Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
793 FXUS62 KKEY 180138 AFDKEY Area Forecast Discussion National Weather Service Key West FL 938 PM EDT Sat Aug 17 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 935 PM EDT Sat Aug 17 2024 An upper-level composite analysis this evening indicates that the Florida Keys are in a very nondescript synoptic-scale environment, with the nearest deep layer mean anticyclone centered over the Texas Panhandle, Hurricane Ernesto over 1000 miles ENE of the Florida Keys, and the trade-wind belt centered well south of the area, in the central/southern Caribbean basin. As a result, very light winds prevail throughout the depth of the troposphere, as shown by data from the Key West evening radiosonde balloon. In fact, the balloon measured wind speeds below 10 knots through nearly the entire depth of the atmosphere below 30,000 feet elevation. Not surprisingly, radar cell motions have been very slow. Despite the lack of synoptic-scale forcing, it is August, and the moist static energy in the atmospheric boundary layer is significant, resulting in more-than-adequate potential buoyancy for deep cumulus convection and a conditionally very unstable thermodynamic profile (MLCAPE >2000 J/kg). In addition, convective inhibition energy was very weak. For much of today, scattered to numerous (albeit slow-moving) showers and some thunderstorms traversed portions of the Florida Keys and adjacent coastal waters, bringing heavy downpours and locally gusty winds. However, recent Doppler radar trends have shown a decrease in both coverage and intensity of cells across the service area. At present, Doppler radar data show numerous old outflow boundaries lurking (in addition to the distinct base reflectivity patterns of early- season southward-migrating birds). Despite the current low precipitation coverage, I am reluctant to tamper with the first-period forecasts (showing 40%/scattered showers/thunderstorms) given both the observed thermodynamic environment and presence of numerous old outflow boundaries and potential lifting mechanisms for subsequent convective cells overnight. We probably will adjust low temperatures slightly. Although air temperatures near 80F will be likely where it rains and in island interior locations (radiative "cooling"), air temperatures probably will remain in the lower-mid 80s within about 1 km of the water. && .MARINE... Issued at 935 PM EDT Sat Aug 17 2024 No watches, warnings, or advisories are in effect for Florida Keys coastal waters zones. Observed prevailing breezes have ranged from E 10-15 knots over the eastern zones to variable near 5 knots over the western zones. The Sand Key C-MAN station has been averaging E 5-10 knots over the last several hours, with the nearby Satan Shoal buoy measuring significant wave heights of 1-2 feet. Wave heights likely are a foot or two higher in the eastern marine zones. We appreciate the diligence of the crew of the NOAA Ship NANCY FOSTER, who have been reporting hourly from out near Dry Tortugas National Park. Winds should become more uniform across the area overnight as they turn out of the southeast and south as the regional pressure pattern changes slightly. && .AVIATION... (00Z TAFS) Issued at 935 PM EDT Sat Aug 17 2024 Through 18/24Z, prevailing VFR conditions are expected at both EYW and MTH. Transient, sub-VFR episodes certainly are possible at both terminals given the environment and potential for showers or thunderstorms. However, the 1- to 6-hour probabilities are as yet too low for forecast confidence and inclusion in the TAFs. We will issue timely amendments when satellite/radar/lightning data offer higher forecast confidence. && .CLIMATE... On this day in 1886, a tropical storm intensified into a hurricane as it moved west-northwestward across the Straits of Florida, about 50 miles south of Key West, where a minimum sea level pressure of 1005 mb, or 29.68 inches of mercury, was recorded, along with a peak wind of 48 mph and numerous gusts to 60 mph. A man was killed when a building collapsed on Duval Street. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...None. && $$ Public/Marine/Fire...Kasper Aviation/Nowcasts....Kasper Data Acquisition.....11 Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest