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TROPICAL DEPRESSION TEN DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
1100 AM AST FRI SEP 18 2015

Satellite data indicate that the area of low pressure over the
tropical eastern Atlantic has acquired sufficient organization to be
classified as a tropical depression.  The low-level center appears
embedded beneath a relatively small cluster of deep convection, but
convective banding is also increasing to the west and north.  The
initial intensity is set at 25 kt based on Dvorak estimates from
TAFB and SAB and recent ASCAT data.

The depression is located near the southwestern edge of a mid-level
anticyclone, giving the cyclone an initial motion of 285/8 kt.  The
anticyclone is expected to move westward in tandem with the
depression over the next couple of days, keeping it on a general
west-northwestward track for much of the forecast period.  By days 4
and 5, however, there is significant uncertainty in the track
forecast.  The GFS and GFDL show the cyclone feeling the influence
of an amplifying deep-layer trough over the eastern Atlantic, which
turns the depression northward.  The ECMWF and UKMET, on the other
hand, keep the ridge as the dominant influence and continue a
west-northwestward motion.  Due to the large spread in the guidance,
the official forecast shows the cyclone slowing down considerably by
days 4 and 5, and is a little west of the model consensus aids at
those times.

The environment looks conducive for at least gradual strengthening
during the forecast period.  Sea surface temperatures are warm,
vertical shear should remain generally low, and environmental
moisture patterns appear favorable for at least the next two days.
Beyond 48 hours, most of the global models show the cyclone
threading the needle beneath a narrow upper-level ridge, with
mid-level dry air possibly getting into the western part of the
cyclone's circulation.  This pattern makes the intensity forecast
complicated because hostile upper-level winds won't be too far away,
and the ultimate strength of the cyclone will depend heavily on its
eventual track.  For now, the NHC official forecast shows only
gradual strengthening through day 4, more or less in line with the
SHIPS and LGEM guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  18/1500Z 13.1N  36.7W   25 KT  30 MPH
 12H  19/0000Z 13.4N  37.6W   30 KT  35 MPH
 24H  19/1200Z 14.2N  39.0W   30 KT  35 MPH
 36H  20/0000Z 15.2N  40.8W   35 KT  40 MPH
 48H  20/1200Z 16.4N  43.0W   40 KT  45 MPH
 72H  21/1200Z 18.3N  46.4W   45 KT  50 MPH
 96H  22/1200Z 19.5N  48.0W   50 KT  60 MPH
120H  23/1200Z 20.0N  49.0W   50 KT  60 MPH

$$
Forecaster Berg

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