Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
983 FXUS62 KKEY 180917 AFDKEY Area Forecast Discussion National Weather Service Key West FL 517 AM EDT Wed Sep 18 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 517 AM EDT Wed Sep 18 2024 Its another early start for convective activity around the Florida Keys this morning. Boundaries drifting west over the island chain and Straits of Florida have come alive with convection over the last couple of hours. Storm coverage spans the waters south of the Dry Tortugas and the Lower and Middle Keys as well as over the Middle Keys with new cells bubbling along both old and new outflow boundaries alike. Clearly the overworked atmosphere from yesterday evening`s sounding has recovered as these showers gradually develop northwest towards the rest of the island chain. Outside of storm activity, temperatures across the Keys are in the lower to mid 80s with seemingly unphased dewpoints in the upper 70s. Light to gentle east to southeasterly breezes are observed along the Reef as a weak surface high from the Atlantic steers storms to the west northwest. Our short term forecast is very similar to yesterday`s. Numerous showers and scattered thunderstorms are expected to percolate across our area today and perhaps into tonight. Conditions for convective development prevail from Tuesday with a very moist (PW values >2 inches) and decently unstable (model sounding estimates ML CAPE value ~1500) atmosphere. The deep layer trough centered over southeast CONUS is still aloft in our area with nearly zonal westerly breezes above 850 mb. While this is somewhat of a discontinuity with our surface flow, the speed shear it provides will aid in storm ventilation. We also have the same hindrances to convective development as yesterday as well. Weak surface flow will be unable to provide any organized large scale lift meaning that initiation will depend almost exclusively on mesoscale factors. This is not an issue at the moment but boundaries could fizzle out during a lull in precipitation due to overwork and delay the next round to early the next morning (similar to yesterday). Opted to keep likely PoPs today and nudged up to high end chance PoPs for tonight and tomorrow as the upper level features seem to linger around a bit longer than originally thought. The troughing in the southeast will lift across the Eastern Seaboard by this weekend, returning us to near normal PoPs for this time of year. Weak surface flow will also prevail meaning eyes will be on both cloud lines generated near the island chain and boundaries ejected from mainland Florida and Cuba to spark showers in the Keys waters. This status quo is expected to hold throughout the weekend. Guidance starts to diverge towards the middle of next week as the GFS pulls for a developing tropical wave in the western Caribbean and the ECMWF does not. Stay tuned to the National Hurricane Center and your friendly local Florida Keys weather office in the coming days for a more refined solution. && .MARINE... Issued at 517 AM EDT Wed Sep 18 2024 From synopsis, light and generally variable breezes will continue through the remainder of the week. Expect higher winds and seas in and around thunderstorms. Northerly swell generated by a low near the Eastern Seaboard will linger through Wednesday. This disturbance will meander southeast to southward this weekend and into early next week and deepen as it interacts with an upper level trough. Unpredictability in the movement of this trough means confidence in the extended forecast is very low. A Coastal Flood Advisory remains in effect for the Upper Keys, and a Coastal Flood Statement remains in effect for the Middle and Lower Keys. Boaters can expect less clearance under fixed bridges. && .AVIATION... (06Z TAFS) Issued at 517 AM EDT Wed Sep 18 2024 Showers and thunderstorms will be the prevailing weather feature throughout the morning and afternoon. For now, will continue to keep VCSH in TAFs, and will include timing of RA or TS if and when the timing becomes clearer. This also means that intermittent periods of MVFR, or lower, conditions are possible from any one strong shower or thunderstorm moving over either terminal. With the low confidence related to timing of deteriorating conditions, short-term updates and amendments will likely be needed. && .CLIMATE... On this day in 1926, "the Great Miami Hurricane" made landfall in Miami at category 4 intensity, bringing Hurricane force winds to the Upper Keys. In Key West, the minimum pressure was 29.48" and the maximum sustained wind was 52 mph. && .PRELIMINARY POINT TEMPS/POPS... Key West 90 81 90 80 / 60 50 50 50 Marathon 90 81 90 81 / 60 50 50 50 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...Coastal Flood Advisory until 5 PM EDT this afternoon for FLZ076. GM...None. && $$ Public/Marine/Fire...JAM Aviation/Nowcasts....DP Data Acquisition.....DP Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest