textproduct: Key West

KEY MESSAGES

- Moderate to major saltwater flooding of low elevation streets and lots is likely to continue over the next few day or so due to King Tide. Don't drive through flooded roadways. Boaters can expect less clearance under fixed bridges.

- A Coastal Flood Warning is in effect for the Upper Keys, particularly along the sounds, bay side of Key Largo. A Coastal Flood Advisory is in effect for the Middle and Lower Keys.

- A wet pattern is expected for the next several days across the Keys. This will maintain above normal rain and thunder chances through at least Thursday.

AVIATION

(18Z TAFS) Issued at 256 PM EDT Tue Sep 29 2026

Widely scattered to numerous SHRA and occasional TSRA will move across the region through this evening with occasional MVFR/IFR restrictions, especially during pockets of heavier rainfall. There may be a brief lull in the late evening and overnight hours before additional activity develops again Wednesday morning through the end of the period. Winds will remain out of the SE through tonight but will shift to a more easterly direction on Wednesday at 10-15 kts and occasional gusts to 20 kts. While VFR conditions will generally prevail outside of convection, elevated rain chances will maintain potential of restrictions most times throughout the period.

UPDATE

Issued at 1129 AM EDT Tue Sep 29 2026

Deep tropical moisture continues to surge into the Florida Keys as upper air analysis shows troughing with a slight positive tilt extending into the Yucatan region and western Caribbean and a mid/upper level anticyclone positioned in the subtropical Atlantic southeast of Bermuda. Meanwhile, a 55-65 kt jet streak analyzed at 250 mb is streaming across the Florida peninsula, providing plenty of divergence aloft across the region and this will generally remain in place through the remainder of the day as the upper trough axis remains to our west. Given the favorable forcing for ascent and deep moisture with PWATs around 2 inches or more, rounds of scattered to occasional numerous showers and embedded thunderstorms will drift in a general northeastward direction across the Island Chain and surrounding coastal waters the remainder of the day. The 12Z KEY RAOB shows good moisture in the mid and upper levels with some dry air and inhibition in the low levels, likely related to the more stable and post-convective environment that was in place earlier. Forecast soundings through the remainder of the day do maintain somewhat drier air in the lower levels, which may be indicating some Cuban shadow influence from low level southerlies. However, the aforementioned dynamics should be able to overcome these potential limiting factors enough to still support likely PoPs so will continue with the inherited forecast. With this overall environment of deep moisture and ascent, coupled with the background of elevated tide levels, the main concern will be locally heavy rainfall and flooding, especially during high tide cycles and in areas that typically experience King Tide flooding. Otherwise, dewpoints have returned to the mid 70s area-wide and with highs reaching the mid/upper 80s later today, the more typical warm and humid feel to the air in late September is back after the recent multi-day slight taste of fall.

DISCUSSION

Issued at 436 AM EDT Tue Sep 29 2026

An incredibly messy but dynamic weather pattern is setting up across the Florida Keys this morning. Let's break it down. At the surface we have weak ridging occurring which is leading to chaotic, but light surface winds. In the lower levels the ridge axis of an Atlantic Ridge lies just to our south but is steadily marching northward. In the mid and upper levels we have a pronunced, deep trough that extends from near the Great Lakes Region well south across the Gulf Basin and into the western Caribbean. This feature is providing broad cyclonic flow aloft as well as the occasional shortwave that has ejected northeastward.

The aforementioned Atlantic Ridge axis will continue lifting northward today. As it does, it will help to align our surface winds more out of the east to southeast. In addition, the steering flow more become more southerly, allowing for better moisture transport from the western Caribbean ahead of the mid/upper level trough. Thus far the trough has resided to our west with a plethora of convection erupting throughout the last day or so. However, as this activity tries to move northeast and away from the trough, it has encountered more stable and relatively drier air. This has kept much of the precipitation from reaching the Florida Keys.

Today should be the transition point for the Keys. The mid/upper level trough will slowly edge eastward today allowing for a better alignment of moisture and lift. The fly in the ointment is the low level ridge axis lifting northward. This will cause a southerly wind below 700 mb and could bring in low level dry, warm air advection. This may counter the increasing moisture aloft, leading to an overall lower coverage of showers and thunderstorms for today. Hi-res CAMs continue to advertise that we will have enough synoptic forcing to overcome the more mesoscale effects. Time will tell if this actually happens.

Once this feature sets in, we can expect multiple days of wet, active weather through at least Thursday. Thereafter, a ridge out across the Atlantic will shift further to the west and retrograde the mid/upper level trough into the Bay of Campeche. This would lower our rain chances back closer to normal with a moist east to southeast flow.

MARINE

Issued at 259 PM EDT Tue Sep 29 2026

A high pressure system across the eastern third of the U.S. will steadily shift east into the western Atlantic through tonight. As it does, east to southeast winds will remain in place. Thereafter, this high will shift further offshore and merge with an existing high pressure across the subtropical Atlantic and subsequently build through the remainder of the week. This will promote freshening breezes with an increasing likelihood of moderate to fresh breezes beginning Wednesday, continuing through late week. There is a good chance that marine Cautions may be required for portions of Keys waters at that time, and Advisories cannot be ruled out. In addition, a very wet pattern will remain across the Keys over the next few days, resulting in periods of scattered to numerous showers and thunderstorms.

AVIATION

(18Z TAFS) Issued at 256 PM EDT Tue Sep 29 2026

Widely scattered to numerous SHRA and occasional TSRA will move across the region through this evening with occasional MVFR/IFR restrictions, especially during pockets of heavier rainfall. There may be a brief lull in the late evening and overnight hours before additional activity develops again Wednesday morning through the end of the period. Winds will remain out of the SE through tonight but will shift to a more easterly direction on Wednesday at 10-15 kts and occasional gusts to 20 kts. While VFR conditions will generally prevail outside of convection, elevated rain chances will maintain potential of restrictions most times throughout the period.

KEY WATCHES/WARNINGS/ADVISORIES

FL...Coastal Flood Warning until 7 AM EDT Wednesday for FLZ076.

Coastal Flood Advisory until 7 AM EDT Wednesday for FLZ077-078.

GM...None.