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Tropical Depression NINE Forecast Discussion (Text)


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000
WTNT44 KNHC 300854
TCDAT4

TROPICAL DEPRESSION NINE DISCUSSION NUMBER   7
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL092016
400 AM CDT TUE AUG 30 2016

Although there has been an increase in convection over the
southeastern portion of the depression's circulation, the system is
still being affected by westerly shear, with the low-level center
exposed to the west of the deep convection.  Recent observations
from a NOAA Hurricane Hunter aircraft and the unmanned NASA Global
Hawk indicate that the tropical cyclone remains just below tropical
storm strength.  The NOAA aircraft has reported peak flight level
winds in the southeastern quadrant of 32 kt, and believable SFMR
winds of around 30 kt.  A dropsonde from the Global Hawk reported
33 kt surface winds, but the mean-layer wind over the lowest 150 m
support winds closer to 30 kt.  A very recent center drop from the
unmanned aircraft indicate that the minimum pressure is 1003 mb.

The westerly shear over the depression is forecast to decrease
somewhat during the next day or so, however dry mid-level air is
expected to remain near and to the west of the system.  As a
result of the marginal environment, only gradual strengthening
is predicted during the next couple of days.  This is supported
by the global models which do not significantly deepen the system
until is moves over the western Atlantic and interacts with an
upper-level trough.  The NHC intensity forecast is unchanged from
the previous advisory and remains near the intensity consensus
model IVCN.

The aircraft fixes show that the depression has moved westward
since the previous advisory, and the initial motion estimate is
275/6 kt.  The cyclone is forecast to turn west-northwestward, then
northwestward tonight around a low- to mid-level ridge over
the western Atlantic and Florida.  After that time, a deepening
mid-latitude trough over the southeastern United States should
cause the system to turn northeastward toward the Florida Big
Bend region.  The dynamical models continue to agree on this
scenario, but there are some differences in the forward speed of
the system after 36 hours, and the NHC track is near the consensus
of the GFS and ECMWF models.  The more westward initial position has
required a westward adjustment to the track through 24 hours, but
otherwise, the new NHC track forecast is similar to the previous
advisory.

Given the current forecast, a tropical storm or hurricane watch may
be required for a portion of the Florida Gulf coast later today.


FORECAST POSITIONS AND MAX WINDS

INIT  30/0900Z 23.8N  86.6W   30 KT  35 MPH
 12H  30/1800Z 24.2N  87.3W   35 KT  40 MPH
 24H  31/0600Z 24.9N  87.6W   40 KT  45 MPH
 36H  31/1800Z 26.2N  86.9W   45 KT  50 MPH
 48H  01/0600Z 27.7N  85.5W   55 KT  65 MPH
 72H  02/0600Z 30.7N  81.1W   50 KT  60 MPH
 96H  03/0600Z 33.2N  74.0W   50 KT  60 MPH
120H  04/0600Z 35.5N  67.5W   50 KT  60 MPH

$$
Forecaster Brown



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Page last modified: Tuesday, 30-Aug-2016 08:54:13 UTC