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Potential Tropical Cyclone Three Discussion Number   2
NWS National Hurricane Center Miami FL       AL032021
1000 PM CDT Thu Jun 17 2021

Satellite imagery and data from an Air Force Reserve Hurricane 
Hunter aircraft indicate that the low pressure area over the 
southwestern Gulf of Mexico has changed little in organization 
during the past several hours, and the associated convection lies 
well to the east of the broad and poorly defined center.  The 
initial intensity will be held at 25 kt based partially on ship 
reports from the northeastern and northern parts of the system.

Due to the poorly defined center, the initial motion is a highly 
uncertain 360/8.  The system should move generally northward for 
the next 24-36 h to a position near the coast of Louisiana, 
followed by a motion toward the northeast across the southeastern 
United States as it moves through a weakness in the subtropical 
ridge caused by an upper-level trough over Texas, northern Mexico, 
and the adjacent Gulf of Mexico.  The forecast track is basically an 
update of the previous forecast.  It should be noted that the 
latest GFS run continues to forecast a re-formation of the center to 
the north sometime on Friday, and the forecast forward motion tries 
to account for this possibility.

The aforementioned upper-level trough is causing shear over the 
system, and present indications are that some shear will persist 
through landfall and hinder development.  The intensity forecast 
calls for the low to become a tropical cyclone in about 12 h, 
followed by some modest strengthening to tropical storm strength at 
24-36 h.  This would be followed by weakening over land, with the 
system dissipating over the southeastern United States between 72- 
96 h. There is a chance that, due to the interaction with the 
upper-level trough, the system may take on subtropical cyclone 
characteristics instead of tropical cyclone characteristics.  The 
new intensity forecast is similar to the previous forecast, and it 
lies at the upper edge of the intensity guidance envelope.
 
Given the current and anticipated structure of this system, users
should not focus on the exact track of the center, as rainfall and
wind hazards are likely to extend well east of the center and arrive
well in advance of landfall.
 
Key Messages:
 
1. The system is expected to produce heavy rainfall, considerable 
flash, urban and small stream flooding beginning Friday and 
continuing through the weekend along the Central Gulf coast, 
spreading northeastward into the Southern Appalachians.  
 
2. Tropical storm conditions are expected to begin Friday in areas
near and well to the east of the center along portions of the
central Gulf Coast from Intracoastal City, Louisiana, to the
Alabama/Florida border, including New Orleans.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/0300Z 23.5N  92.2W   25 KT  30 MPH...POTENTIAL TROP CYCLONE
 12H  18/1200Z 25.0N  92.4W   30 KT  35 MPH...TROPICAL CYCLONE
 24H  19/0000Z 27.2N  92.4W   35 KT  40 MPH
 36H  19/1200Z 29.8N  91.1W   40 KT  45 MPH...INLAND
 48H  20/0000Z 32.0N  88.8W   30 KT  35 MPH...INLAND
 60H  20/1200Z 34.1N  86.1W   25 KT  30 MPH...POST-TROP/INLAND
 72H  21/0000Z 35.6N  83.0W   20 KT  25 MPH...POST-TROP/INLAND
 96H  22/0000Z...DISSIPATED
 
$$
Forecaster Beven
 
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