ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
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.
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