Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
482 FXUS62 KKEY 260112 AFDKEY Area Forecast Discussion National Weather Service Key West FL 912 PM EDT Fri Jul 25 2025 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 910 PM EDT Fri Jul 25 2025 Data from the Key West evening radiosonde balloon indicated a classic elevated Saharan Air Layer overhead, with a nearly adiabatic temperature lapse rate between 5000-10000 feet elevation, and a deep layer of dry air aloft. Not surprisingly, Key West Doppler Radar base reflectivity scans indicate rain-free conditions across the service area. In fact, both satellite and surface observations reveal only isolated, shallow, fair-weather cumulus clouds across the Florida Keys, much of the southern Florida Peninsula, Straits of Florida, and the Bahamas. Satellite-derived total precipitable water values are well-below climatological values across this same area, with our balloon data indicating 1.20 inches. Despite an otherwise very unstable thermodynamic stratification, it will be nearly impossible for any significant cumulus convection to arise overnight owing to the deleterious effects of dry air entrainment upon incipient young cumulus updrafts. The large-scale pattern features a nearly stationary deep layer mean anticyclone centered over the Atlantic off the Carolinas, with ridging and anticyclonic flow along its southern flank, and across the Florida Keys and adjacent coastal waters. The associated surface high pressure cell was centered just north of the Bahamas, with a decent gradient flow between the high center and lower pressures over the western Caribbean. Subsequently, and as expected, fresh ESE breezes prevail across most of the Keys and adjacent coastal waters, with the highest wind speeds over the Straits of Florida. A satellite altimeter pass earlier today indicated significant wave heights of 4-6 feet in the Straits of Florida between the Cay Sal Bank and the upper Keys, and this is consistent with a prevailing ESE wind of 15-20 knots. Current air temperatures in Keys island communities are in the mid 80s, with dewpoint temperatures in the mid to upper 70s yielding heat indices in the mid to upper 90s. Easterly winds are blowing steady at 15-20 mph under mostly clear skies, which provides some (but little) relief to the late-July heat and humidity. For overnight and Saturday, we can expect a rare rain- and lightning-free forecast, as the extremely dry air aloft of Saharan origin inhibits development of showers and thunderstorms. Breezes likely are near their peak, and should begin to decrease early Saturday, and further on Sunday. && .MARINE... Issued at 910 PM EDT Fri Jul 25 2025 No watches, warnings, or advisories are in effect for Florida Keys coastal waters. However, Small Craft Should Exercise Caution all zones overnight. A high pressure cell centered over the western North Atlantic east of the Florida Peninsula will maintain moderate to fresh east to southeasterly breezes across Florida Keys coastal waters overnight. The high pressure cell will weaken slowly from Saturday through Monday, resulting in diminishing breezes through early next week. A dry and stable air mass associated with a Saharan Air Layer aloft will eliminate or significantly limit shower and thunderstorm activity from tonight through Saturday night. A somewhat weaker pressure pattern will promote mostly light to gentle breezes through the middle of next week. && .AVIATION... (00Z TAFS) Issued at 910 PM EDT Fri Jul 25 2025 Through 26/24Z, prevailing VFR conditions are expected at both EYW and MTH, with steady easterly winds and only a few shallow passing cumulus clouds. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...None. && $$ Public/Marine/Fire...Kasper Aviation/Nowcasts....Kasper 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