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| #1108711 (Received by flhurricane at: 10:56 AM 24.Sep.2022) TCDAT4 Tropical Storm Ian Discussion Number 6 NWS National Hurricane Center Miami FL AL092022 1100 AM EDT Sat Sep 24 2022 Ian still has an asymmetric appearance in satellite imagery this morning, with most of the deep convection located over the western portion of the circulation. Tail Doppler radar and dropsonde data from a NOAA Hurricane Hunter aircraft indicate the cyclone is still vertically tilted, with the low- to mid-level center displaced to the south of the surface center. This structure is likely a product of the northerly shear that has affected the cyclone since genesis. The aircraft reported 700-mb flight-level winds of 43 kt and SFMR retrievals slightly above 35 kt, which supports keeping the initial intensity at 40 kt for this advisory. The initial motion is a bit south of due west at 260/13 kt. A generally westward motion is expected through tonight as the cyclone is steered by a narrow ridge to its north. Ian is forecast to turn northwestward on Sunday and north-northwestward on Monday as it moves across the northwestern Caribbean Sea around the periphery of the ridge. The NHC track forecast during this period has been adjusted slightly south and west of the previous one, in line with the track consensus aids. Beyond 72 h, there is still a large amount of cross-track spread in the guidance as Ian emerges into the eastern Gulf of Mexico and approaches Florida. Hopefully, data collected from special radiosonde releases beginning later today and a scheduled NOAA G-IV flight will help resolve the steering flow around Ian and deep-layer trough that is forecast to be over the eastern U.S. early next week. The guidance envelope has once again shifted westward this cycle, and the official NHC track forecast has been adjusted in this direction as well, though it still lies slightly to the east of the TVCA and HCCA aids. Further adjustments to the track forecast may be needed given the increased uncertainty in the day 3-5 period. Ian is moving into a lower shear environment over very warm waters, and it should not take long for the system to shed its tilted structure and develop an inner core. Once that occurs, significant to rapid intensification is expected while Ian crosses the northwestern Caribbean Sea. The intensity guidance unanimously supports strengthening during the next several days, and the SHIPS-RII probabilities indicate a 67 percent chance of a 65-kt intensity increase in 72 h. Therefore, the NHC track forecast has been raised from the previous one, showing Ian becoming a hurricane by late Sunday and approaching western Cuba at or near major hurricane strength by Monday night. Limited land interaction is expected as the cyclone quickly passes over western Cuba, and Ian is forecast to be a major hurricane over the eastern Gulf of Mexico on Tuesday and Wednesday as it approaches the west coast of Florida. Key Messages: 1. Ian is expected to produce heavy rainfall, flash flooding, and possible mudslides in areas of higher terrain, particularly over Jamaica and Cuba. Limited flash and urban flooding is possible with rainfall across the Florida Keys and Florida peninsula through mid next week. 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. Ian is forecast to move near or over western Cuba and approach the west coast of the Florida peninsula at or near major hurricane strength early next week, where there is increasing confidence in multiple life-threatening hazards: storm surge, hurricane-force winds and rainfall flooding. While it is too soon to determine the exact magnitude and location of these hazards, residents in Cuba, the Florida Keys, and the Florida peninsula should ensure they have their hurricane plan in place, follow any advice given by local officials, and closely monitor updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 24/1500Z 14.4N 75.2W 40 KT 45 MPH 12H 25/0000Z 14.5N 76.8W 45 KT 50 MPH 24H 25/1200Z 15.5N 78.9W 55 KT 65 MPH 36H 26/0000Z 17.0N 80.7W 70 KT 80 MPH 48H 26/1200Z 18.8N 82.3W 85 KT 100 MPH 60H 27/0000Z 20.7N 83.4W 95 KT 110 MPH 72H 27/1200Z 22.7N 84.1W 100 KT 115 MPH 96H 28/1200Z 26.0N 83.9W 105 KT 120 MPH 120H 29/1200Z 28.6N 82.9W 95 KT 110 MPH $$ Forecaster Reinhart |
