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TROPICAL DEPRESSION TEN DISCUSSION NUMBER   2
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL102015
500 PM AST FRI SEP 18 2015

The cloud pattern of the depression has continued to improve, with
well-defined convective banding wrapping around the center.  1800
UTC Dvorak estimates from TAFB and SAB support tropical storm
intensity, but since ASCAT data from earlier this morning only
showed 20 kt of wind in the inner core, the initial intensity is
only being raised to 30 kt for now.  Barring any unexpected
changes, the depression will likely be a tropical storm by this
evening.  The environment appears generally conducive for gradual
strengthening during the next few days, but the global models
show that the cyclone will be located precariously beneath a narrow
upper-level ridge, especially on days 3 through 5.  Even a slight
deviation from this pattern could put the cyclone in a higher-shear
environment and thus limit intensification, or even induce
weakening.  The NHC intensity forecast continues to show gradual
strengthening through the forecast period and is close to a
consensus of the SHIPS and LGEM models.

The initial motion is 285/7 kt, with the depression being steered
by a mid-level anticyclone to its northwest.  This anticyclone is
expected to move westward at the same pace as the depression during
the next few days, maintaining a west-northwestward motion through
48 hours.  After that time, the steering currents are forecast to
collapse near the cyclone when a deep-layer trough amplifies over
the eastern Atlantic.  As a result, the models show very slow
motion occurring by days 4 and 5, and the updated NHC track
forecast shows the cyclone becoming stationary at the end of the
forecast period.  This forecast is largely unchanged from the
previous one and is near the middle of the tightly clustered
guidance envelope.

FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z 13.4N  37.3W   30 KT  35 MPH
 12H  19/0600Z 13.9N  38.4W   35 KT  40 MPH
 24H  19/1800Z 14.9N  40.1W   40 KT  45 MPH
 36H  20/0600Z 16.1N  42.5W   45 KT  50 MPH
 48H  20/1800Z 17.2N  44.7W   50 KT  60 MPH
 72H  21/1800Z 19.5N  47.6W   50 KT  60 MPH
 96H  22/1800Z 20.5N  48.5W   55 KT  65 MPH
120H  23/1800Z 20.5N  48.5W   55 KT  65 MPH

$$
Forecaster Berg

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