000
WTNT43 KNHC 181442
TCDAT3
 
Potential Tropical Cyclone Three Discussion Number   4
NWS National Hurricane Center Miami FL       AL032021
1000 AM CDT Fri Jun 18 2021
 
The cyclone is gradually becoming better organized. Deep convection 
has increased during the past several hours, but it remains confined 
to the east side of the circulation due to about 20 kt of 
west-southwesterly wind shear.  The Air Force Hurricane Hunters have 
been investigating the system and they found a surface center a 
little to the east of where we previously expected it to be, but 
have otherwise reported generally light winds. Based on surrounding 
surface observations and the aircraft data, the initial intensity is 
held at 30 kt for this advisory. The leading edge of the rain is 
just reaching portions of the northern Gulf coast, and conditions 
will continue to deteriorate there through tonight.
 
The broad disturbance is moving north-northeastward at about 12 kt
into a weakness in the subtropical ridge.  This motion should
continue during the next 12 to 24 hours, taking the center of the
cyclone to the coast of southeastern Louisiana overnight or on
Saturday morning. After landfall, a turn to the right across the
southeast U.S. is expected when the system becomes embedded in the
westerly flow on the north side of the ridge.  The models are in
good agreement, and the NHC track forecast is a little to the east
of the previous one based on the initial position and motion.
 
Although the system will likely become a tropical storm later today 
or tonight, significant strengthening is not expected due to its 
broad and asymmetric structure, ongoing west-southwesterly shear, 
and limited time over the Gulf of Mexico waters.  The models are in 
quite good agreement overall, and the NHC intensity forecast lies 
near the HCCA and IVCN consensus aids.  It should be noted that the 
cyclone could be a little stronger at landfall than shown below 
since that is expected to occur between the 12- and 24-h forecast 
times.
 
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 today and
continuing through the weekend along the Central Gulf coast.   
Flood impacts will spread northeastward into the Southern 
Appalachians.
 
2. Tropical storm conditions are expected to begin later today in
areas near and well to the east of the center along portions of the
central Gulf Coast from Intracoastal City, Louisiana, to the
Okaloosa/Walton County line, Florida, including New Orleans.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  18/1500Z 26.5N  91.1W   30 KT  35 MPH...POTENTIAL TROP CYCLONE
 12H  19/0000Z 28.2N  90.9W   35 KT  40 MPH...TROPICAL CYCLONE
 24H  19/1200Z 30.3N  90.3W   35 KT  40 MPH...INLAND
 36H  20/0000Z 32.1N  88.9W   30 KT  35 MPH...INLAND
 48H  20/1200Z 33.4N  86.4W   25 KT  30 MPH...INLAND
 60H  21/0000Z 34.5N  83.8W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  21/1200Z...DISSIPATED
 
$$
Forecaster Cangialosi