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Hurricane Ida Forecast Discussion Number 15
2021-08-29 22:52:12| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Sun Aug 29 2021 000 WTNT44 KNHC 292052 TCDAT4 Hurricane Ida Discussion Number 15 NWS National Hurricane Center Miami FL AL092021 400 PM CDT Sun Aug 29 2021 NWS Doppler radar imagery and data from an Air Force Reserve Reserve Hurricane Hunter aircraft showed that Ida made landfall around 1655 UTC along the southeastern coast of Louisiana near Port Fourchon with estimated maximum winds of 130 kt and a minimum pressure around 930 mb. Since that time, Ida made a second landfall southwest of Galliano, Louisiana, and with the eyewall now onshore weakening has begun. Based on the latest Doppler velocities the initial wind speed has been conservatively reduced to 115 kt for this advisory. As Ida's circulation moves farther inland this evening and overnight a faster rate of weakening is expected, and Ida is forecast to become a tropical depression over Mississippi by late Monday. Although weakening is forecast, damaging winds, especially in gusts, are expected to spread inland over southeastern Louisiana and southwestern Mississippi through Monday morning. To account for this, the gust factor in the Forecast/Advisory has been adjusted accordingly. By 72 hours, Ida is predicted to merge with a frontal zone over the eastern United States and become an extratropical low, and this low is forecast to strengthen into a gale center near Atlantic Canada by the end of the forecast period. Radar fixes indicate that Ida's forward motion has slowed and the initial motion estimate is 325/9 kt. The hurricane should turn northward tonight around the western periphery of a deep-layer ridge near the southeastern United States coast. Ida is forecast to turn northeastward and recurve over the eastern United States as it enters the mid-latitude westerlies. The GFS is a bit faster in ejecting the post-tropical cyclone northeastward on days 3 through 5, and the NHC forecast follows a blend of the various consensus models and the GFS ensemble mean. Key Messages: 1. Extremely life-threatening storm surge inundation of 9 feet or greater above ground level will continue through early this evening along portions of the coast between Burns Point, Louisiana, to Ocean Springs, Mississippi. Overtopping of local levees outside of the Hurricane and Storm Damage Risk Reduction System is possible where local inundation values may be higher. 2. Catastrophic wind damage will occur near the core of Ida as it moves inland over southeastern Louisiana during the next few hours. Hurricane-force winds and damaging wind gusts are expected through tonight within the Hurricane Warning area in southeastern Louisiana, including metropolitan New Orleans. 3. Damaging winds, especially in gusts, will spread inland near the track of the center of Ida into southwestern Mississippi tonight and early Monday. These winds will likely lead to widespread tree damage and power outages. 4. Ida will continue to produce heavy rainfall through Monday across the central Gulf Coast across southeast Louisiana, coastal Mississippi, and 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 Valley, Tennessee Valley, Upper Ohio Valley, Central Appalachians, and Mid-Atlantic through Wednesday. FORECAST POSITIONS AND MAX WINDS INIT 29/2100Z 29.5N 90.6W 115 KT 130 MPH...INLAND 12H 30/0600Z 30.7N 90.9W 65 KT 75 MPH...INLAND 24H 30/1800Z 32.4N 90.7W 35 KT 40 MPH...INLAND 36H 31/0600Z 34.0N 89.4W 25 KT 30 MPH...INLAND 48H 31/1800Z 35.6N 87.2W 25 KT 30 MPH...INLAND 60H 01/0600Z 37.1N 84.2W 20 KT 25 MPH...POST-TROP/INLAND 72H 01/1800Z 38.6N 80.5W 20 KT 25 MPH...POST-TROP/EXTRATROP 96H 02/1800Z 41.3N 72.5W 30 KT 35 MPH...POST-TROP/EXTRATROP 120H 03/1800Z 43.8N 67.0W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Brown
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