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| #1108809 (Received by flhurricane at: 10:56 PM 24.Sep.2022) TCDAT4 Tropical Storm Ian Discussion Number 8 NWS National Hurricane Center Miami FL AL092022 1100 PM EDT Sat Sep 24 2022 A NOAA G-IV Hurricane Hunter jet flew a surveillance around and across Ian at high altitude earlier this evening and dropped several dropsondes near the estimated center. The surface winds from the instruments suggested that Ian had an elongated surface circulation from northwest to southeast, but one dropsonde in particular had a lower pressure than the others, which helped to located the center. Some new convection has been forming near this location recently, which provides a little more confidence in the estimate. The minimum pressure has fallen to 1002 mb, a consensus of satellite intensity estimates suggests that the maximum winds are now near 45 kt. The track forecast reasoning remains unchanged, with Ian expected to curve around the western periphery of the Atlantic subtropical ridge through the 5-day forecast period. There has also been little change in the individual model solutions--the ECMWF remains on the eastern side of the guidance envelope and the GFS remains on the western side. Since there has been no significant change in the guidance, the new NHC track forecast is very similar to the previous one through day 3, although it has been nudged slightly westward (again) on days 4 and 5 over the eastern Gulf of Mexico in the direction of the TVCN and HCCA consensus aids. Ian is now in an environment of low shear and high atmospheric moisture and over waters of high ocean heat content. Once the circulation becomes vertically stacked, which should be soon, these conditions favor rapid intensification (RI) while Ian moves over the northwestern Caribbean Sea. Several RI indices support this scenario, with the Deterministic to Probabilistic Statistical Rapid Intensification Index (DTOPS) in particular showing a greater than 90 percent chance of RI during the ensuing 48- and 72-hour forecast periods. The NHC official forecast explicitly shows RI beginning on Sunday, with Ian predicted to peak at category 4 intensity over the eastern Gulf of Mexico in about 3 days. By days 4 and 5, global models are leaning toward a scenario where Ian enters into an environment of very strong southwesterly shear, and weakening is therefore expected while Ian approaches the coast of the Florida panhandle. That said, Ian is likely to have an expanding wind field and will be slowing down by that time, which will have the potential to produce significant wind and storm surge impacts despite any potential weakening. Users are urged to not focus on specific forecast intensities in the 4- and 5-day forecasts and instead focus on the potential hazards Ian may produce across portions 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. Flash and urban flooding is possible with rainfall across the Florida Keys and Florida peninsula through mid next week. Additional flooding on rivers across northern Florida and parts of the Southeast cannot be ruled out. 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. Hurricane and tropical storm watches are now in effect for much of western Cuba. 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 long-term track and intensity forecast is higher than usual. Regardless of Ian’s exact track and intensity, 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 25/0300Z 14.7N 77.7W 45 KT 50 MPH 12H 25/1200Z 15.3N 79.3W 55 KT 65 MPH 24H 26/0000Z 16.6N 81.0W 70 KT 80 MPH 36H 26/1200Z 18.3N 82.5W 85 KT 100 MPH 48H 27/0000Z 20.1N 83.7W 100 KT 115 MPH 60H 27/1200Z 22.0N 84.5W 115 KT 130 MPH...OVER WEST TIP OF CUBA 72H 28/0000Z 23.9N 84.9W 120 KT 140 MPH...OVER WATER 96H 29/0000Z 27.2N 84.8W 115 KT 130 MPH 120H 30/0000Z 29.6N 84.1W 80 KT 90 MPH $$ Forecaster Berg |
