broad, deep-layer ridging centered over the Texas coast begins to shift southward. As a result, PoPs will return to near normal or below-normal this weekend. Chance PoPs will be focused in the Straits of Florida where the aforementioned frontal boundary is expected to stall on Friday while chances remain much lower for the Island Chain and waters to our north. Deterministic models still suggest some potential for lower 70s to upper 60s dewpoints along the Keys, particularly Saturday afternoon. Highs will be in the upper 80s over the next couple of days, perhaps a couple of degrees lower this weekend, but it's still too early in the season to expect a truly noticeable temperature swing behind this front. As far as winds are concerned, expect light to gentle west to northwesterly breezes today, freshening to gentle to moderate by tomorrow in the wake of the front. Associated northerly swell will result in building seas of 4 to 5 feet Friday into the weekend in the eastern Straits of Florida off the Upper Keys.

Heading into early next week, the pattern across the CONUS finally looks to become more progressive as the stubborn ridge over the Southern Plains continues to break down and shift further south towards Central America. The upper-level low over the Western Atlantic is expected to deepen and become quite impactful for those along the Northeastern coast. As a result, a return of southwest to southerly flow and associated moisture resurgence is expected across the Florida Keys and surrounding waters by Monday and Tuesday as a secondary mid-upper level trough axis develops over the Southeast extending into the Gulf. This would potentially support near to above normal rain chances once again.

PRELIMINARY POINT TEMPS/POPS

Key West 89 79 89 77 / 20 40 30 20 Marathon 88 78 88 78 / 30 30 30 20

KEY WATCHES/WARNINGS/ADVISORIES

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