textproduct: Key West

KEY MESSAGES

- Well above normal rain chances (around 60-70%) will persist across the Florida Keys through the remainder 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 351 AM EDT Sun Sep 20 2026 GOES-19 satellite imagery shows broad cyclonic flow across the entire state of Florida as an upper level low continues to remain stalled in the eastern Gulf waters off the SWFL coast. This feature has failed to make much westward progress as ridging aloft near the Ark-La-Tex region remains in place so this disturbance will continue to linger in the eastern Gulf waters for the remainder of the weekend and into the start of the new week. Despite the close proximity of this feature, the core of cold air aloft has remained to the north of our area so far this weekend and the 20/00Z KEY RAOB sampled a 500 mb temperature of -5.7 C, which was considerably warmer than the sounding from Saturday morning which had a value of -8.3 C, near the 10th percentile for this time of the year. Thus, this warming trend aloft has likely played a significant role in why convective development has been more suppressed than what the official forecast and model guidance had suggested so far this weekend. That said, will continue to maintain elevated rain chances for the remainder of the weekend as the upper level low to the north continues to still favor increased forcing for ascent across the region with divergence aloft and an increase in vorticity advection. Since this feature remains in an environment of weak steering, it may be able to drift just far enough southward today to possibly allow mid level temps to cool a touch further once again and bring a slightly more favorable thermodynamic environment today with better mid-level lapse rates compared to what was observed yesterday. Additionally, the low level flow will become more southerly today so this should bring a slight uptick in moisture quality with PWATs in excess of 2 inches area-wide, though the southerly flow will also of course be more susceptible to Cuban shadow influence. Regardless, there should be enough ingredients in place to support scattered to occasional numerous showers and thunderstorms across the Florida Keys and surrounding coastal waters today, which could also be enhanced further if a cloud line is able to take advantage of a light/VRB wind flow developing in the late afternoon hours. While the cloud line scenario remains to be seen, activity should have no issues developing late evening and overnight as there should be plenty of mesoscale boundaries during the overnight hours to provide additional initiation sources.

The upper level low is forecast to open into a trough late Monday and into Tuesday as it becomes absorbed in a mid-latitude trough into mid week. Lingering moisture in the wake of this feature should still support elevated rain chances on Monday with PoPs peaking from 50% to 70%. As the weakening upper low lifts off of Northeast FL on Tuesday, it will aid it in the development of coastal low off in Southwest Atlantic with this system expected to lift to the north-northeast through mid to late week, deepening as it does so. As this occurs, a frontal boundary associated with this system will drop southward across the central Florida peninsula mid week and potentially push through south Florida by the end of the week. Whether or not this frontal boundary can push all the way through south Florida and the Keys remains in question at the moment, but a deepening upper level trough across the eastern CONUS may provide enough push to allow the boundary to sweep through. If this frontal passage occurs, the air mass change in the wake of the boundary this early in the season may fall short of bringing a significant noticeable change in temperatures with a decrease in dewpoints and humidity values being the more likely outcome. In addition to this frontal boundary, there will also be a surge of tropical moisture being funneled northward from the Caribbean potentially associated with an inverted trough feature that may move across the Yucatan Channel. While amplifying ridging across east Texas in the middle of the week and the aforementioned frontal boundary pushing southward across the peninsula would suggest that most of the moisture associated with this increase in tropical moisture should get directed to the west of the Florida Keys, there should be enough increase in moisture to keep rain chances elevated through the middle of the week before moisture levels decrease towards the end of the week as the frontal boundary drags a drier air mass into the region.

MARINE

Issued at 351 AM EDT Sun Sep 20 2026 Light to gentle mainly southerly breezes will be in place through the remainder of the weekend, though a period of variable winds are expected during the late afternoon and evening hours on Sunday. In addition, a wet weather pattern will continue to persist across the Florida Keys coastal waters into the new week as an upper-level low lingers in the eastern Gulf waters. As a result, scattered to numerous showers and thunderstorms will be a daily occurence with gusty winds, lightning strikes, blinding downpours, and locally hazardous seas being the main hazards mariners could encounter in the vicinity of this activity. The upper-level low is forecast to move out of the area by Tuesday, but lingering moisture is likely to persist through at least the middle of the week so rain chances will continue to remain elevated. Winds will generally remain light to gentle into the new week but brief periods of moderate winds may occur in the evening hours with winds remaining mostly out of the south to southeast.

AVIATION

(06Z TAFS) Issued at 351 AM EDT Sun Sep 20 2026 Scattered SHRA/TSRA may occur as times throughout the period a slow moving disturbance lingers to the north of the Florida Keys. If any of this activity directly impacts either of the Island Chain terminals, brief flight restrictions of MVFR/IFR will be possible, especially during periods of heavier precipitation. Outside of any the shower and thunderstorm activity, VFR conditions will prevail with mostly light southerly winds around 5 kts today, potentially becoming light/VRB briefly this evening before increasing to 5-10 knots overnight out of the south.

KEY WATCHES/WARNINGS/ADVISORIES

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