[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 030854
TCDAT5

Hurricane Dorian Discussion Number  40
NWS National Hurricane Center Miami FL       AL052019
500 AM EDT Tue Sep 03 2019

Dorian continues to pound Grand Bahama Island early this morning
while moving little.  The eyewall has become a little less
defined over the past few hours on radar.  On infrared satellite
images, the eye remains fairly well defined, but the surrounding
deep convection is somewhat fragmented.  Upper-level outflow is a
bit restricted over the western semicircle of the circulation.  The
initial intensity is held at 105 kt, which is a blend of subjective
Dvorak data-T numbers from TAFB and SAB.  Dorian is expected to more
or less maintain its intensity for about 36 hours. After that time
period, increasing vertical shear should cause gradual weakening.
However, the system is likely to remain a major hurricane for the
next few days.  The official forecast is closest to the latest LGEM
guidance.

Dorian has been nearly stationary for the past 18 hours, as
steering currents in its vicinity have collapsed.  The global
models indicate that a weakness in the subtropical ridge will
develop in response to a trough that will amplify along the east
coast of the United States within the next day or so.  Dorian
should respond to these changes by beginning to move
north-northwestward toward the weakness in the ridge a little later
today.  The system should turn northward with a gradual increase in
forward speed as it moves through the weakness in around 48 hours.
Later in the period, the cyclone should accelerate northeastward on
the southern side of the trough.  The official track forecast is
similar to the previous one, and is fairly close to the model
consensus.

Although the official forecast does not show Dorian making landfall
along the Florida east coast, users are reminded not to forecast on
the exact forecast track.  A relatively small deviation to the
left of this track could bring the core of the hurricane near or
over the coastline.


Key Messages:

1. Devastating winds and storm surge will continue to affect Grand
Bahama Island for several more hours.  Everyone there should remain
in shelter.

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

3. The risk of life-threatening storm surge and hurricane-force
winds continues to increase along the coast of North Carolina.
Residents in these areas should follow advice given by local
emergency officials.

4. The flash flood threat will increase today and tonight along the
Florida peninsula, then spread up the southeast and mid-Atlantic
coast during the middle and latter part of the week.


FORECAST POSITIONS AND MAX WINDS

INIT  03/0900Z 26.9N  78.4W  105 KT 120 MPH
 12H  03/1800Z 27.5N  78.8W  105 KT 120 MPH
 24H  04/0600Z 28.5N  79.3W  105 KT 120 MPH
 36H  04/1800Z 29.9N  79.7W  105 KT 120 MPH
 48H  05/0600Z 31.4N  79.4W  100 KT 115 MPH
 72H  06/0600Z 34.3N  76.6W   85 KT 100 MPH
 96H  07/0600Z 39.0N  69.3W   75 KT  85 MPH
120H  08/0600Z 46.5N  59.5W   70 KT  80 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch
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