textproduct: Key West

KEY MESSAGES

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

- Heavy rainfall is becoming increasingly likely. Most locations in the Keys can generally expect an additional 2 to 4 inches of rainfall through Sunday, with locally higher amounts possible.

- Gentle to moderate (10 to 15 mph) breezes will relax by Friday. While breezes will then be light to gentle (5 to 10 mph) through the weekend, gusty winds will be possible with any thunderstorm.

AVIATION

(18Z TAFS) Issued at 140 PM EDT Thu Sep 17 2026 Scattered showers and thunderstorms will remain in the vicinity of the terminals throughout the TAF period. The greatest coverage in sub-VFR ceilings and visbilities will be through 00z this evening, with a low confidence in wind direction for gusts associated with any thunderstorm outflow. Coverage is expected to wane in the evening hours, before redevelopment may occur in the late overnight and Friday morning hours. Have included just a mention of VCSH in that extended period for now due to lack of confidence in the extended TAF forecast evolution.

PREV DISCUSSION

Issued at 308 AM EDT Thu Sep 17 2026 Models are in good agreement that the center of the upper low will move across central Florida later this week and into the start of the weekend, promoting broad cyclonic flow aloft. As to be expected with the proximity of this feature, this will keep rain chances elevated over the coming days. At the same time the upper low continues to make its approach towards central FL, the surface flow locally across the Keys lessens to generally less than 10 knots, which could favor a messy scenario where daily convective activity could be driven by boundary collisions and make for slow-moving erratic storm motions at times. The core of the colder air aloft with temps as low as -8C to -9C looks to stay just north of our area closer to the center of the upper low but 500 mb temps are still projected to lower to around -7C and this should help to steepen mid-level lapse rates at times. Thus, the end result of this pattern with persistent forcing for ascent in the form of the upper low, cooling mid level temperatures, and PWATs in excess of 2 inches, an unsettled stretch of weather is expected with daily PoPs in the high chance to likely range. By late weekend and early next week, the upper low shifts into the east-central Gulf but models differ with when this feature ultimately departs as the ECMWF opens this feature into a trough and lifts out of the region by Monday but the GFS lingers the closed circulation into Tuesday. Regardless, its influence across the region will lessen by early next week but PoPS may remain elevated well through the end of the long term period as attention might start to turn to the south of the Keys by the middle of next week. Several ensemble members on a variety of global models show deep tropical moisture from the Caribbean potentially streaming into the area, which could be related to the Central American Gyre and this would make sense from a climatological perspective as this feature tends to become more established in the early fall time frame. While there remains considerable uncertainty in exact forecast details at this time, trends will need to be monitored closely in the subsequent forecast issuances as the synoptic picture becomes more clear.

MARINE

Issued at 945 AM EDT Thu Sep 17 2026 Scattered showers and thunderstorms will grow in coverage and intensity through the afternoon and evening hours. Any stronger thunderstorm will be capable of producing gusty winds, as well as suddenly building and confused seas.

From synopsis, high pressure across the North Atlantic will maintain gentle to moderate northeast to east breezes through tonight. Winds will then slacken for Friday through the start of the weekend, becoming light to gentle out of the east and southeast, as the high north of the Keys marine zones weakens. An increasingly wet pattern will develop across the Florida Keys coastal waters through at least Sunday, as an upper- level low retrogrades westward towards South Florida and then eventually the Gulf. Confidence is low in the marine forecast for early next week, largely determined by where the upper-level low resides for that time frame.

KEY WATCHES/WARNINGS/ADVISORIES

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