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| #1058869 (Received by flhurricane at: 10:53 AM 27.Aug.2021) TCDAT4 Tropical Storm Ida Discussion Number 5 NWS National Hurricane Center Miami FL AL092021 1100 AM EDT Fri Aug 27 2021 Radar imagery from Grand Cayman and Cuba as well as satellite data continue to show an improvement in Ida's overall structure this morning, with an increase in banding, the development of a small central dense overcast, and more recently an improved inner-core feature. Both the NOAA and Air Force reconnaissance aircraft reported that the pressure has fallen to around 996 mb, and the Air Force plane has measured flight-level and SFMR winds that support an initial intensity of 55 kt. Although there is still some southwesterly shear over Ida, the outflow has begun to expand over the northeastern and southeastern portions of the circulation. The upper-level trough near the Yucatan peninsula that has been imparting the shear over Ida is forecast to weaken and move westward during the next 12 to 24 hours, which should result in a more favorable upper-level wind pattern. This, in combination with warm sea surface temperatures and a moist environment along the forecast track of the storm are expected to result in steady to rapid strengthening. Ida is now foreast to become a hurricane when it is near western Cuba and once it moves over the southeastern Gulf of Mexico a period of rapid strengthening is likely to begin, with the NHC intensity forecast explicitly calling for rapid intensification to major hurricane strength between 24 and 48 hours. The official intensity forecast is on the higher side of the intensity guidance but not quite as high as the slightly more aggressive CTCI, HWRF, and HCCA models. In addition to the increase in strength, the dynamical model guidance indicates that Ida's wind field will grow larger as it moves over the Gulf of Mexico and this is reflected in the NHC wind radii forecast. In summary, there is a higher-than-normal confidence that a significant hurricane will impact a large portion of the northern Gulf coast by late this weekend and early next week. Ida is moving northwestward or 320/13 kt. The track forecast reasoning is unchanged from before. A mid-level ridge over the western Atlantic is forecast to move westward and this should keep Ida on a general northwestward heading during the next 48-60 hours. This track will bring the storm across western Cuba later today, over the southeastern and central Gulf of Mexico on Saturday and Saturday night, to the coast of Louisiana by late Sunday. The track guidance is in remarkably good agreement with very little cross-track spread during the first 60 hours or so of the forecast period. After that time, Ida is forecast to reach the western portion of the ridge, which is expected to cause the storm to slow down and turn northward and then northeastward over the southeastern United States. The NHC track forecast is near or just east of the various consensus aids, in best agreement with the GFS ensemble mean. Although the small spread in the guidance through landfall increases the overall confidence in the track forecast, users are reminded to not focus on the exact details of the forecast track 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 later today and 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. The risk of life-threatening storm surge inundation is increasing along the coasts of Louisiana, Mississippi, and Alabama. Inundation of 7 to 11 feet above ground level is possible within the area from Morgan City, Louisiana, to Ocean Springs, Mississippi, including Lake Borgne. Interests in these areas should follow any advice given by local officials. 3. Ida is expected to be a dangerous major hurricane when it reaches the northern Gulf Coast on Sunday, and the risk of hurricane-force winds continues to increase, especially along portions of the Louisiana coast, including metropolitan New Orleans. Potentially devastating wind damage could occur where the core of Ida moves onshore. 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, as well as the Lower Mississippi Valley, resulting in considerable flash, urban, small stream, and riverine flooding. FORECAST POSITIONS AND MAX WINDS INIT 27/1500Z 20.7N 82.1W 55 KT 65 MPH 12H 28/0000Z 22.2N 83.7W 65 KT 75 MPH...OVER WESTERN CUBA 24H 28/1200Z 24.0N 85.8W 75 KT 85 MPH...OVER WATER 36H 29/0000Z 25.9N 87.8W 90 KT 105 MPH 48H 29/1200Z 27.6N 89.7W 105 KT 120 MPH 60H 30/0000Z 29.0N 90.8W 105 KT 120 MPH 72H 30/1200Z 30.3N 91.3W 60 KT 70 MPH...INLAND 96H 31/1200Z 33.3N 90.2W 30 KT 35 MPH...INLAND 120H 01/1200Z 35.2N 87.1W 20 KT 25 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown |
