textproduct: Key West

KEY MESSAGES

- Moisture will linger across the region through the weekend, supporting near to above normal rain and thunderstorm chances.

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

- Heat index values will range from 100-108 degrees daily with little relief from the muggy conditions overnight. Know the signs of heat stress, take frequent breaks, and stay hydrated.

DISCUSSION

Issued at 1017 PM EDT Sat Sep 12 2026 The evening started a bit quiet across the Florida Keys. However, in the late afternoon a cloud line formed north of the Lower Keys. Waterspouts were confirmed north of Cudjoe, and the atmosphere did not let up for the entire night. A combination of outflow boundaries from Cuba, the cloud line over the Lower Keys, and showers off South Florida led to swaths of vigorous convection across the entire CWA. Winds in this environment were relatively light, meaning the showers that formed were nearly stationary. Considering the 00Z KKEY sounding sampled an environmental PWAT of 2.34 inches, the showers that were able to form generated a significant amount of rainfall. Radar derived estimates placed nearly 2 inches of rain over parts of the Lower Keys and Key Largo near the 18 mile stretch. If you were in the Florida Keys tonight, you were treated displays of lightning akin to the Great Plains.

What exactly happened this evening? To start, there were no features in the upper atmosphere that were preventing heavy showers. A check of advected layer PWAT indicated that no layer of the atmosphere from the surface to 300 mb was abnormally dry. Wind speeds through the lower 20,000 feet of the atmosphere were comparatively light. The average speed from the surface to 10,000 feet measured by the KKEY sounding was 2 knots. However, a check of satellite-derived winds hints at what happened. A slight bit of positive vorticity was present just east of the Florida Keys. Environmental streamlines hinted at a weak trough in the lower levels of the atmosphere. That in combination with the deep layers of moisture and the buildup of instability from a comparative lack of convection primed the environment for thunderstorms. All that was necessary was a source of lift, provided by the previously mentioned cloud line, the Cuban landmass, and South Florida.

Overnight, expect the environment to have stabilized after the rounds of showers and thunderstorms. Even though occasional thunderstorms will be able to form over the Keys waters, the kind of thunderstorm observed over the waters is less likely. Winds are on track to weaken down light and variable. Muggy conditions will be able to rapidly return. Brace for another round of showers across the Keys tomorrow. For now, at least, weather patterns hint that the overnight hours will be comparatively calmer.

MARINE

Issued at 1017 PM EDT Sat Sep 12 2026 No watches, warnings, or advisories are in effect for the nearshore or offshore waters of the Florida Keys.

From synopsis: Ridging across the southeastern United States and Florida will maintain light to gentle east to southeasterly breezes over the next few days, becoming variable at times. Low level moisture will remain abundant and keep convective potential near to above through the weekend, but fall back to near normal early in the week as drier lower levels filter in. The ridge will be reinforced late in the forecast and may drive freshening northeast to easterly breezes.

AVIATION

(00Z TAFS) Issued at 1017 PM EDT Sat Sep 12 2026 VFR conditions will prevail for the rest of the TAF period. Near surface winds are likely to remain light, somewhat variable, unless showers are able to redevelop. Overnight hours are expected to have less shower development near the island terminals, but it cannot be discounted. After sunset, VCSH becomes more likely with VCTS possible.

PRELIMINARY POINT TEMPS/POPS

Key West 82 92 81 92 / 30 40 30 40 Marathon 82 90 82 90 / 30 40 30 30

KEY WATCHES/WARNINGS/ADVISORIES

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