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Tropical Depression NINE-E Forecast Discussion

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WTPZ44 KNHC 220240

Tropical Depression Nine-E Discussion Number   3
NWS National Hurricane Center Miami FL       EP092017
1000 PM CDT Fri Jul 21 2017

Recent microwave images suggest that Tropical Depression Nine-E has
formed a small inner core with good curvature of the low cloud
lines.  However, deep convection near this feature is currently
minimal, with most of the convection well away from the center over
the northwestern quadrant.  Satellite intensity estimates are in the
25-35 kt range, and based on these and the current state of the
central convection, the initial intensity remains 30 kt.  The
cyclone has good outflow in all directions.

The initial motion is 280/12.  The depression is south of a
mid-level ridge extending from Mexico westward into the
northeastern Pacific just west of the Baja California peninsula.
This pattern should steer the cyclone generally west-northwestward
to northwestward for the next three days or so.  After that time,
the ridge is forecast to strengthen a little, which should give the
tropical cyclone a more westward motion.  The track guidance is in
good agreement with this scenario, and the new forecast track is
similar to the old forecast.  This forecast, which lies just north
of the various consensus models, keeps the core of the cyclone well
south of the coast of Mexico at this time.

The environment looks very favorable for strengthening, with the
depression forecast to be in light vertical shear and over waters
of 28-29C for at least the next 4 days.  Based on this, a period of
rapid intensification seems likely, but when this will occur is not
clear.  The intensity guidance shows generally slow strengthening
for the next 36 h, and the SHIPS Rapid Intensification Index is not
unusually high through 36 h.  However, the aforementioned inner core
suggests that rapid intensification could begin if the convection
concentrates around this feature.  Given the uncertainty, the
intensity forecast is changed little since the previous advisory,
showing the system becoming a hurricane just before 48 h and
getting to near major hurricane strength by the end of the period.
This forecast is above the guidance through 72 h, then is in good
agreement with the SHIPS model.   It is possible that the current
forecast intensities may be too high during the first 36 h and not
high enough later in the forecast.


INIT  22/0300Z  9.4N  95.7W   30 KT  35 MPH
 12H  22/1200Z  9.7N  97.3W   40 KT  45 MPH
 24H  23/0000Z 10.7N  99.3W   50 KT  60 MPH
 36H  23/1200Z 11.8N 101.0W   60 KT  70 MPH
 48H  24/0000Z 12.8N 102.5W   70 KT  80 MPH
 72H  25/0000Z 15.0N 105.5W   80 KT  90 MPH
 96H  26/0000Z 16.5N 108.5W   90 KT 105 MPH
120H  27/0000Z 18.0N 112.0W   95 KT 110 MPH

Forecaster Beven