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Tropical Depression FIFTEEN-E


Tropical Depression Fifteen-E Discussion Number  13
NWS National Hurricane Center Miami FL       EP152017
200 PM PDT Thu Sep 14 2017

Visible satellite imagery shows that the depression is still poorly
organized.  The circulation is highly elongated, and the associated
deep convection is not well organized due to moderate easterly
shear.  The initial wind speed remains 30 kt, and leans toward the
lower Dvorak T-numbers provided by SAB given the poor satellite
presentation.  The vertical shear over the system is expected to
decrease within the next day or two, which should provide an
opportunity for the system to strengthen.  Both the statistical
guidance and the global models predict modest intensification over
the weekend, and the NHC forecast calls for the system to become a
tropical storm in 36 to 48 h, with some additional strengthening
through day 3. After that time, drier air and increasing shear is
likely to cause some weakening by the end of the forecast period.

The initial motion estimate is 280/4 kt.  The depression is
forecast to move generally westward at a slower-than-climatological
rate during the next couple of days while it is situated within
an area of weak steering flow.  Later in the period, a mid-level
trough that is expected to deepen well southwest of southern
California should steer the depression slowly poleward by early next
week.  However, there is increasing spread in the track guidance
at days 4 and 5, and there is lower confidence in the track
forecast at those times.  The NHC track forecast is once again in
best agreement with the HFIP corrected consensus model.


INIT  14/2100Z 15.6N 123.3W   30 KT  35 MPH
 12H  15/0600Z 15.9N 124.1W   30 KT  35 MPH
 24H  15/1800Z 15.9N 124.9W   30 KT  35 MPH
 36H  16/0600Z 15.7N 125.4W   35 KT  40 MPH
 48H  16/1800Z 15.6N 125.9W   40 KT  45 MPH
 72H  17/1800Z 16.0N 125.9W   45 KT  50 MPH
 96H  18/1800Z 16.7N 125.7W   45 KT  50 MPH
120H  19/1800Z 17.3N 126.0W   40 KT  45 MPH

Forecaster Brown