textproduct: Key West

KEY MESSAGES

- A moisture surge will support scattered rain and thunderstorm chances from Labor Day into midweek.

- The primary threat for any stronger thunderstorms will be dangerous lightning strikes. When thunder roars, go indoors. If on a boat, stay low, or go below.

- Heat index values will range from 100-105 degrees daily, with little relief in the muggy conditions overnight. Know the signs of heat stress, take frequent breaks, and stay hydrated.

DISCUSSION

Issued at 954 PM EDT Sun Sep 6 2026

The Florida Keys remains on the far southern periphery of a positively tilted longwave trough with axis centered over the Eastern Seaboard extending southwest into the northeastern Gulf. An associated surface front is in the process of stalling nearly east to west along the Gulf Coast region. Plentiful amounts of tropospheric moisture remain in place south of the front across Florida and the adjacent Gulf and Atlantic waters. This combining with weak but sufficient cyclonic flow will continue to promote chances for showers and thunderstorms across the Keys and our surrounding waters. Although in a slight lull this evening, which has been the case for the past few days, we should see a resurgence in convection shortly after sunrise. The main thing to watch over the next several hours will be activity developing along a cuban outflow which is clearly evident on KBYX radar moving northward in the Straits of Florida. And as usual, mesoscale boundaries will continue to be primary initiators of convection through the day tomorrow. In addition, expect light to variable winds by the afternoon which may promote the development of another broken cloud line and associated thunderstorms near the Lower Keys. All this to say, no changes have been proposed to the forecast at this time. Outside of a cooling shower/storm, temperatures along the island chain will warm into the lower 90s with dewpoints in the upper 70s. For those enjoying outdoor Labor Day festivities, afternoon heat index values are forecast to range between 100-105 degrees, and extra heat safety precautions should be taken.

MARINE

Issued at 954 PM EDT Sun Sep 6 2026

An outflow boundary moving northward from Cuba is generating isolated thunderstorms in the Straits of Florida. This boundary may continue to generate activity over the next few hours as it moves towards the nearshore waters of the Lower to Middle Keys. Mariners encountering this activity may experience locally hazardous winds and seas.

From synopsis, light to gentle southeast breezes will prevail through mid week, as weak steering flow persists across the region. Thereafter, breezes will freshen to gentle to moderate, as high pressure builds in. Waves of low-level moisture pushing across the Keys will support elevated rain and thunder chances through Tuesday, possibly returning to near normal by mid week.

AVIATION

(00Z TAFS) Issued at 725 PM EDT Sun Sep 6 2026

VFR conditions have returned to both terminals with a lull in convection near the Keys this evening. Light and VRB winds will become southerly during the overnight and early morning hours. Ample amounts of low-level moisture remain in place across the area, and thunderstorm redevelopment is forecast to occur around sunrise. A PROB30 for TSRA was introduced at both sites from 10-14Z. Additional activity may impact flight conditions late in this TAF period, but forecast confidence is too low to mention impacts beyond 14Z in this issuance.

KEY WATCHES/WARNINGS/ADVISORIES

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