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Tropical Depression NINE Forecast Discussion


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000
WTNT44 KNHC 311442
TCDAT4

TROPICAL DEPRESSION NINE DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
1000 AM CDT WED AUG 31 2016

The system is producing vigorous deep convection, but there is
little organization to the overall cloud pattern.  Using the Dvorak
rules, a bursting but disorganized convective pattern would indicate
little change in strength.  The intensity is held at 30 kt pending
new observations from a NOAA Hurricane Hunter aircraft in a few
hours.  The tropical cyclone should be in a moderate shear
environment, and over very warm water, for the next 36 hours or so.
Therefore, strengthening is forecast and the official forecast
remains close to the intensity model consensus.  Given the
reasonably favorable environment, it is appropriate to maintain the
hurricane watch for the northeast Gulf coast at this time.  The
intensity forecast after 48 hours is problematic since the system
will be in a decidedly baroclinic environment and under strong
upper-level southwesterly flow.  This means that any intensification
that occurs in 2-3 days will likely have a contribution from
baroclinic processes.  By 96 hours, the global models depict the
system as embedded in a frontal zone, so extratropical transition is
forecast to occur by that time.

The center is very difficult to locate, but observations from a ship
suggest that there has been little motion since earlier this
morning, so the initial motion estimate is stationary.  There has
been little change to the track forecast guidance.  A 500-mb trough
over the southeastern United States should cause the cyclone to move
north-northeastward to northeastward across northern Florida and
southeastern Georgia during the next couple of days.  Later in the
forecast period there is uncertainty as to how far offshore the
center will move, with some of the global models such as the GFS
and the U.K. Met being close to the northeastern states, and the
ECMWF somewhat farther east.  The official track forecast lies
between these two possibilities.

It is important not to focus on the forecast landfall point of this
system.  Among other reasons, dangerous storm surge flooding is
likely to extend along the Gulf coast well to the east and south of
the path of the center.

FORECAST POSITIONS AND MAX WINDS

INIT  31/1500Z 24.6N  88.0W   30 KT  35 MPH
 12H  01/0000Z 25.9N  87.4W   40 KT  45 MPH
 24H  01/1200Z 27.3N  86.5W   45 KT  50 MPH
 36H  02/0000Z 29.0N  85.0W   55 KT  65 MPH
 48H  02/1200Z 30.9N  82.4W   50 KT  60 MPH...INLAND
 72H  03/1200Z 35.0N  75.0W   55 KT  65 MPH...OVER WATER
 96H  04/1200Z 38.0N  70.0W   55 KT  65 MPH...POST-TROP/EXTRATROP
120H  05/1200Z 40.0N  69.0W   55 KT  65 MPH...POST-TROP/EXTRATROP

$$
Forecaster Pasch