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| #1108766 (Received by flhurricane at: 4:59 PM 24.Sep.2022) TCDAT4 Tropical Storm Ian Discussion Number 7 NWS National Hurricane Center Miami FL AL092022 500 PM EDT Sat Sep 24 2022 The satellite presentation of Ian has improved this afternoon. The associated deep convection shows increased signs of organization, and the deep-layer shear appears to have diminished over the cyclone based on more extensive upper-level outflow noted in visible satellite imagery. An Air Force Hurricane Hunter aircraft found 850-mb peak flight level winds of 44 kt and several SFMR retrievals greater than 40 kt, while dropsonde data suggest the minimum pressure has not changed much since the previous flight. A blend of these data support an initial intensity of 40 kt for this advisory. The aircraft data suggest the center could be re-forming slightly west of previous estimates, so the initial motion is an uncertain 265/14 kt. Ian is expected to move westward through early Sunday before turning northwestward around the southwestern periphery of a ridge to the north. A north-northwestward to northward motion is forecast on Monday and Tuesday as the center of Ian passes near or over the western tip of Cuba and emerges over the southeastern Gulf of Mexico. Overall, the westward trend in the track models continues, with the latest GFS on the far left side of the guidance envelope and the ECMWF on the right edge. The track forecast is still highly uncertain at days 4-5, with the GFS and ECMWF positions about 200 n mi apart by 96 h. There is significant spread noted even among the GFS ensemble members, with positions that range from the north-central Gulf of Mexico to the west coast of Florida. Hopefully, data collected from special radiosonde releases and a NOAA G-IV flight this evening will help better resolve the steering flow around Ian and the deep-layer trough that is forecast to be over the eastern U.S. early next week. The latest NHC track forecast is once again adjusted westward, and further adjustments may be needed given the increased uncertainty in the day 3-5 period. Ian is expected to significantly strengthen over the next few days as it moves within a low shear environment over SSTs greater than 30 deg C in the northwestern Caribbean Sea. As the structure of the cyclone continues to improve and Ian develops an inner core, rapid intensification (RI) appears very likely. The SHIPS-RII probabilities continue to highlight this potential, with a 66 percent chance of a 65-kt intensity increase in 72 h. The NHC intensity forecast has been raised substantially through 96 h, and it now shows Ian reaching major hurricane strength by late Monday before it nears western Cuba. These changes closely follow the IVCN and HCCA consensus aids, although there remains guidance even higher than the current forecast. Ian is forecast to remain a major hurricane as it moves northward across the eastern Gulf of Mexico and approaches Florida. Environmental conditions could become less favorable late in the period due to southerly shear associated with the aforementioned trough, but Ian is expected to remain a large and powerful hurricane through the period. 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 or tropical storm conditions are expected on Grand Cayman beginning early Monday. 3. Ian is forecast to be a major hurricane when it passes near or over western Cuba, and there is increasing confidence in a life-threatening storm surge and hurricane-force winds in portions of western Cuba beginning late Monday. 4. Ian is expected to remain a major hurricane when it moves generally northward across the eastern Gulf of Mexico during the middle of next week, but uncertainty in the track forecast is higher than usual. Regardless of Ian’s exact track, there is a risk of dangerous storm surge, hurricane-force winds, and heavy rainfall along the west coast of Florida and the Florida Panhandle by the middle of next week, and residents in Florida 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 24/2100Z 14.3N 77.0W 40 KT 45 MPH 12H 25/0600Z 14.6N 78.4W 50 KT 60 MPH 24H 25/1800Z 15.7N 80.3W 60 KT 70 MPH 36H 26/0600Z 17.4N 82.2W 75 KT 85 MPH 48H 26/1800Z 19.2N 83.5W 95 KT 110 MPH 60H 27/0600Z 20.9N 84.4W 110 KT 125 MPH 72H 27/1800Z 23.1N 85.0W 115 KT 130 MPH 96H 28/1800Z 26.2N 84.8W 115 KT 130 MPH 120H 29/1800Z 28.7N 83.9W 90 KT 105 MPH $$ Forecaster Reinhart |
