Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
129 FXUS62 KKEY 201941 AFDKEY Area Forecast Discussion National Weather Service Key West FL 341 PM EDT Mon May 20 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 241 PM EDT Mon May 20 2024 Water vapor imagery highlights a mid to upper-level low exiting the Atlantic Bight. Mean-layer ridging is well to our west, placing the Keys in the dry and sinking western flank of the upper trough axis. Nevertheless, isolated thunderstorms continue to capitalize on the steep mid-level lapse rates. The thunderstorm behavior has changed though. From early this morning through the early afternoon, lines of storms aligned with the mean layer shear propagated both up and down shear, leading to astronomical rainfall totals. Radar derived and gauge totals suggest maxima near 5" in Lower Matecumbe, close to 10" across portions of western Vaca Key, and 5 to 7" for areas between Big Coppitt to Sugarloaf. Everybody got more than an inch except areas east of Key Largo. It is remarkable how quickly things can change given nearly three rain-free weeks. Marathon has not measured rain since April 30th and just set its all time monthly rainfall record (7.08" as of 300 PM). .FORECAST... The upper-level trough will sharpen tonight through Wednesday with the axis dipping south across central Cuba. More or less at the same time, a mid-level vort lobe noted on water vapor imagery nearing the FL/GA line will pivot into the eastern Gulf and round into the base of the upper-level trough. Typically the back side of these anticyclonic wave breaks are dry and stable. This may not be the case through the short term. Low-level steering will remain weakly confluent and variable at times. Forecast soundings suggest lower tropospheric moisture will be adequate through 700 mb to support rain and thunder chances, and sort of an ideal scenario for a mesoscale feast of outflows and triggers. We advertise 30% chances through the short term, well above the MOS consensus. There will be a short window Wednesday night through Thursday night when drier air invades the profile before the easterlies resume. We advertise near-normal (20%) rain chances through the extended with meager low-level moisture and a rather non-descript pattern of undulation in the easterlies. Good news in the heat department, the oppressive heat/humidity of the last week will not make a return over the next week. && .MARINE... Issued at 241 PM EDT Mon May 20 2024 Thunderstorms will decrease in coverage as breezes veer to the northwest and increase. Tuesday through Wednesday, breezes will gradually shift to the east as high pressure in the western North Atlantic builds back in across the region. Gentle east to southeast breezes will resume Friday through Saturday. && .AVIATION... (18Z TAFS) Issued at 241 PM EDT Mon May 20 2024 Earlier convection that moved through both terminals has finally waned with KBYX radar showing any thunderstorm activity now well off to the south and west. With the atmosphere largely worked over for the time being, we expect the next few to several hours to largely remain quiet outside of a brief isolated shower. Therefore, expect VFR conditions to continue through the remainder of the afternoon and into the evening hours. Hi-res guidance is showing another potential round of convection overnight into Tuesday morning. However, this will largely depend on how much the atmosphere is able to destabilize after being worked over today. Due to the uncertainty, have opted to leave mention of VCSH or VCTS out of TAF for now. Winds will continue to be influenced bu the convective environment for at least the next few hours before becoming westerly to northwesterly tonight. && .CLIMATE... So far today, Marathon has recorded 7.08 inches as of the 253 pm observation. The previous record for the date was 1.68 inches set back in 1991. Rainfall records for MTH date back to 1950. && .PRELIMINARY POINT TEMPS/POPS... Key West 79 89 79 89 / 30 30 30 20 Marathon 80 89 80 89 / 30 30 30 30 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...None. && $$ Public/Marine/Fire...CLR Aviation/Nowcasts....MJV 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