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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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