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Tropical Storm Hilary Discussion Number   8
NWS National Hurricane Center Miami FL       EP092017
400 AM CDT Sun Jul 23 2017

The cloud pattern of Hilary is gradually becoming better organized,
with some convective banding features beginning to develop.  The
upper-level outflow is well defined over all but the southeastern
semicircle of the circulation.  Dvorak T-numbers from TAFB and SAB
remain at 2.5 so the current intensity is held at 35 kt.  This is
also consistent with ASCAT data from a few hours ago.  The
atmospheric and oceanic environment should be quite favorable for
intensification during the next few days.  The SHIPS guidance
indicates that the vertical shear should remain below 10 kt
throughout the forecast period, and the global models show a large
upper-level anticyclone over Hilary through 4-5 days.  Late in the
period Hilary is expected to move over cooler SSTs, and this should
halt the intensification process.  The official intensity forecast
shows the system approaching major hurricane status in 72 hours
and some of the guidance, including the corrected consensus models,
suggest that this could be conservative.

Overnight microwave data indicate a bit of a jump to the
west-northwest, perhaps as a result of reformation of the center as
opposed to large-scale motion.  The initial motion estimate is
300/13 kt.  A large mid-level anticyclone centered over the
southwestern United States or northwestern Mexico should maintain
the west-northwestward heading throughout the forecast period.  The
track model guidance is in agreement on a decrease in forward speed,
and the official forecast shows this as well.  Later in the period,
there is a possibility of some binary interaction with Tropical
Storm Irwin currently located some 800 n mi to the west. This, along
with a substantial spread in the track models at 4-5 days, adds some
uncertainty to the forecast.  In any event, the official track
forecast is not far from the latest model consensus, and keeps the
system well offshore of the coast of Mexico.

FORECAST POSITIONS AND MAX WINDS

INIT  23/0900Z 12.5N 101.6W   35 KT  40 MPH
 12H  23/1800Z 13.1N 102.8W   45 KT  50 MPH
 24H  24/0600Z 13.9N 104.3W   55 KT  65 MPH
 36H  24/1800Z 14.7N 105.8W   65 KT  75 MPH
 48H  25/0600Z 15.5N 107.3W   80 KT  90 MPH
 72H  26/0600Z 17.0N 111.0W   95 KT 110 MPH
 96H  27/0600Z 18.0N 115.0W   95 KT 110 MPH
120H  28/0600Z 19.0N 118.5W   85 KT 100 MPH

$$
Forecaster Pasch

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