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Tropical Depression NINE Forecast Discussion


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000
WTNT44 KNHC 310256
TCDAT4

TROPICAL DEPRESSION NINE DISCUSSION NUMBER  10
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
1000 PM CDT TUE AUG 30 2016

The convective organization of the cyclone has improved markedly
since this time yesterday, and especially since the previous
advisory, with a large convective cloud mass having developed around
the well-defined low-level center. Ship C6FN5 located about 80 nmi
south of the center at 00Z reported a 35-kt wind, but at an elevated
height of 43 meters, which adjusts down to a 10-meter wind of 30-31
kt. The recent NOAA recon flight also confirmed that winds of about
30 kt existed, so the intensity will remain unchanged at 30 kt for
this advisory.

Fixes from the NOAA aircraft indicated a west-southwestward motion
over the previous 6 hours. However, this is believed to be a
temporary motion that was likely just the result of the center
redeveloping closer to strongest convection in the southern
quadrant. Since that time, little motion or just a slight drift
toward the north-northwest at 2 kt is indicated by satellite
imagery. The latest 00Z upper-air data showed the depression is now
located along or just north of the subtropical ridge axis that is
oriented east-west across the Florida Straits, a steering pattern
that favors a northward motion during the next 12 hours or so. After
that time, the NHC model guidance is in excellent agreement on a
shortwave trough currently over the central U.S. digging
southeastward to the northeast Gulf coast and lifting out and
accelerating the cyclone toward the northeast by 36 hours. Due to
the uncertainty in the short term motion, the new official forecast
was not shifted as far west as the latest model consensus and
instead lies very close to the previous advisory track.

Unlike the previous several days, deep convection has finally
developed north of the low-level center during the past 6 hours,
and more recent satellite trends suggest that some inner-core
curved banding features may be developing. The upper-level outflow
has been improving and expanding in all quadrants now that the
vertical wind shear has decreased to less than 10 kt and has shifted
from a northerly to a westerly component. Some additional decrease
in the shear is forecast to occur for the next 36 to 48 hours while
the cyclone remains in a modestly moist environment. The NHC
intensity guidance has increased as a result of the improving
environmental conditions, so the official intensity forecast has
also been increased, which now shows the cyclone near hurricane
strength just prior to landfall at 48 hours. No changes to the
existing hurricane and tropical storm watches are required at this
time. However, by Wednesday morning, a tropical storm watch may be
needed for the coasts of northeast Florida and Georgia.

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

FORECAST POSITIONS AND MAX WINDS

INIT  31/0300Z 24.3N  87.8W   30 KT  35 MPH
 12H  31/1200Z 25.1N  87.7W   40 KT  45 MPH
 24H  01/0000Z 26.3N  87.0W   45 KT  50 MPH
 36H  01/1200Z 27.8N  85.9W   50 KT  60 MPH
 48H  02/0000Z 29.6N  83.9W   60 KT  70 MPH
 72H  03/0000Z 33.4N  77.5W   60 KT  70 MPH
 96H  04/0000Z 37.1N  70.0W   60 KT  70 MPH
120H  05/0000Z 39.0N  68.2W   60 KT  70 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart