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| #1059100 (Received by flhurricane at: 4:53 PM 28.Aug.2021) TCDAT4 Hurricane Ida Discussion Number 10 NWS National Hurricane Center Miami FL AL092021 400 PM CDT Sat Aug 28 2021 Ida's satellite presentation has continued to improve this afternoon, with the eye becoming more apparent in both infrared and visible satellite imagery. The eye is surrounded by a symmetric ring of cold cloud tops and new convection with lightning as seen by the GOES-16 GLM sensor has been rotating around the western portion of the eyewall within the past few hours. The upper-level outflow has also become well established over the hurricane and several spiral bands are noted over the northern semicircle. Subjective Dvorak satellite intensity estimates have increased to T5.0 and these support increasing the initial intensity to 90 kt for this advisory. Both NOAA and Air Force Reserve reconnaissance aircraft are scheduled to be in the hurricane within the next few hours and should provide additional information on Ida's current strength. Earlier aircraft and satellite wind data indicate that the tropical-storm-force wind field has continued to expand over the eastern semicircle and the initial wind radii have been adjusted outward. The hurricane appears to have begun its anticipated rapid intensification phase. A favorable upper-level wind pattern, warm waters along the track, and a moist atmosphere are expected to allow for additional rapid strengthening overnight and early Sunday. This is again supported by the majority of the intensity models, and the NHC wind speed forecast continues to call for rapid strengthening, bringing Ida to Category 4 status within 12 to 18 hours. An eyewall replacement cycle could occur as Ida nears the northern Gulf coast, so some fluctuations in intensity are possible during that time. After landfall, rapid weakening is expected, and Ida is forecast to become a post-tropical cyclone by day 4, and it is likely to be absorbed along a frontal zone by day 5. Ida has moved a little to the right of the previous track, but the long-term motion motion is still northwestward or 320/14 kt. The track forecast philosophy remains unchanged. Ida is expected to continue on a northwestward heading through late Sunday as it is steered around the southwestern portion of a deep-layer ridge near the southeastern United Stated coast. After landfall, Ida's forward motion is forecast to slow when it turns northward around the western extent of the aforementioned ridge. By Tuesday, the cyclone should reach the southern extent of the mid-latitude westerlies, causing it to turn north-northeastward across the Lower Mississippi and Tennessee Valleys. The track guidance has nudged slightly eastward during the first 12-24 hours, primarily due to the more northeastward initial position, and this has required a slight rightward adjustment in the new official forecast at those times. The remainder of the NHC forecast is largely unchanged from before, and lies near various consensus models and the GFS ensemble mean. 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. Rainfall impacts will also spread inland across the Lower Mississippi and Tennessee Valleys through early next week after Ida makes landfall. Key Messages: 1. There is a danger of life-threatening storm surge inundation Sunday along the coasts of Louisiana, Mississippi, and Alabama within the Storm Surge Warning area. Extremely life-threatening inundation of 9 feet or greater above ground level is possible somewhere within the area from Morgan City, Louisiana, to the coast of Mississippi. Overtopping of local levees outside of the Hurricane and Storm Damage Risk Reduction System is possible where local inundation values may be higher. Interests throughout the warning area should follow any advice given by local officials. 2. 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. 3. Damaging winds, especially in gusts, will spread inland near the track of the center of Ida across portions of southeastern Louisiana and southwestern Mississippi Sunday night and early Monday. These winds will likely lead to widespread tree damage and power outages. 4. Ida is likely to produce heavy rainfall Sunday into Monday across the central Gulf Coast from southeast Louisiana, coastal Mississippi, and far southwestern Alabama, resulting in considerable to life-threatening flash and urban flooding and significant river flooding impacts. As Ida moves inland, significant flooding impacts are possible across portions of the Lower Mississippi, Tennessee, and Ohio Valleys through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 26.2N 87.0W 90 KT 105 MPH 12H 29/0600Z 27.5N 88.6W 110 KT 125 MPH 24H 29/1800Z 29.1N 90.4W 115 KT 130 MPH 36H 30/0600Z 30.5N 91.3W 65 KT 75 MPH...INLAND 48H 30/1800Z 32.2N 91.2W 35 KT 40 MPH...INLAND 60H 31/0600Z 34.0N 90.1W 25 KT 30 MPH...INLAND 72H 31/1800Z 35.7N 88.1W 20 KT 25 MPH...INLAND 96H 01/1800Z 38.0N 82.5W 20 KT 25 MPH...POST-TROP/INLAND 120H 02/1800Z...DISSIPATED $$ Forecaster Brown |
