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Hurricane Zeta Forecast Discussion Number 17
2020-10-28 22:00:35| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Wed Oct 28 2020 000 WTNT43 KNHC 282100 TCDAT3 Hurricane Zeta Discussion Number 17 NWS National Hurricane Center Miami FL AL282020 400 PM CDT Wed Oct 28 2020 The center of Zeta is in the Terrebone Bay area of Louisiana and is making landfall near Cocodrie. Somewhat surprisingly, Zeta has rapidly intensified this afternoon. Although the hurricane has been moving over marginally warm SSTs and relatively low heat content waters, it has intensified from 80 kt to 95 kt in about 6 hours. It is possible that this intensification can be at least partly attributable to a conducive interaction with with an upper-level trough located a few hundred miles to the west-northwest of Zeta. The 95-kt intensity estimate for Zeta is based on a blend of flight-level, SFMR and dropsonde winds from an Air Force Reserve Hurricane Hunter aircraft. Since the center will either be interacting with land or moving over land from this point, a weakening trend should begin tonight. The official intensity forecast is close to the Decay-SHIPS guidance, which should handle the exponential decay of wind seed for tropical cyclones moving over land. In 24 hours or so, the global models depict the system as being embedded in a front while it approaches the United States east coast. Thus the official forecast shows an extratropical cyclone at that point and beyond. After 48 hours, the models show the low becoming elongated and absorbed into the frontal zone. Zeta has turned toward the north-northeast and the forward speed is increasing, with the motion now 025/21 kt. The cyclone should accelerate north-northeastward ahead of a 500-mb trough through tonight. The system should then move even faster toward the northeast, ahead of the trough, and across the southeastern and eastern United States on Thursday. Post-tropical Zeta should move east-northeastward, in the mid-level westerlies, into the Atlantic Friday morning. The official track forecast follows the correct model consensus, HCCA, rather closely. Given Zeta's acceleration after landfall, strong winds are likely to spread well inland over the southeastern U.S. overnight and early Thursday. KEY MESSAGES: 1. A life-threatening storm surge is beginning along portions of the northern Gulf Coast, with the highest inundation expected to occur somewhere between Port Fourchon, Louisiana, and Dauphin Island, Alabama, especially along the Mississippi coast. Overtopping of local, non-federal levee systems is possible within southeastern Louisiana outside of the Hurricane and Storm Damage Risk Reduction System. 2. Extremely dangerous hurricane conditions are spreading across portions of the Hurricane Warning area along the southeastern Louisiana coast and will spread to the Mississippi coast this evening. Tropical storm conditions will spread into portions of the Tropical Storm Warning area along the Alabama and far western Florida Panhandle coasts in the next few hours. 3. Strong, damaging wind gusts, which could cause tree damage and power outages, will spread well inland across portions of southeastern Mississippi, Alabama, northern Georgia, the Carolinas, and southeastern Virginia tonight and Thursday due to Zeta's fast forward speed. Wind gusts could be especially severe across the southern Appalachian Mountains on Thursday. 4. Through Thursday, heavy rainfall is expected from portions of the central U.S. Gulf Coast into the Mid-Mississippi Valley, Ohio Valley, southern to central Appalachians, and Mid-Atlantic States near and in advance of Zeta. This rainfall will lead to flash, urban, small stream, and minor river flooding. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 29.2N 90.6W 95 KT 110 MPH...ON THE COAST 12H 29/0600Z 32.8N 87.0W 55 KT 65 MPH...INLAND 24H 29/1800Z 37.5N 78.8W 40 KT 45 MPH...POST-TROP/INLAND 36H 30/0600Z 41.0N 68.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 48H 30/1800Z 44.0N 57.0W 45 KT 50 MPH...POST-TROP/EXTRATROP 60H 31/0600Z...DISSIPATED $$ Forecaster Pasch
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