textproduct: Key West

KEY MESSAGES

- Moderate to major saltwater flooding of low elevation streets and lots is likely to continue through this week due to King Tide. Don't drive through flooded roadways. Boaters can expect less clearance under fixed bridges.

- A Coastal Flood Advisory is in effect for the Lower to Middle Keys, and a Coastal Flood Warning is in effect for the Upper Keys.

- Moisture will begin filtering into the area starting today and continuing through the end of the week. This will promote above normal rain and thunder chances, especially Tuesday and onward

DISCUSSION

Issued at 320 AM EDT Mon Sep 28 2026

It has been a quiet overnight across the Keys and surrounding coastal waters. However, not too far away we have been observing showers and thunderstorms developing from around the Isle of Youth (south of Cuba), northwest towards Andros Island. This activity is developing and moving northeast thanks to a rather deep early season trough that is digging across the Gulf waters and into the Yucatan Channel. At the surface we continue to see west to northwest winds at nearly all of our observation platforms. A weak frontal boundary can barely be made out on radar as it lies across the distant Straits of Florida.

This frontal boundary and the aforementioned trough is causing quite the headache this morning with the going forecast. Satellite derived vorticity analysis shows no real indications of a shortwave present except at the 850 mb level. This vort max is developing at the base of the trough and we can see that it's been enough to fire off the showers and thunderstorms as previously described. However, models are not enthusiastic of additional shortwaves developing and ejecting out of this trough today. Meanwhile, the frontal boundary noted across the Straits will slowly lift northward today. This would put the Keys in a southwest flow by the afternoon. This wind direction would tend to favor a reverse cloudline potentially developing. It will come down to how much overhead cirrus we get today. We could have enough of a cirrus shield from the nearby trough to inhibit much growth if a cloudline tries to develop.

As such, made the difficult decision to lower PoPs slightly for today. Time will tell if the right decision was made. Regardless, as we go into tonight and into Tuesday, moisture will only be increasing while the trough begins sharpening across the Gulf basin. This will lead to much better convergence and confluence of both moisture and mass for much of this week. Therefore, still feel fairly confident at above normal rain/thunder chances for the remainder of the period. This active, wet period may also be problematic as a Nor'Easter has been parked north of the Gulfstream and the swells generated by this system is going to back up the Gulfstream over the coming days. Moderate to major saltwater flooding is likely to continue.

MARINE

Issued at 320 AM EDT Mon Sep 28 2026

Coastal flooding is expected to continue through the next several days. This will lead to less clearance under fixed bridges as well as some seawalls and docks becoming overtopped. Although we are past the Full Moon, a powerful Nor'Easter will be backing up the Gulfstream this week and maintaining coastal flooding through the next several days. Meanwhile, a high pressure will move east and reach the Eastern Seaboard on Tuesday, then move offshore and merge with a high pressure across the western North Atlantic. This will allow the newly merged feature to build southward, leading to freshening easterly breezes. Confidence is growing that we will see a period of moderate to fresh breezes, especially Wednesday night through Friday.

AVIATION

(06Z TAFS) Issued at 320 AM EDT Mon Sep 28 2026

VFR conditions will generally be expected. A reverse cloudline may develop this afternoon as surface winds go southwest. This setup would tend to favor the MTH terminal as opposed to the EYW terminal. However, a developing upper level weather system will lie to our west and may eject out occasional shower and thunderstorms. Confidence is too low to include mentions of VCSH/TS at this time.

PRELIMINARY POINT TEMPS/POPS

Key West 88 77 86 77 / 30 50 70 60 Marathon 87 78 86 78 / 20 50 60 60

KEY WATCHES/WARNINGS/ADVISORIES

FL...Coastal Flood Warning for FLZ076.

Coastal Flood Advisory for FLZ077-078.

GM...None.