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Tropical Storm Ida Forecast Discussion Number 3
2021-08-27 05:23:39| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Thu Aug 26 2021 000 WTNT44 KNHC 270322 CCA TCDAT4 Tropical Storm Ida Discussion Number 3...Corrected NWS National Hurricane Center Miami FL AL092021 1100 PM EDT Thu Aug 26 2021 Corrected Key Message Number 4 The Air Force Hurricane Hunters have been investigating Ida this evening and found maximum flight-level winds of 47 kt at 2500 ft. This data along with numerous unflagged 35-kt SFMR winds supported raising the intensity to 35 kt earlier this evening. Since the aircraft departed Ida, there has been little change in the storm's structure, so the initial intensity was held at 35 kt. Ida is an asymmetric tropical storm with most of the deep convection and stronger winds confined to the eastern half of the circulation. Both the NOAA and Air Force Hurricane Hunters will be investigating Ida Friday morning. The storm has been wobbling around, but smoothing through the recent erratic motion yields an initial motion estimate of 320/10 kt. A mid-level ridge centered off the southeast U.S. coast is expected to shift westward on Friday and over the weekend. This feature should keep Ida moving on a general northwestward track for the next 2 or 3 days, taking the core of the system over western Cuba Friday afternoon or evening and then across the southern and central Gulf of Mexico this weekend. Although some model timing differences remain, they are in fairly good agreement that Ida will make landfall in Louisiana late Sunday or early Monday. The GFS and ECMWF ensemble members basically span a similar region and are most concentrated across the state of Louisiana. Users are reminded to not focus on the exact forecast track as impacts will extend far from the center and the average 72-hour track error is around 120 miles. There is some southwesterly vertical wind shear affecting Ida at the moment, which is the likely part of the reason the cloud pattern and wind field are asymmetric. However, the global model show the upper-level pattern becoming quite favorable late Friday and through the weekend. These more conducive winds aloft combined with very warm SSTs and abundant moisture is likely to result in steady or rapid intensification until Ida makes landfall in the U.S. The intensity guidance unanimously show Ida becoming a hurricane, but there is notable spread in how strong the system will become. Given the expected favorable environmental conditions for the storm, the NHC intensity forecast lies near the high end of the model guidance, in best agreement with the regional hurricane models. It is also worth noting that even though the global models are not particularly accurate in predicting tropical cyclone winds, the GFS and ECMWF show the minimum pressure falling more than 35 mb from the current conditions. Based on all of this information, there is higher-than-normal confidence that a significant hurricane will be approaching the Gulf coast late this weekend. Key Messages: 1. Tropical storm conditions are expected in portions of the Cayman Islands tonight and in portions of western Cuba and the Isle of Youth Friday, where a dangerous storm surge is also possible in areas of onshore flow. 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 an increasing risk of life-threatening storm surge inundation along the coasts of Louisiana, Mississippi, and Alabama, where a Storm Surge Watch is in effect. Interests in these areas should follow any advice given by local officials. 3. There is an increasing risk of dangerous hurricane-force winds beginning Sunday along the portions of the coasts of Louisiana and Mississippi, including metropolitan New Orleans, where a Hurricane Watch is in effect. 4. Ida is likely to produce heavy rainfall Sunday into Monday along the central Gulf coast resulting in flash, urban, small stream, and riverine flooding. FORECAST POSITIONS AND MAX WINDS INIT 27/0300Z 18.6N 80.5W 35 KT 40 MPH 12H 27/1200Z 19.9N 82.0W 45 KT 50 MPH 24H 28/0000Z 21.8N 83.9W 55 KT 65 MPH...NEAR CUBA 36H 28/1200Z 23.8N 85.9W 65 KT 75 MPH 48H 29/0000Z 25.6N 88.0W 75 KT 85 MPH 60H 29/1200Z 27.3N 89.6W 85 KT 100 MPH 72H 30/0000Z 29.0N 90.6W 95 KT 110 MPH...NEAR THE COAST 96H 31/0000Z 32.0N 91.0W 45 KT 50 MPH...INLAND 120H 01/0000Z 33.9N 88.8W 25 KT 30 MPH...INLAND $$ Forecaster Cangialosi
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