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| #1058999 (Received by flhurricane at: 5:02 AM 28.Aug.2021) TCDAT4 Hurricane Ida Discussion Number 8 NWS National Hurricane Center Miami FL AL092021 400 AM CDT Sat Aug 28 2021 Just after the last advisory, the convective structure of Ida got a bit ragged, probably due to the residual effects of land interaction with Cuba and a tongue of dry air that wrapped into the eastern side of the circulation. However, latest radar images from Cuba show that the eye is becoming better defined, and satellite imagery shows cooling of the cloud tops in the eyewall. The initial intensity has been held at 70 kt based on the latest trends and earlier Hurricane Hunter aircraft data. NOAA and Air Force reserve Hurricane Hunter aircraft are scheduled to investigate Ida again starting around 12Z. The initial motion remains northwestward or 315/14. A subtropical ridge centered off the southeast U.S. coast is expected to shift westward through the weekend, and this feature should continue to provide a steering flow that will take Ida steadily northwestward across the Gulf of Mexico during the next 36-48 h. The track guidance remains in good agreement that Ida will make landfall on the coast of southeastern or central Louisiana late Sunday or early Monday morning. After landfall, Ida is expected to turn northward through Louisiana and western Mississippi at a slower forward speed as it moves around the western end of the ridge. Recurvature into the westerlies and an east-northeastward motion are expected by the end of the forecast period. The new forecast track is nudged slightly to the west after 36 h to keep it near the various consensus models, but this is not a significant change from the previous forecast. Users are again reminded to not focus on the exact details of the track forecast as storm surge, wind, and rainfall impacts will extend far from the center. Ida is expected to remain in a favorable environment of light vertical shear and very warm sea-surface temperatures until it makes landfall. The only negative factor is the possibility that dry air may try to entrain into the system and slow the expected intensification. The SHIPS and LGEM models are showing a little less strengthening than previously. However, the HWRF and HMON models continue to forecast Ida to reach Category 4 intensity before landfall. The new intensity forecast will forecast a peak intensity of 120 kt in best agreement with the HWRF and HMON, and the pre-landfall part of the forecast is little changed from the previous forecast. After landfall, rapid weakening is expected due to land interaction, drier air, and an increase in shear, and Ida is expected to become a post-tropical cyclone as it moves through the Tennessee Valley. As Ida continues to intensify over the Gulf of Mexico, an expansion of its wind field is predicted. The NHC wind radii forecast is largely based on the radii consensus, and winds of at least tropical storm force are likely to reach the coast Sunday morning. Therefore, all preparations to protect life and property for this dangerous event need to be made today. Key Messages: 1. Hurricane and tropical storm conditions are ending over Cuba. However, Ida will continue to bring periods of heavy rain across western Cuba through today that may lead to flash flooding and mudslides. 2. There is a danger of life-threatening storm surge inundation Sunday along the coasts of Louisiana and Mississippi within the Storm Surge Warning area. Extremely life-threatening inundation of 10 to 15 feet above ground level is possible within the area from Morgan City, Louisiana, to the Mouth of the Mississippi River. Interests throughout the warning area should follow any advice given by local officials. 3. Ida is expected to be an extremely dangerous major hurricane when it reaches the coast of Louisiana. Hurricane-force winds are expected Sunday in portions of the Hurricane Warning area along the Louisiana coast, including metropolitan New Orleans, with potentially catastrophic wind damage possible where the core of Ida moves onshore. Actions to protect life and property should be rushed to completion in the warning area. 4. Ida is likely to produce heavy rainfall later Sunday into Monday across the central Gulf Coast from southeast Louisiana to coastal Mississippi resulting in significant flash and riverine flooding impacts. As Ida moves inland, flooding impacts are possible across portions of the Lower Mississippi and Tennessee Valleys. FORECAST POSITIONS AND MAX WINDS INIT 28/0900Z 24.0N 85.2W 70 KT 80 MPH 12H 28/1800Z 25.4N 86.9W 85 KT 100 MPH 24H 29/0600Z 27.1N 88.9W 105 KT 120 MPH 36H 29/1800Z 28.6N 90.5W 120 KT 140 MPH 48H 30/0600Z 30.1N 91.3W 85 KT 100 MPH...INLAND 60H 30/1800Z 31.6N 91.2W 45 KT 50 MPH...INLAND 72H 31/0600Z 33.2N 90.5W 30 KT 35 MPH...INLAND 96H 01/0600Z 36.0N 87.0W 25 KT 30 MPH...INLAND 120H 02/0600Z 37.5N 82.5W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Beven |
