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| #1108620 (Received by flhurricane at: 10:47 PM 23.Sep.2022) TCDAT4 Tropical Storm Ian Discussion Number 4 NWS National Hurricane Center Miami FL AL092022 1100 PM EDT Fri Sep 23 2022 The system remains sheared from the northeast, with the low-level circulation evident a bit to the east of the deep convection. Unfortunately, we didn't have the benefit of a reconnaissance aircraft this evening to sample the winds, but satellite estimates did increase a bit. TAFB and SAB provided Dvorak classifications of T2.0/30 kt and T3.0/45 kt, respectively, while the objective UW-CIMSS ADT and SATCON estimates are at tropical storm intensity. Based on a blend of these data, the depression is upgraded to Tropical Storm Ian with 35-kt winds. Ian's center appears to have been moving more slowly this evening, and the initial motion estimate is west-northwestward, or 285/10 kt. The track guidance is in good agreement that Ian should turn westward during the next 12-24 hours while located to the south of a small mid-level anticyclone centered just north of Hispaniola. After 24 hours, Ian is expected to begin recurving around the western side of this high, turning northwestward over the northwestern Caribbean Sea, and then northward while crossing Cuba into the Gulf of Mexico and toward Florida. The track models agree on this general scenario, and the guidance envelope is flanked by the major global models, with the ECMWF taking a route over South Florida and the GFS farther west, remaining over the eastern Gulf of Mexico by day 5. The new NHC forecast lies between these two scenarios and is not much different from the previous forecast. The GFS and ECMWF ensembles both show a similar amount of spread as the deterministic guidance, but both ensemble means are close to the multi-model consensus aids, which helps to give more credence to the position of the official forecast. The moderate deep-layer shear affecting Ian is forecast to decrease during the next 6 to 12 hours, and the cyclone will be moving over the very warm waters of the central and northwestern Caribbean Sea, where sea surface temperatures are between 29 and 31 degrees Celsius. Intensification is expected to be gradual during the next 36 hours while Ian gets better organized in a lower-shear environment, but after that time, conditions will be conducive for faster strengthening. In fact, the NHC intensity forecast explicitly calls for rapid intensification (RI) between days 2 and 3 while Ian is moving over the northwestern Caribbean Sea toward western Cuba. It's worth nothing too that the RI indices from SHIPS are showing a 2-in-3 chance of a 65-kt increase in winds during the next 3 days, and if that transpires, Ian could be stronger than what's shown in the official forecast. The storm is not expected to be over Cuba long enough to cause much weakening, and the forecast still shows Ian as a major hurricane over the eastern Gulf of Mexico while approaching the west coast of Florida. Key Messages: 1. Ian is expected to produce heavy rainfall and instances of flash flooding and possible mudslides in areas of higher terrain, particularly over Jamaica and Cuba. 2. Hurricane conditions are possible in the Cayman Islands by early Monday, with tropical storm conditions possible by late Sunday. Tropical storm conditions are possible in Jamaica on Sunday. 3. Early next week, Ian is forecast to move near or over western Cuba as a strengthening hurricane and then approach the Florida peninsula at or near major hurricane strength, with the potential for significant impacts from storm surge, hurricane-force winds, and heavy rainfall. While it is too soon to determine the exact magnitude and location of these impacts, residents in Cuba, the Florida Keys, and the Florida peninsula should ensure they have their hurricane plan in place and closely monitor forecast updates through the weekend. FORECAST POSITIONS AND MAX WINDS INIT 24/0300Z 14.8N 72.0W 35 KT 40 MPH 12H 24/1200Z 14.7N 73.9W 40 KT 45 MPH 24H 25/0000Z 15.1N 76.3W 45 KT 50 MPH 36H 25/1200Z 16.1N 78.4W 50 KT 60 MPH 48H 26/0000Z 17.6N 80.1W 60 KT 70 MPH 60H 26/1200Z 19.3N 81.5W 75 KT 85 MPH...NEAR GRAND CAYMAN 72H 27/0000Z 21.2N 82.4W 90 KT 105 MPH 96H 28/0000Z 24.9N 83.0W 100 KT 115 MPH 120H 29/0000Z 28.0N 82.0W 95 KT 110 MPH...OVER FLORIDA $$ Forecaster Berg |
