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TROPICAL DEPRESSION SIX SPECIAL DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL062015
130 AM AST SUN AUG 30 2015

The well-defined low pressure system located to the west of Conakry,
Guinea, has acquired sufficient organized convection to be
classified as a tropical depression. The initial intensity of 30 kt
is based on a Dvorak satellite intensity estimate of T2.0/30 kt
from TAFB and two earlier ASCAT scatterometer passes indicating at
least 30 kt in the southern semicircle.

The initial motion estimate is 305/10 kt. The depression is
located south of a deep-layer subtropical ridge that extends
westward across northwestern Africa and into the eastern Atlantic
for several hundred miles. However, a weakness is located in a
portion of the ridge to the north of the Cape Verde Islands due to
a pronounced mid-latitude trough noted in water vapor imagery
digging east-southeastward. This should allow the cyclone to move
northwestward toward the Cape Verde Islands through 48 hours. After
that time, the NHC model guidance is in fair agreement on the
aforementioned trough lifting out, allowing the ridge to build
back in, which is expected to force the cyclone on a more westward
track. The NHC track forecast lies close to the consensus models
TVCA and GFEX.

The depression is embedded within favorable environmental and
oceanic conditions consisting of low vertical wind shear of less
than 10 kt, a moist mid-troposphere, and sea-surface temperatures
greater than 28 deg C, which should allow for steady strengthening
for the next 48 hours or so. The main inhibiting factor is the
decreasing instability ahead of the cyclone after 24-36 hours.
However, the possibility still exists for the system to reach
hurricane status before or while it moves through the Cape Verde
Islands in 36-48 hours. For this reason, the Meteorological
Service of the Cape Verde Islands has issued a Hurricane Watch and a
Tropical Storm Warning for all of the Cape Verdes.  The official
intensity forecast is basically a blend of the SHIPS and LGEM
models.

FORECAST POSITIONS AND MAX WINDS

INIT  30/0530Z 12.1N  18.4W   30 KT  35 MPH
 12H  30/1200Z 12.7N  19.5W   35 KT  40 MPH
 24H  31/0000Z 13.9N  21.2W   45 KT  50 MPH
 36H  31/1200Z 15.3N  23.1W   55 KT  65 MPH
 48H  01/0000Z 16.6N  24.9W   60 KT  70 MPH
 72H  02/0000Z 18.3N  29.0W   60 KT  70 MPH
 96H  03/0000Z 18.9N  32.9W   55 KT  65 MPH
120H  04/0000Z 19.3N  36.8W   50 KT  60 MPH

$$
Forecaster Stewart

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