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Potential Tropical Cyclone THREE (Text)


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Potential Tropical Cyclone Three Discussion Number   6
NWS National Hurricane Center Miami FL       AL032021
1000 PM CDT Fri Jun 18 2021

Satellite imagery indicates that the circulation associated with 
the broad low pressure area over the northern Gulf of Mexico is 
slowly getting better defined, and several swirls of low-level 
clouds/vorticity centers were apparent in visible imagery just 
before dark.  However, surface data and reports from an Air Force 
Reserve Hurricane Hunter aircraft show that the surface wind field 
is more like a trough elongated NNE-SSW from southeastern 
Louisiana into the Gulf.  In addition, the convection associated 
with the system is mostly well to the northeast of the swirls.  
Based on this, the low will remain as a potential tropical cyclone, 
as it has not yet put all of the pieces together to be called a 
tropical or subtropical cyclone.

There is again little change to the track forecast reasoning.  The 
initial motion is a little slower than before at 010/11.  This 
general motion should continue until the system reaches the 
northern Gulf coast in the next 6 h or so.  After the system
moves inland, a turn to the northeast and then east-northeast
across the southeast U.S. is predicted when the cyclone becomes
embedded in the westerlies on the north side of the subtropical
ridge.  The new forecast is a little faster and a little south of 
the previous forecast after 36 h based on the latest guidance, but 
other than that there are no significant changes.

Time is running out for the system to develop further before 
landfall.  However, it should be noted that in this case landfall 
will not instantly put an end to the chances of tropical or 
subtropical cyclone development, as much of the associated strong 
winds and convection will remain over water for at least 12 h.  
After that time, the system should be far enough inland to 
cause weakening to start. One note is that all of the global models 
except the GFS now forecast the low to survive for more than 72 h.  
The new intensity forecast will not change the dissipation time for 
now.  However, if the 00Z global models continue this trend, 
subsequent advisories may need to show a longer life for the system.
 
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.  Impacts 
along the northern Gulf coast will continue regardless of whether 
there is any additional development.
 
Key Messages:
 
1. The system is expected to produce heavy rainfall and 
considerable flash, urban and small stream flooding, continuing 
through the weekend along the central Gulf Coast, with flood 
impacts spreading northeastward into the southern Appalachians and 
portions of the Southeast.  
 
2. Tropical storm conditions are occurring along portions of the
central Gulf Coast from east of Morgan City, Louisiana, to the
Okaloosa/Walton County line, Florida, including New Orleans.  These
winds will spread inland and continue into Saturday.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  19/0300Z 28.9N  90.9W   40 KT  45 MPH...POTENTIAL TROP CYCLONE
 12H  19/1200Z 30.4N  90.3W   40 KT  45 MPH...INLAND
 24H  20/0000Z 31.9N  88.5W   30 KT  35 MPH...INLAND
 36H  20/1200Z 33.2N  85.9W   25 KT  30 MPH...INLAND
 48H  21/0000Z 34.1N  82.8W   25 KT  30 MPH...INLAND
 60H  21/1200Z 35.5N  79.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 72H  22/0000Z...DISSIPATED
 
$$
Forecaster Beven
 
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Page last modified: Tuesday, 26-Oct-2021 12:09:05 UTC