Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
739 FXUS62 KKEY 151843 AFDKEY Area Forecast Discussion National Weather Service Key West FL 243 PM EDT Sun Sep 15 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 1235 PM EDT Sun Sep 15 2024 Bizarre September weather patterns continue across the Florida Keys. A general lack of synoptic forcing remains across the southern CWA. While thunderstorms are able to fire over the Outer Gulf Waters along a boundary between GOES- derived drier air, estimating 1 inch PWAT, and the deep tropical air of near 2 inches measured by the morning 12Z sounding, the line of showers is unlikely to reach the Florida Keys. Outflow boundaries from this convection are possible, and disorganized pop up showers may develop along these boundaries. Heat index values at EYW exceeded 108F as of 1040 EDT, so hot and muggy conditions continue through 7 PM tonight. After weeks of light and variable winds with hot, muggy days across the islands, the atmosphere is beginning to develop new synoptic features. A trough over the southeastern coast of the United States, designated as Invest AL95 by the National Hurricane Center, will move onshore in the Carolinas during the first half of the week. Deep layer troughing will be amplified over Florida and this feature is expected to develop into a cutoff low by midweek. There are several implications for Florida Keys weather. First, the trough will direct very deep layers of moisture across the Keys with some guidance suggesting PWAT values as high as 2.5 inches. Second, winds may transition from light and variable to persistent southeasterlies, providing a source of near-surface lift over the CWA. Third, if the trough moves south and west enough, then a weak right entrance region of an upper level jet could further enhance vertical motion and support development of deep thunderstorms. Thus PoPs for Tuesday and Wednesday were increased to 50%. A surge of moisture mid-week will not bring the trough`s influence to an end. Ensemble model guidance shows the cut off low retrograding and deepening further late in the week, and the Keys are very close to its associated trough axis. Statistical model QPF spread is thus all over the place. The spread in statistical ensemble guidance for 24 hour QPF on Sunday is nearly an inch of rainfall. All this to say that confidence in the forecast for this weekend is low beyond a general statement of "wet and cloudy." At the very least, the heat advisories are coming to an end. && .MARINE... Issued at 1235 PM EDT Sun Sep 15 2024 A Coastal Flood Statement remains in effect for the Florida Keys. Ponding on the typically favored roadways will peak at the times of the morning higher high tide in the Lower and Middle Keys, with little tidal cycle relief in the Upper Keys. Other than these minor coastal flooding hazards, are no watches, warnings, or advisories in effect for the Florida Keys coastal waters. From synopsis, light and frequently variable breezes will continue through Friday over the Florida Keys coastal waters. A developing low pressure system off the Carolina coast will generate a higher swell off the Upper Keys for Tuesday and Wednesday. The low will deepen into an upper level trough and slowly slide south towards the Florida Peninsula by Friday. Unpredictability in the movement of this trough means confidence in the extended forecast is very low. && .AVIATION... (15Z TAFS) Issued at 1235 PM EDT Sun Sep 15 2024 While VFR conditions will prevail across the terminals for the TAF period, moist low-levels coupled with light southwesterly flow will support an existing cloud line to grow over the next several hours. In addition, residual boundaries from South Florida Mainland storms may shoot southward, promoting additional vicinity showers. Have elected to include a window of VCSH in the TAFs for now, which will be amended as needed to include impacts to visbilities and ceilings. && .CLIMATE... On this day in Keys weather history, in 2023, the daily record high temperature of 94F was last recorded at Key West International Airport and Marathon International Airport. Temperatures records for Key West and Marathon date back to 1872 and 1950 respectively. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...Heat Advisory until 7 PM EDT this evening for FLZ076>078. GM...None. && $$ Public/Marine/Fire...AJP Aviation/Nowcasts....BT Data Acquisition.....BT Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest