Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
147 FXUS62 KKEY 200800 AFDKEY Area Forecast Discussion National Weather Service Key West FL 400 AM EDT Fri Sep 20 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 400 AM EDT Fri Sep 20 2024 Synoptic upper air analysis highlights a relatively amplified pattern for the eastern half of the CONUS. A now positively tilted trough stretches from western Cuba northeastward to just off the New England coastline. Meanwhile, a strong upper-level ridge continues to amplify upstream of this trough, with the dome stretching all the way from Mexico northward to the Great Lakes region. The surface reflection of these features is resulting in chaotic steering flow for the Florida Keys, coupled with anomalously low geopotential heights above the 500 mb isobaric surface sampled by last evening`s 00z sounding at KEY. At this early Friday morning, local available Doppler radars are detecting scattered showers and isolated thunderstorms dotting the Florida Keys island chain and the adjacent nearshore and offshore coastal waters. Given the aforementioned light steering flow and only modest synoptic forcing for ascent from the trough`s decaying influence, all convective activity continues to be driven by occasional mesoscale boundary collisions, mainly in the vicinity of the Lower Keys. Most island communities outside of the Lower Keys have remained dry overnight, with temperatures generally bottoming out near 80F. Today will likely be a transition day for the Florida Keys. Ample moisture depicted in today`s forecast soundings coupled with modest troughiness should promote further scattered showers and isolated thunderstorm development. Should there be a window of decent clearing with minimal disruptive boundary collisions, island cumulus cloud line formation will certainly be possible as well today. After today, continental dry air associated with the eastern flank of the ridge building across the Southeast will promote reduced rain and thunder chances for tonight through the weekend. Spread in global deterministic and ensemble numerical weather prediction guidance continues to be quite high for next week. There is quite a bit of model support that a Central American Gyre (CAG), a common feature this time of year, will form in the vicinity of the Yucatan Peninsula. Meanwhile, high pressure will further build across the Southeast. The CAG will likely support surface cyclogenesis somewhere in the western Caribbean, although exact timing and location of this cyclogenesis is quite uncertain at this time. Regardless of ultimate evolution of this expected area of low pressure, the interaction of this feature with the aforementioned high over the Southeast will likely support at least moderate to fresh easterlies by the middle part of next week. Beyond that, the ultimate track and strength of this low will dictate rain and thunder chances for the Keys. For now, it seems prudent to advertise at least near normal PoPs for the extended period, while emphasizing this extended forecast will likely undergo changes over the next several forecast iterations. Residents and visitors of the Keys are encouraged to check back for the latest forecast updates. && .MARINE... Issued at 400 AM EDT Fri Sep 20 2024 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, especially during the hours around high tide. Light and often variable breezes will continue today due to a persistent trough near the Atlantic Coast and a weak area of high pressure east of the Bahamas. The trough will slowly slide eastward into the western North Atlantic this weekend, as a ridge expands its control across the Southeast United States. Winds will begin to take on a predominantly light, easterly direction. Confidence in the extended marine forecast remains quite low and will be highly dependent on the expected formation of a low pressure system in the northwestern Caribbean Sea. Regardless of the ultimate fate of this low, breezes are expected to freshen by Tuesday, as the low interacts with high pressure over the Southeast. && .AVIATION... (06Z TAFS) Issued at 400 AM EDT Fri Sep 20 2024 VFR conditions prevail at EYW and MTH for the 20 Sept 06Z TAF period. Showers and thunderstorm activity will redevelop today around the terminals, but hi-res guidance is unclear about the timing. Near surface winds will slowly prevail out of the north tonight. Brief periods of MVFR or IFR CIGs are possible in showers and thunderstorms. && .CLIMATE... On this day in 2018, the daily record high temperature of 95F was recorded in Key West. This temperature is also tied for the warmest temperature recorded in September. Temperature records for Key West date back to 1872. Also of note, in 2005, Hurricane Rita passed 45 miles south of Key West as a Category Two hurricane. Key West recorded sustained winds of 62 mph and gusts to 76 mph. Marathon reported sustained winds of 41 mph and gusts to 52 mph. Flooding 2 feet above ground level flooded up to 4 blocks inland in midtown Key West. Up to 200 residences affected by storm surge in Key West. Storm tides estimated at 3 to 5 feet above mean sea level. Numerous coastal streets flooded with U.S. Highway One flooded at Sea Oats Beach on Lower Matecumbe Key. Rainfall totaled 4.26 inches at John Pennekamp State Park in Key Largo. && .PRELIMINARY POINT TEMPS/POPS... Key West 90 82 90 81 / 40 30 30 30 Marathon 90 81 90 81 / 40 30 30 30 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...Coastal Flood Advisory until 5 PM EDT this afternoon for FLZ076. GM...None. && $$ Public/Marine/Fire...BT Aviation/Nowcasts....AJP Data Acquisition.....AJP Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest