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Hurricane Ida Forecast Discussion Number 6
2021-08-27 22:49:28| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Fri Aug 27 2021 000 WTNT44 KNHC 272049 TCDAT4 Hurricane Ida Discussion Number 6 NWS National Hurricane Center Miami FL AL092021 500 PM EDT Fri Aug 27 2021 Cuban radar data and reports from an earlier Air Force Reserve Hurricane Hunter mission indicate that Ida's inner core structure continued to improve after the release of the previous advisory package. An eye became apparent in radar imagery before the center reached the Isle of Youth, and the final fix from the Air Force Hurricane Hunter aircraft reported a closed 24-n-mi wide eye. The aircraft measured winds to support hurricane intensity shortly before 1800 UTC, and during the final northeast eyewall pass, and flight-level wind data support increasing the intensity to 70 kt, which is used as the initial intensity for this advisory. The upper-level outflow has expanded over all but the southwestern portion of the circulation, and the upper-level wind pattern is forecast to continue to improve overnight and early Saturday. Once Ida moves past western Cuba and into the southeastern Gulf of Mexico, it will be moving through a very favorable oceanic and atmospheric environment consisting of high ocean heat content waters, low vertical wind shear, and a moist low- to mid-level atmosphere. These conditions are likely to result in a period of rapid strengthening during the next 24 to 36 hours. In fact, with the higher initial wind speed, the intensity guidance has significantly increased this cycle, and the bulk of the guidance now brings Ida to category 4 intensity. The NHC forecast explicitly calls for rapid intensification during the next 24 to 36 hours, which is supported by several of the dynamical models, the LGEM model, and high probabilities of rapid intensification indicated by the SHIPS and DTOPS RI guidance. The NHC forecast is near the IVCN multi-model consensus aid, but is lower than HCCA and LGEM. It should be noted that some fluctuations in intensity are possible as Ida nears the northern Gulf coast due to possible eyewall replacement cycles. In addition to the expected increase in strength, the dynamical model guidance again calls for Ida's wind field to expand while it moves over the Gulf of Mexico. As a result, there is higher-than-normal confidence that a large and powerful hurricane will impact portions of the northern Gulf coast by late this weekend and early next week. Ida has wobbled a little right of the previous track, but the longer term motion continues to be northwestward or 320/13 kt. The steering currents remain well-established as a strong deep-layer ridge over the western Atlantic should continue to steer Ida northwestward across the Gulf this weekend. Ida will approach the western portion of the ridge after landfall, and this should result in a slower northward motion by day 3. After that time, a short-wave trough over the central United States is expected to cause the system to turn northeastward. The track guidance remains in remarkably good agreement through landfall along the northern Gulf coast, and there is higher-than-normal confidence in that portion of the track forecast. However, 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. Key Messages: 1. Life-threatening storm surge and hurricane conditions are expected to continue through tonight in portions of western Cuba, including the Isle of Youth, where a Hurricane Warning is in effect. Life-threatening heavy rains, flash flooding and mudslides are expected across Jamaica, the Cayman Islands, and western Cuba, including the Isle of Youth. 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 and Alabama, resulting in considerable flash, urban, small stream, 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 27/2100Z 22.1N 83.2W 70 KT 80 MPH 12H 28/0600Z 23.5N 84.8W 85 KT 100 MPH 24H 28/1800Z 25.3N 86.9W 105 KT 120 MPH 36H 29/0600Z 27.1N 89.0W 115 KT 130 MPH 48H 29/1800Z 28.6N 90.6W 120 KT 140 MPH 60H 30/0600Z 30.0N 91.3W 80 KT 90 MPH...INLAND 72H 30/1800Z 31.5N 91.1W 40 KT 45 MPH...INLAND 96H 31/1800Z 34.4N 89.3W 30 KT 35 MPH...INLAND 120H 01/1800Z 36.0N 86.0W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown
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