[Tropical] Tropical Cyclone Discussion

[EMWIN Server]

WTNT44 KNHC 132043
TCDAT4

Tropical Depression Nine Discussion Number   5
NWS National Hurricane Center Miami FL       AL092019
500 PM EDT Fri Sep 13 2019

An Air Force plane extensively investigated the disturbance near the
Bahamas during the past several hours, and in the last portion of
the mission, the crew was able to locate a center of circulation,
although weak, near the convection.  The center was a little bit
to the east of the previous estimates. Satellite images also
indicate that the cloud pattern has become a little better organized
and Dvorak estimates are T2.0 and 1.5 from TAFB and SAB,
respectively. On this basis, the disturbance has been classified as
a tropical depression with 25 kt winds.

Conditions are not ideal for strengthening since the depression
is still embedded within a moderate shear environment, but
this parameter is not expected to be strong enough to halt
additional development. The NHC forecast still calls for this system
to become a tropical storm on Saturday with gradual intensification
thereafter.  Global models insist on further development, and the
reliable guidance suggests that the cyclone could even reach
hurricane intensity in about 3 days, and so does the NHC forecast.
By then, the system is expected to be over the Atlantic waters well
southeast of the coast of the Carolinas.

Due to the reformation of the apparent center, the initial motion is
highly uncertain. The best estimate is toward the northwest or 305
degrees at 7 kt.   A weakness in the ridge over the western Atlantic
is forecast to develop, and this pattern should steer the system
slowly toward the northwest and then northward. In about 3 days, an
eastward moving mid-latitude trough will force the system to recurve
away from the coast toward the Atlantic.  The track guidance has
shifted to the east again, and this shift is larger due to the
eastward formation of the center. Consequently, the NHC track
forecast was adjusted in that direction, but it remains on the
western edge of the guidance envelope.

Key Messages:

1. The depression is forecast to become a tropical storm within
the next 24 hours and will likely bring tropical-storm-force winds
and heavy rainfall to portions of the northwestern Bahamas later
today and Saturday. Significant storm surge is not expected in the
northwest Bahamas from this system. Residents there should follow
any advice given by local officials.

2. The system could still bring tropical storm conditions to
portions of the Florida east coast. Residents there should monitor
the progress of this system and follow any advice given by local
officials.

3. Heavy rainfall and scattered flash flooding is possible this
weekend in coastal sections of eastern Florida, Georgia, and South
Carolina. The chance of heavy rainfall affecting coastal North
Carolina early next week continues to diminish.


FORECAST POSITIONS AND MAX WINDS

INIT  13/2100Z 25.6N  75.0W   25 KT  30 MPH
 12H  14/0600Z 26.2N  76.0W   30 KT  35 MPH
 24H  14/1800Z 27.4N  77.6W   35 KT  40 MPH
 36H  15/0600Z 28.8N  78.5W   45 KT  50 MPH
 48H  15/1800Z 30.0N  78.8W   55 KT  65 MPH
 72H  16/1800Z 31.5N  76.5W   65 KT  75 MPH
 96H  17/1800Z 32.0N  73.0W   70 KT  80 MPH
120H  18/1800Z 32.5N  68.0W   75 KT  85 MPH

$$
Forecaster Avila
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