Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
240 FXUS62 KKEY 201834 AFDKEY Area Forecast Discussion National Weather Service Key West FL 234 PM EDT Thu Jun 20 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 230 PM EDT Thu Jun 20 2024 The Florida Keys remain entrenched in a complicated synoptic- scale pattern. In the upper-levels, CIMSS satellite-derived vorticity product highlights a closed low centered just to the southwest of the upper-levels. Meanwhile, in the lower troposphere, a tropical wave now centered over the northern Bahamas continues to propagate west northwestward towards northern Florida. Surface analysis reveals a weak low pressure system centered near the same location, Tropical Depression Alberto over eastern Mexico continuing to weaken, and a sprawling area of high pressure centered just north of Bermuda bifurcating these features. GOES-16 visible satellite imagery clearly highlights the broad cyclonic (counterclockwise) composite flow straddling the Florida Keys. Skies are partly to mostly cloudy across the Florida Keys and the adjacent nearshore and offshore coastal waters. Earlier scattered shower and thunderstorm activity has generally waned over the past several hours, as a wave of relatively dry air evident on water vapor imagery upstream of the Keys continues to filter westward. Temperatures are generally in the mid to upper 80s at the island communities. A challenging forecast will continue over the next several days, as the features described above interact. In addition, another Central American Gyre (CAG) cell is progged to develop over the Yucatan peninsula tomorrow, then slide northwestward into the Bay of Campeche early next week, pushing tropical moisture in our vicinity. All of these features will tend to elevate rain and thunder chances well above climatology. However, an examination of satellite- derived layer- averaged total precipitable water products suggest spokes of dry air from higher latitudes will occasionally propagate into the CWA. The first of this has begun, and visible satellite imagery shows mostly clear skies upstream in the vicinity of the Bahamas, including Andros Island. Given this, near-normal rain and thunder chances appears appropriate for tonight. Friday looks like a transition day, as more moist air progresses into our coastal waters from the east. Forecast soundings for late Friday through Sunday show deep, tropical moisture for this time frame, with the aforementioned upper-level trough lurking in the vicinity. Given this scenario, nearly every shower will have the chance to achieve thunderstorm status, and thus have elected to raise thunder chances to the elevated category for these forecast periods. The upper-level trough will gradually weaken as it slides southward out of our coastal waters on Sunday. This will be in tandem with the CAG cell dissipating. A climatologically- consistent area of high pressure will build over the North Atlantic. In this scenario, rain chances should return to near normal, driven by any tropical troughs and associated moisture undulations pushing into our area from the east southeast. Due to cloud cover, temperatures will be at or just below normal through the weekend, gradually rebounding to near normal for much of next week. && .MARINE... Issued at 230 PM EDT Thu Jun 20 2024 Small craft should continue to exercise caution for all Florida Keys coastal waters overnight except the Florida Bay, with easterly winds 15 to 20 knots. From synopsis, strong high pressure centered north of Bermuda working in tandem with Tropical Depression Alberto over eastern Mexico will result in moderate to fresh breezes through this evening. A second, weak area of low pressure currently near the northern Bahamas will continue to move west northwest, reaching the southeast U.S. by early Friday morning. The interaction of these features will loosen the pressure gradient, leading to slackening east to southeast breezes for Friday through the weekend. High pressure building over the North Atlantic early next week will result in light to gentle southeast to south breezes. && .AVIATION... (15Z TAFS) Issued at 230 PM EDT Thu Jun 20 2024 VFR conditions will prevail at both EYW and MTH through the TAF period. Shower activity will return early this evening so VCSH is included from 20z onward. Near surface winds are easterly at near 15 knots with gusts at times of up to 25 knots. && .CLIMATE... On this date in 1983, an F1 tornado produced $2.5m in damage near Lower Sugarloaf Key. There were no tropical cyclones in the area. && .PRELIMINARY POINT TEMPS/POPS... Key West 88 79 88 79 / 50 30 40 50 Marathon 88 80 88 80 / 40 30 40 50 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...None. GM...None. && $$ Public/Marine/Fire...BT Aviation/Nowcasts....AP 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