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Tropical Depression Nine-E Forecast Discussion


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000
WTPZ44 KNHC 220833
TCDEP4

Tropical Depression Nine-E Discussion Number   4
NWS National Hurricane Center Miami FL       EP092017
400 AM CDT Sat Jul 22 2017

The satellite appearance of the depression hasn't changed much
during the past 6 hours, and the intensity remains 30 kt based on
an average of Dvorak estimates from TAFB, SAB, and the UW-CIMSS
ADT.  Most of the convection is still removed from the center and
limited to the western half of the circulation.  That said, the
intensity forecast thinking hasn't changed, and the environment is
still expected to support strengthening throughout the forecast
period.  Given the current structure of the storm, significant
intensification doesn't seem imminent.  However, looking at the
medium-term, the SHIPS-RII probability of an increase of 65 kt in 72
hours is up to 44 percent.  The new intensity forecast is a little
lower than the previous forecast for the first 48 h, but similar
after that. The forecast remains above all of the guidance for the
first two days, and near the SHIPS model after that.

The initial motion is 285/11 kt.  A mid-level ridge extending from
the Gulf of Mexico to western Mexico is the primary steering
feature for next few days, and the models are in good agreement on
a steady northwestward track beginning later today.  All of the
global models depict the ridge strengthening after about 72 h, but
the extent to which the cyclone responds by turning toward the west
varies somewhat.  In the models with a stronger vortex, most notably
the GFS, a weak upper-level low prevents the storm from turning too
sharply toward the west.  A weaker modeled storm, as depicted in the
UKMET and HWRF would turn almost due west.  Overall, the guidance
has shifted a little to the west for this advisory, so the forecast
has been nudged in that direction.  It now lies on the right side of
the envelope, favoring the stronger solution of the GFS.

FORECAST POSITIONS AND MAX WINDS

INIT  22/0900Z  9.6N  96.6W   30 KT  35 MPH
 12H  22/1800Z 10.1N  98.2W   35 KT  40 MPH
 24H  23/0600Z 11.1N 100.1W   45 KT  50 MPH
 36H  23/1800Z 12.1N 101.8W   55 KT  65 MPH
 48H  24/0600Z 13.2N 103.4W   65 KT  75 MPH
 72H  25/0600Z 15.1N 106.5W   85 KT 100 MPH
 96H  26/0600Z 16.8N 109.9W   90 KT 105 MPH
120H  27/0600Z 18.0N 113.5W   95 KT 110 MPH

$$
Forecaster Zelinsky