textproduct: Key West

KEY MESSAGES

- Well above normal rain chances (around 60-70%) will persist across the Florida Keys through the rest of the weekend and into early next week.

- Heavy rainfall is expected at times. There is a marginal risk for excessive rainfall through Monday morning.

- While breezes will be light to gentle (5 to 10 mph) throughout the weekend, gusty winds and locally hazardous seas are expected in the vicinity of thunderstorms.

DISCUSSION

Issued at 951 PM EDT Sat Sep 19 2026

It has been an eerily benign evening across the FLorida Keys this evening as we have waited in anticipation for more activity on radar. It is worth mentioning that there was one shower that was able to hug the Bayside shore of Marathon at sunset, and it was able to produce a couple of waterspouts, so it hasn't been entirely quiet. We has previously advertised more active conditions to occur this evening, but the forecast has fallen short so far. With the very weak steering flow in the lower levels, approximately 2 mph of flow, we have needed outflow boundaries from the mainland to push off of the southern tip of the peninsula to serve as our lift to initiate convection. The most recent scans from our KBYX radar show that this anticipated boundary is currently across the southeastern Gulf and Bayside waters, and is slowly progressing toward the island chain. The delay in this boundary has helped to delay our expected wet weather. Another contributing factor to this was widely spread cirrus debris from convection outside of our forecast area from this morning and afternoon. A clear sky helps to efficiently destabilize our environment, but a broken cirrus shield similar to what we saw earlier can slow down some of the destabilization. Our 00Z KKEY sounding from this evening calculated approximately 846 J/kg of CAPE, which is still enough to support active weather, but there was also some inhibition noted in the same profile. All of this is to say that, at face value, the current forecast is not up to par. However, we are going to maintain the elevated rain and thunder chances overnight. The northern portion of the outflow boundary is currently interacting with some isolated thunderstorms over the southeastern Gulf waters, and has supported/maintained the activity over the past hour or so. There are a few showers to the south of the Lower Keys, and if the boundary can catch up to them, then it's possible that there will be another lightning show to our south overnight. There is also a rogue ghost boundary in between Key West and the Tortugas, and if the mainland boundary can catch up to this specific boundary, we expect that to trigger activity. CAMs guidance also continue to favor overnight activity, supporting confidence to some degree.

Cautiously, there are no changes to the forecast package with this nighttime update.

MARINE

Issued at 951 PM EDT Sat Sep 19 2026

Light and variable breezes overnight will gradually become east to southeasterly by sunrise with the initially isolated shower and thunderstorm activity increasing by morning. This on and off pattern of activity will continue through the rest of the weekend, and virtually any of these showers and thunderstorms will be able to produce locally hazardous marine conditions including gusty and erratic strong winds, confused seas, and blinding downpours.

AVIATION

(00Z TAFS) Issued at 951 PM EDT Sat Sep 19 2026 Some low level cloud debris traversing the area may cause intermittent MVFR CIGs at either island terminal throughout the TAF period, especially near sunrise. Initial light and variable surface winds will gradually become east to southeasterly and crosswind concerns are low due to both magnitude and direction of the wind. However, an increase in showers and thunderstorms is anticipated during the TAF period, so we are opting to maintain a mention of VCSH.

PRELIMINARY POINT TEMPS/POPS

Key West 78 90 79 90 / 60 60 60 60 Marathon 79 88 80 88 / 60 60 60 60

KEY WATCHES/WARNINGS/ADVISORIES

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