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Tropical Depression FIFTEEN-E


Tropical Depression Fifteen-E Discussion Number   3
NWS National Hurricane Center Miami FL       EP152017
200 AM PDT Tue Sep 12 2017

Shortwave and BD-curve infrared imagery earlier showed a deep
convective burst with -70C cold tops near the surface center.  That
convective mass has since been displaced about 90 miles west of the
exposed center and has warmed and diminished.  Therefore, the
initial intensity is held at 25 kt and agrees with the Dvorak
intensity estimates from SAB and TAFB.  The intensity forecast has
become a bit problematic.  Earlier SHIPS model runs indicated that
the shear would either persist or increase.  The latest run,
however, reveals the shear decreasing considerably after 48 hours.
On the other hand, the GFS, ECMWF, and the LGEM intensity guidance
all show the depression gradually weakening and becoming a remnant
low in 5 days or less, while the UKMET strengthens the cyclone to a
tropical storm around day 3.  A third scenario is indicated in the
HFIP Corrected Consensus (HCCA) technique, which is similar to the
GFS, ECMWF and the LGEM, but shows dissipation in less than 48
hours. The NHC forecast reflects some increase in intensity at the
24 hour period, but after that time, it shows weakening to a remnant
low in 3 days, out of respect for the GFS and ECMWF global models,
the LGEM, and the HFIP Corrected Consensus (HCCA) technique.

The motion is estimated to be westward, or 260/13 kt.  A low- to
mid-level subtropical ridge extending over the eastern Pacific from
the Baja California peninsula is forecast to build slightly
southwestward later today influencing the depression to turn
west-southwestward. At the 36 hour period, the cyclone should
gradually turn back toward the west followed by a northwestward
motion around 72 hours in response to an increasing weakness in the
ridge along 123W.  Around day 4, the depression is forecast to
turn back toward the west within the low-level trade wind flow.
The official forecast is slightly south of the previous forecast
and is in the middle of the ECMWF and HCCA solutions.


INIT  12/0900Z 15.8N 115.1W   25 KT  30 MPH
 12H  12/1800Z 15.5N 116.9W   25 KT  30 MPH
 24H  13/0600Z 15.1N 118.8W   30 KT  35 MPH
 36H  13/1800Z 15.1N 120.4W   30 KT  35 MPH
 48H  14/0600Z 15.3N 121.6W   25 KT  30 MPH
 72H  15/0600Z 15.9N 123.3W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  16/0600Z 15.9N 125.1W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  17/0600Z...DISSIPATED

Forecaster Roberts