[Tropical] Tropical Cyclone Discussion

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WTNT41 KNHC 170248
TCDAT1

TROPICAL DEPRESSION SIX DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062016
1100 PM AST TUE AUG 16 2016

Convective activity associated with the tropical wave and associated
low pressure area over the tropical Atlantic has become more
concentrated and better organized this evening, and a recent ASCAT
overpass indicates that the circulation has become better defined.
Based on these data, this system has been designated a tropical
depression, and advisories are being initiated at this time. The
initial wind speed of 30 kt is supported by the scatterometer data.
Some northeasterly shear is affecting the depression, with the
center located near the northeastern edge of the primary convective
mass.  The shear is forecast to decrease tonight and remain low
during the next couple of days which favors strengthening. However,
dry mid-level air is lurking just to the north of the depression,
and intrusions of this unfavorable airmass could arrest development.
The NHC forecast shows gradual strengthening during the next couple
of days, but it is on the lower side of the guidance, closest to the
LGEM and intensity consensus.  Later in the forecast period,
increasing southwesterly shear being produced by a mid- to
upper-level trough over the central Atlantic is likely to weaken the
tropical cyclone.

The initial motion estimate is a somewhat uncertain 310/12 kt.  The
depression is forecast to move generally northwestward into a
weakness in the subtropical ridge over the central Atlantic. The
track guidance is in relatively good agreement through 48 hours, but
there is a large spread between the GFS-based guidance and the ECMWF
later in the period. The ECMWF and the majority of its ensemble
members depict a much weaker and shallower cyclone that turns
west-northwestward in the low-level flow after 48 hours.  On the
other hand, the GFS, GFS ensemble mean, GFDL, and HWRF take a
stronger cyclone more poleward.  For now, the NHC track is between
these two distinct solutions, and is located just south of the
multi-model consensus at days 4 and 5.


FORECAST POSITIONS AND MAX WINDS

INIT  17/0300Z 12.6N  34.1W   30 KT  35 MPH
 12H  17/1200Z 13.7N  35.6W   35 KT  40 MPH
 24H  18/0000Z 15.2N  37.2W   40 KT  45 MPH
 36H  18/1200Z 16.8N  38.8W   45 KT  50 MPH
 48H  19/0000Z 18.1N  40.2W   50 KT  60 MPH
 72H  20/0000Z 20.0N  43.2W   50 KT  60 MPH
 96H  21/0000Z 22.5N  46.5W   45 KT  50 MPH
120H  22/0000Z 25.0N  50.0W   40 KT  45 MPH

$$
Forecaster Brown
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