Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
778 FXUS62 KKEY 050232 AFDKEY Area Forecast Discussion National Weather Service Key West FL 1032 PM EDT Thu Sep 4 2025 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 1000 PM EDT Thu Sep 4 2025 Today was one of the rare days where the Florida Keys were socked in with cloud cover and one and off shower activity all day. Total rainfall amounts reported from available gauge data ranged from around 1-4" in the Lower Keys, 0.5-1.5" in the Middle Keys, and between 0.25-0.5" in the Upper Keys. Similar to the past several days, convection waned in the early evening hours, leaving the entire Island Chain currently dry and under partly cloudy skies. The 00z evening sounding at KEY revealed a surprising stable, dry layer from the surface up to around 700 mb, consistent with substantial inhibition and minimal mixed layer instability. We hypothesize that this is derived from locally-induced dry adiabatic subsidence from the copious amount of convection today, rather than induced by synoptic advection of upstream dry air. Given the local source of the subsidence, and the fact that the frontal boundary to our north has made little movement, we expect restoration and charging to occur of the low-levels overnight, with another round of scattered to widespread convection emerging by the late overnight hours in the vicinity of the Keys. In addition, most numerical weather prediction guidance suggests south to southwesterlies clocking around to the southwest to west from west to east around sunrise, which will support confluence and additional forcing for ascent. Given this reasoning, have elected to retain the likely PoPs for the overnight hours. Outside of minor adjustments to wind speeds and directions early in the overnight period, no changes made to the inherited forecast. && .MARINE... Issued at 1000 PM EDT Thu Sep 4 2025 Similar to the past several nights, shower and thunderstorm activity is under a lull currently across the Keys marine zones. However, additional activity is expected to develop by late tonight. Any stronger storm will produce locally gusty winds, cloud to surface lightning strikes, and confused seas. From synopsis, a broad surface low along a stationary front stretching from the Gulf eastward to the Florida Peninsula will maintain southwesterly winds across the Florida Keys marine zones. The front will remain rooted in place through the next few days, while the low meanders northeast into the western North Atlantic, promoting southwest to west breezes. Abundant moisture will promote well above normal rain and thunder chances through the end of the work week. High pressure slowly building across the North Atlantic over the weekend will support reduced rain and thunder chances, although remaining at or above normal. && .AVIATION... (00Z TAFS) Issued at 1000 PM EDT Thu Sep 4 2025 A convective lull currently in the vicinity of the island terminals is expected to continue through at least 06z, before additional showers and storms are expected to form and push to EYW and MTH thereafter, likely lasting through much of the rest of the 00z TAF period. Have elected to just reintroduce a general period of VCSH after 06z at EYW an 09z at MTH, with specific impacts to visibilities and ceilings to be handled by later TAF amendments. This will be reevaluated at the 06z TAF forecast cycle. && .PRELIMINARY POINT TEMPS/POPS... Key West 79 91 80 91 / 60 80 50 50 Marathon 79 89 80 89 / 60 80 50 50 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...None. && $$ Public/Marine/Fire...BT Aviation/Nowcasts....BT Data Acquisition.....MJV Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest