[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 040256
TCDAT5

Hurricane Dorian Discussion Number  43
NWS National Hurricane Center Miami FL       AL052019
1100 PM EDT Tue Sep 03 2019

Dorian's structure has changed significantly during the past day or
so.  Satellite and Doppler radar images show that the inner core has
become rather broad with a large ragged eye of at least 30 n mi
diameter.  Data from the Air Force Hurricane Hunters indicate
that the maximum winds and minimum pressure have held steady since
this afternoon, and based on that information, the initial
intensity is held at 95 kt, but this could be a little generous.
The aircraft data and surface observations indicate that the wind
field is expanding in size with tropical-storm-force and
hurricane-force winds extending up to 150 n mi and 50 n mi from the
center, respectively.  NOAA data buoy 41010 just northeast of the
center has been reporting sustained winds as high as 60 kt with
gusts to 78 kt, and seas over 30 ft.

Dorian is finally on the move again, and the latest initial motion
estimate is 340 degrees at 5 kt.  Dorian is being steered by the
flow between a mid-level ridge to the east and broad troughing to
its north.  A northwest to north motion with some increase in
forward speed is expected through Wednesday, taking the core of
Dorian just offshore and parallel to the east coast of Florida
during that time.  Thereafter, a faster motion toward the northeast
is predicted as a series of shortwave troughs move across the
northeastern U.S.  This should take the core of the hurricane
very near, or possibly over, the coasts of South and North Carolina
on Thursday and Friday.  After it passes the Outer Banks, the
hurricane is forecast to accelerate northeastward in the stronger
mid-latitude flow toward the Canadian Maritimes this weekend.
The NHC track forecast is largely unchanged and near the middle of
the tightly packed guidance envelope.

The hurricane is in a favorable environment of low wind shear, high
moisture, and warm SSTs, and it is expected to stay in these
conditions until it nears the Carolina coast.  Therefore, Dorian is
expected to remain about the same intensity during the next couple
of days.  After that time, an increase in shear from the
mid-latitude trough and drier air should cause Dorian to slowly
weaken.  The GFS and ECMWF models both show Dorian becoming an
extratropical system by 96 hours, and the official forecast follows
those solutions. As this system gains latitude, the wind field is
expected to expand even more.  Therefore, even if Dorian does not
make landfall, hurricane-force winds are expected to reach portions
of the coast from central Florida to North Carolina.

Key Messages:

1. Life-threatening storm surge and dangerous winds are expected
along portions of the Florida east coast and the coasts of Georgia,
South Carolina, and North Carolina, regardless of the exact track of
Dorian's center.  Water levels could rise well in advance of the
arrival of strong winds.  Residents in these areas should follow
advice given by local emergency officials.

2. The risk of wind and rain impacts along portions of the Virginia
coast and the southern Chesapeake Bay are increasing.  Residents in
these areas should continue to monitor the progress of Dorian.

3. The flash flood threat will increase overnight along the Florida
east coast, then spread up the southeast and mid Atlantic coast
beginning Wednesday.  There is a moderate risk of flash flooding
from coastal Georgia through the eastern portions of South and North
Carolina Wednesday and Thursday.


FORECAST POSITIONS AND MAX WINDS

INIT  04/0300Z 28.4N  79.0W   95 KT 110 MPH
 12H  04/1200Z 29.4N  79.6W   95 KT 110 MPH
 24H  05/0000Z 30.7N  79.9W   95 KT 110 MPH
 36H  05/1200Z 31.9N  79.5W   95 KT 110 MPH
 48H  06/0000Z 33.3N  78.2W   90 KT 105 MPH
 72H  07/0000Z 37.1N  72.1W   75 KT  85 MPH
 96H  08/0000Z 43.3N  62.7W   70 KT  80 MPH...POST-TROP/EXTRATROP
120H  09/0000Z 51.5N  52.2W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
Forecaster Cangialosi
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