Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
068 FXUS62 KKEY 210830 AFDKEY Area Forecast Discussion National Weather Service Key West FL 430 AM EDT Sat Sep 21 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 430 AM EDT Sat Sep 21 2024 Very quiet conditions, especially for September, prevail across the Florida Keys on this early Saturday morning. Radars detect only isolated showers over the distant Straits of Florida. Temperatures along the island chain are mostly in the lower 80s, but have radiated down to the mid 70s at the typical cooler spot of North Big Pine thanks to clear skies, calm winds, and slightly lower dewpoints in the mid 70s. Surface analysis depicts a nearly non-existent gradient across the area, with a weak trough over the western Atlantic extending westward through the Bahamas and into the Straits, and weak high pressure over the Eastern Seaboard. Aloft, the Keys lie just west of the base of a lengthy trough axis which extends northeastward across the western Atlantic. The 00Z Key West sounding sampled near average PW for the date at 1.71 inches, but more recent GOES-TPW satellite imagery shows that a drier airmass, with estimated PWs between 1.5 and 1.6 inches, has filtered southward into our area overnight, as the trough axis aloft eases just to our east. Generally quiet weather with below normal rain chances will prevail across the Keys today and through the weekend, with extensive dry air in the mid to upper levels likely to suppress convection. There may be just enough low level moisture along with light albeit somewhat chaotic flow in the lower to mid levels to allow for some island cloud line development today, and have retained 25-30 percent PoPs. An even drier airmass is forecast for tonight and Sunday, and reduced PoPs to 20 percent for those periods. Otherwise, expect light breezes to continue, with highs around 90 and lows mostly in the lower 80s. Heading into next week, forecast uncertainty increases greatly, as eyes turn to our southwest, where a late September Central American Gyre (CAG) is forecast to develop over the SW Caribbean or near the Yucatan Peninsula. The CAG will likely aid eventual development of a tropical surface low development in that region, although timing and subsequent movement of any such low remain highly uncertain at this time. We do have gradually increasing confidence that the Keys will see freshening E/SE breezes starting on Tuesday, as our local gradient tightens between building high pressure along the Eastern Seaboard and expected lower pressure near the CAG. Have continued to advertise increasing rain and thunder chances as we head into the middle of next week, and have also introduced breezy wording beginning on Wednesday. We continue to emphasize that the extended forecast will likely change during the next several days as the eventual evolution of any tropical low resulting from the CAG becomes more clear. Residents and visitors in the Keys are encouraged to check back for the latest forecast updates through the weekend and into next week. && .MARINE... Issued at 430 AM EDT Sat Sep 21 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, as above normal tides continue. Boaters can expect less clearance under fixed bridges, especially during the hours around high tide. Late night observations show mostly NE to E breezes of 5 knots or less along the reef and at Long Key C-MAN, with seas at Satan Shoal running below a half foot. From the synopsis, as a trough slides slowly eastward across the western North Atlantic through the weekend and into early next week, high pressure building along the Eastern Seaboard will bring gradually increasing easterly breezes to the Keys coastal waters beginning on Monday. Heading into the middle of next week, the forecast will depend on the potential development and movement of low pressure over the northwestern Caribbean Sea. At this time, we expect freshening east to southeast breezes, with the strongest winds over western sections of the Keys waters. && .AVIATION... (06Z TAFS) Issued at 430 AM EDT Sat Sep 21 2024 VFR conditions will prevail at EYW and MTH through Saturday evening. Near surface winds will gradually trend from variable to easterly throughout the day. Occasional showers will be able to form across the Keys and brief MVFR CIGs cannot be ruled out. && .CLIMATE... On this day in 1948, a hurricane intensified as it moved north northeast from Cuba, crossing Boca Chica Key as Category 3 storm. At Boca Chica the peak wind was 122 mph before the anemometer blew away, with an estimated peak wind of 140 mph. In Key West the minimum pressure was measured at 28.45 inches, with a daily- record 4.53 inches of rain. && .KEY WATCHES/WARNINGS/ADVISORIES... FL...Coastal Flood Advisory for FLZ076. GM...None. && $$ Public/Marine/Fire...Jacobson Aviation/Nowcasts....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