[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT43 KNHC 180855
TCDAT3

Potential Tropical Cyclone Three Discussion Number   3
NWS National Hurricane Center Miami FL       AL032021
400 AM CDT Fri Jun 18 2021

The system became a little better organized overnight at the
northern end of its associated broad surface trough over the central
Gulf of Mexico.  Satellite images show increasing deep convection
along with more curvature to the low clouds, suggesting that the
ill-defined center of this system is trying to re-form farther to
the north. Since it still lacks a well-defined center, the system
remains a potential tropical cyclone.  Recent scatterometer data
indicate that winds have increased to at least 30 kt and have grown
over a larger area on the east side of the circulation.

The initial motion is a highly uncertain 360/12.  There is fair
agreement that this northward motion, with some re-formation of the
center, will continue as the system remains steered by a
subtropical ridge to the southeast.  The low should then turn
northeastward and move across the southeastern U.S.  No
significant changes were made to the previous track forecast and
the guidance is in fairly good agreement. It should also be noted
that model "spaghetti" plots are not doing a good job tracking the
center of this system, and could give a very misleading impression
on the forecast track if used by themselves.

There is still a lot of shear over the Gulf of Mexico and that
should continue through landfall.  However, the system is somewhat
hybrid in nature and the shear shouldn't prevent its intensification
to a tropical storm later today (possibly with subtropical
characteristics).  Model guidance is consistent with slow
strengthening until landfall, and the new forecast is close to the
previous one.  After landfall, most of the global models show a
strong band of heavy rain and tropical-storm-force winds persisting
on the southeastern side.  The expected large distance from the
center necessitates extending the Tropical Storm Warning into the
northwestern Florida panhandle.  The system will likely dissipate in
about 3 days over the southeastern United States.

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 with
flood impacts spreading northeastward into the Southern
Appalachians.

2. Tropical storm conditions are expected to begin 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  18/0900Z 25.2N  91.5W   30 KT  35 MPH...POTENTIAL TROP CYCLONE
 12H  18/1800Z 27.0N  91.5W   35 KT  40 MPH...TROPICAL CYCLONE
 24H  19/0600Z 29.2N  91.2W   40 KT  45 MPH
 36H  19/1800Z 31.0N  89.5W   35 KT  40 MPH...INLAND
 48H  20/0600Z 32.6N  87.6W   25 KT  30 MPH...INLAND
 60H  20/1800Z 34.5N  85.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
 72H  21/0600Z...DISSIPATED

$$
Forecaster Blake
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