textproduct: Key West

KEY MESSAGES

- A late-season cold front will move through the Florida Keys overnight, supporting an elevated chance of showers and a slight chance of thunderstorms.

- Fresh to strong breezes are expected in the wake of the front. A Small Craft Advisory is effect for all Keys coastal waters.

- There is low confidence in the rain and thunder chances for Thursday and Friday.

DISCUSSION

Issued at 930 PM EDT Mon Apr 20 2026 CIMSS MIMIC total precipitable water product highlights a tight moisture gradient associated with a frontal boundary slowly nudging southward towards the Florida Keys at this late evening hour. The 00z evening sounding at KEY highlighted generally stable low levels, a chaotic wind field, and a relatively dry boundary layer. With that said, deeper moisture over the South Florida Mainland is progressing southwestwards. Portions of the Upper Keys received quite a bit of rainfall this evening, with radar- estimated totals approaching 3-4" in select island communities between North Key Largo and Ocean Reef. Meanwhile, the Lower and Middle Keys have remained dry thus far tonight.

Overnight, the aforementioned frontal boundary will continue to slowly progress southward. Nearly all available Convective Allowing Model (CAM) guidance supports additional showers being triggered in portions of the Upper Keys between 03-06z, with the associated outflow zippering additional showers across most of the Island Chain. This seems plausible, albeit probably a bit overdone in terms of coverage and intensity. As is often the case this time of year, decreasing baroclinicity this far south has slowed the momentum of the front. Due to this, did elect to nudge rain chances upward for the first part of Tuesday as the front likely lingers in the vicinity of portions of the Keys. Other than that adjustment, no changes proposed for this late evening update cycle.

MARINE

Issued at 930 PM EDT Mon Apr 20 2026 A Small Craft Advisory is in effect for all Florida Keys marine zones. From synopsis, breezes will freshen overnight due to an approaching frontal boundary. High pressure will build across the Eastern Seaboard in its wake, slowly migrating into the western North Atlantic over the next several days. Hazardous marine conditions are expected to continue through at least Wednesday. As the high slowly weakens, breezes will begin to slacken by Thursday. Gentle to moderate breezes are expected for Friday and Saturday.

AVIATION

(00Z TAFS) Issued at 930 PM EDT Mon Apr 20 2026 A frontal boundary will push towards the Keys overnight, supporting winds clocking around to the northeast, along with frequent gusts 20 to 25 knots after 06z this evening. Showers with isolated thunder will be possible, although confidence in timing and coverage is too low to support anything beyond a window of VCSH for now. This will be reevaluated for the 06z overnight TAF issuance.

PRELIMINARY POINT TEMPS/POPS

Key West 72 81 72 81 / 30 30 0 10 Marathon 72 79 72 79 / 30 30 0 0

KEY WATCHES/WARNINGS/ADVISORIES

FL...None. GM...Small Craft Advisory until 6 AM EDT Wednesday for GMZ031>035- 042>044-052>055-072>075.