Issued at 1000 PM CDT Thu Jun 17 2021

000
WTNT43 KNHC 180238
TCDAT3

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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