880 
WTNT43 KNHC 172034
TCDAT3
 
Potential Tropical Cyclone Three Discussion Number   1
NWS National Hurricane Center Miami FL       AL032021
400 PM CDT Thu Jun 17 2021
 
Visible satellite images show that the cloud pattern associated with 
the broad area of low pressure located over the southwestern Gulf of 
Mexico is gradually becoming better organized.  Deep convection is 
beginning to form a broad curved band over the eastern portion of 
the system, similar to what one might see in a developing 
subtropical cyclone.  Although the upper-level winds are not 
particularly favorable for development, with lots of westerly shear 
over the area, the global models do suggest tropical/subtropical 
cyclogenesis within the next 12 hours or so.  Given the proximity of 
the disturbance to land, which requires tropical storm warnings at 
this time, advisories are being initiated on this system as a  
potential tropical cyclone. 
 
Earlier scatterometer data suggested that the circulation was still
rather broad.  An Air Force Hurricane Hunter plane is currently
investigating the system and has not yet found a well-defined
center.  Maximum winds based on surface observations and the
scatterometer pass are near 25 kt.  Numerical intensity guidance do
not indicate a great deal of strengthening before the system
reaches the coastline, and the official forecast is at the high end
of the guidance.
 
Since the center is not that well-defined at this time, the initial
motion estimate, 360/8 is quite uncertain.  The system is expected
to move northward into a weakness in the subtropical ridge for the 
next day or so and then, after landfall along the central Gulf 
Coast, turn toward the northeast on the northwest side of a
mid-level anticyclone near Florida.  The official track forecast is
closest to the GFS and ECMWF predictions.  It should be noted,
however, that these models suggest some reformation of the center
near the Louisiana coast rather than just motion from the southwest
Gulf to the expected coastal landfall point.

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 and considerable 
flash, urban, and small stream flooding beginning Friday and 
continuing through the weekend along the central Gulf coast and 
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  17/2100Z 22.9N  92.4W   25 KT  30 MPH...POTENTIAL TROP CYCLONE
 12H  18/0600Z 24.5N  92.5W   25 KT  30 MPH...TROPICAL CYCLONE
 24H  18/1800Z 26.5N  92.5W   35 KT  40 MPH
 36H  19/0600Z 29.0N  92.0W   40 KT  45 MPH
 48H  19/1800Z 31.5N  89.5W   30 KT  35 MPH...INLAND
 60H  20/0600Z 34.0N  87.0W   25 KT  30 MPH...INLAND
 72H  20/1800Z 35.0N  84.0W   20 KT  25 MPH...INLAND
 96H  21/1800Z...DISSIPATED
 
$$
Forecaster Pasch/Brennan