Area Forecast Discussion
Issued by NWS Key West, FL
Issued by NWS Key West, FL
419 FXUS62 KKEY 241733 AFDKEY Area Forecast Discussion National Weather Service Key West FL 133 PM EDT Tue Sep 24 2024 ...New DISCUSSION, MARINE, AVIATION... .DISCUSSION... Issued at 133 PM EDT Tue Sep 24 2024 KBYX radar shows mainly isolated showers moving to the west to northwest near 15 knots with one lonely thunderstorm right at the edge of the westernmost distant Straits of Florida. GOES 16 Visible satellite imagery shows mainly cumulus and stratocumulus across the Keys, however, the high cirrostratus from now Tropical Storm Helene can be seen streaming over the Keys. The more dense cirrus overcast remains over Cuba and northwestern Caribbean Sea for the time being. Temperatures along the Island Chain are in the mid to upper 80s with some locations such as Big Pine Key in the lower 90s. Dew points remain quite humid in the mid to upper 70s which is making the heat indices reach between 100 to 105 degrees. Weak high pressure remains in place across the Eastern Seaboard along with now Tropical Storm Helene in the northwestern Caribbean Sea per the National Hurricane Center. The two of these working in tandem are creating for a tightening pressure gradient across the Keys resulting in marine platforms observing east to southeast breezes near 15 knots. Island Chain communities are observing near 15 mph with occasional gusts to near 20 mph. .FORECAST... In the upper levels, ridging remains in place across the Keys for the time being with this expected to start weakening as we head towards the evening and overnight hours. However, between 850 to 700 mb, moisture has been increasing and is expected to continue to do so over the next several hours leading to continued increasing cloud cover and higher rain chances than previous days with 40% maintained for the afternoon with 50% for the Lower Keys. Also, the aforementioned pressure gradient is expected to only gradually strengthen, therefore, we expect breezes to only slowly increase heading through the remainder of the afternoon and into the evening hours. Moisture continues to further increase across the Keys tonight as Tropical Storm Helene in the northwestern Caribbean Sea continues moving northwestward towards the Yucatan Channel while further strengthening. Therefore, maintained the 70% chance PoPs for tonight. Also, breezes will continue to increase as Tropical Storm Helene continues to strengthen in combination with the weak high pressure off the north. Both of these will work in tandem to create a tightening pressure gradient even outside from where the core of Helene tracks. Wednesday through Thursday is when we expect the wettest and windiest weather throughout the Keys as Helene makes its closest approach to the Keys Wednesday night. The Lower Keys and the Dry Tortugas are now under a Tropical Storm Warning with Middle Keys under a Tropical Storm Watch. While the forecast track of the system is expected to remain well west of the Keys, there will be an expansive wind field with it resulting in far reaching impacts. Therefore, it is important not to focus on the exact path of the system as the effects will be far-removed from the center. For the latest info on Tropical Storm Helene, please visit the National Hurricane Centers website for the latest track and advisory information. Also, the Weather Prediction has the Keys in a marginal risk for excessive rainfall from Wednesday through Friday. The Keys can expect thundery squalls over this time frame with strong gusty winds embedded within the squalls. Thursday night through Friday night, as the system continues moving rapidly northward due to increased forward speed making landfall as a hurricane in the Big Bend area of Florida, we expect the "tail" of the system to remain over the Keys prolonging the wet period for a little bit longer. Over the weekend and into early next week, upper level ridging as well as drier air moves back into the Keys returning us to the typical early autumn pattern as we approach the start of October. Temperatures will remain on the warm side though near 90 degrees by day and lower 80s overnight. && .MARINE... Issued at 133 PM EDT Tue Sep 24 2024 Tropical Storm Warnings are in effect for the following zones: both offshore Gulf waters zones and the westernmost Straits of Florida from the Seven Mile Bridge west as well as the nearshore waters surrounding the Lower Keys. Tropical Storm Watches are in effect for the nearshore waters surrounding the Middle Keys and the Straits of Florida off the Middle Keys. For the easternmost zones, Small Craft Should Exercise Caution for Increasing winds remain in effect for the rest of the afternoon with Small Craft Advisory Conditions expected Wednesday headlined. From synopsis, moderate to fresh east to southeasterly breezes will continue to slowly increase through the afternoon. This will be in response to a high pressure building along the Eastern Seaboard, and Tropical Storm Helene in the northwestern Caribbean Sea. Tropical Storm Helene is expected to continue moving slowly northwestward through Wednesday morning before turning more north and then north northeastward while accelerating Wednesday afternoon through Thursday. The closest pass from Helene to the Florida Keys coastal waters is expected to be Wednesday evening through Thursday morning when the peak southeasterly wind and highest seas is expected to occur. As the storm passes, breezes will shift to the south to southwest while gradually diminishing with seas gradually subsiding Thursday night through Friday. Winds further diminish heading through the weekend. .COASTAL FLOOD... A Coastal Flood Statement remains in effect for all of the Keys island chain, as above normal tides continue. Boaters can expect less clearance under fixed bridges, especially during the hours around high tide. A Coastal Flood Watch is remains in effect for all the Florida Keys from Wednesday evening through Thursday afternoon. Please see the watch for more details. && .AVIATION... (15Z TAFS) Issued at 133 PM EDT Tue Sep 24 2024 Squalls will begin to increase in coverage over the next 24 hours as Tropical Storm Helene starts to trek north. Ahead of the main event (likely Wednesday evening through Thursday afternoon), occasional squalls will pass over the terminals tonight which will likely require TEMPOs. Surface winds will slowly increase overnight, with southeasterly gusts of 20 to 25 knots expected at MTH and gusts near 25 knots at EYW by early tomorrow morning. Winds will only continue to increase thereafter. Conditions will deteriorate by tomorrow afternoon, with fast-moving squalls capable of gusts near 45 knots and MVFR to IFR conditions likely. && .PRELIMINARY POINT TEMPS/POPS... Key West 81 85 81 86 / 70 90 90 80 Marathon 81 87 81 87 / 70 80 90 80 && .KEY WATCHES/WARNINGS/ADVISORIES... FL...Coastal Flood Watch from Wednesday evening through Thursday afternoon for FLZ076>078. Tropical Storm Watch for FLZ077. Tropical Storm Warning for FLZ078. GM...Tropical Storm Watch for GMZ032-043-053-073. Tropical Storm Warning for GMZ033>035-044-054-055-074-075. && $$ Public/Marine/Fire...MJV Aviation/Nowcasts....NB Data Acquisition.....AP Visit us on the web at weather.gov/key Follow us on Facebook and Twitter at: www.facebook.com/nwskeywest www.twitter.com/nwskeywest