Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
383 FXUS62 KKEY 210230 AFDKEY Area Forecast Discussion National Weather Service Key West FL 1030 PM EDT Fri Sep 20 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 1030 PM EDT Fri Sep 20 2024 Earlier convection that was around during the late afternoon hours south of the Middle Keys and across the offshore Gulf waters near the Dry Tortugas dissipated fairly quickly by 4-5 pm. KBYX radar remained very quiet for the next few hours until around 830 pm. Looking at GOES 16 Nighttime Microphysics imagery you can see the remnant outflow boundaries from earlier convection across the mainland moving south to southwest through Florida Bay and the Upper Keys. Due to mesoscale processes as well as boundary collisions, scattered showers and thunderstorms formed rapidly between 830 to 9 pm. This activity slowly progressed to the south near 5 knots resulting in a few Special Marine Warnings as well as Marine Weather Statements. One of the storms was able to reach up to 50 to 55 kft indicative of very robust updrafts. This activity was waning though with most of the activity having diminished by 1030 pm. Outside of this, it has remained quiet for much of the Keys. Temperatures along the Island Chain are in the lower to mid 80s. However, Big Pine has cooled to a nice 77 degrees this evening due to the clear sky and light winds due to radiational cooling as the nights have been getting longer. Marine platforms around the Keys are observing variable winds near 5 knots with Island Chain communities observing variable winds less than 5 mph. .SHORT TERM FORECAST... The 12z sounding displayed a fairly moist lower level atmosphere with quite a bit of drying above 700 mb. In addition, CAPE values are quite high around 2500 J/kg and a PWAT value of 1.72 inches which is right around the median for the date. The only source for potential convection overnight seems to be the aforementioned outflow boundary continuing its journey southwestward along the Island Chain. Though, there are also things working against this, GOES 16 TPW products shows a tongue of 1.40 to 1.75 inch PWAT moving over much of the Keys. So while we have the potential trigger and instability, now we are lacking the moisture. Therefore, have opted to drop PoPs down to 20% for overnight due to this. && .MARINE... Issued at 1030 PM EDT Fri Sep 20 2024 There are currently no watches, warnings, or advisories in effect across the Florida Keys coastal waters. From synopsis, as a trough slides slowly eastward into the western North Atlantic this weekend, 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. .COASTAL FLOOD... 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. && .AVIATION... (00Z TAFS) Issued at 1030 PM EDT Fri Sep 20 2024 VFR conditions are expected to prevail at EYW and MTH terminals through the overnight and into the morning hours on Saturday. Latest radar imagery shows showers and thunderstorms have been waxing and waning along a boundary that has moved off the South Florida mainland. This is expected to continue slowly progressing southwestward along the Island Chain reaching MTH between 21/03-06z and then EYW between 21/06z-10z. However, due to uncertainty as to if a shower or thunderstorm will form, opted to leave VCSH and VCTS out of the TAFs for now. Near surface winds are expected to be mostly light and variable into the overnight hours becoming more northeast to east towards the morning hours. && .PRELIMINARY POINT TEMPS/POPS... Key West 90 82 90 82 / 40 40 30 30 Marathon 90 81 91 81 / 40 40 30 30 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...Coastal Flood Advisory until 5 PM EDT Saturday for FLZ076. GM...None. && $$ Public/Marine/Fire...MJV Aviation/Nowcasts....MJV Data Acquisition.....DR Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest