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Tropical Storm Hilary Forecast Discussion

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WTPZ44 KNHC 240250

Tropical Storm Hilary Discussion Number  11
NWS National Hurricane Center Miami FL       EP092017
1000 PM CDT Sun Jul 23 2017

Hilary has continued to become better organized with a curved
convective band now wrapping nearly all the way around the
low-level center, and a banding eye of about 10 n mi in diameter
evident in recent SSMI/S microwave satellite data. The intensity
estimate was 55 kt by TAFB at 0000Z, but since the overall
convective and inner-core patterns have improved during the past few
hours, the initial intensity is increased to 60 kt for this

The initial motion estimate is 300/08 kt. There is no significant
change to the previous forecast track or reasoning. Hilary is
expected to move west-northwestward along the southern periphery of
a deep-layer ridge to its north for the next several days, with a
slight increase in forward speed expected in about 48 hours or so.
The new model guidance is tightly packed around the previous
NHC advisory track through 96 h, so the new forecast track is just
an update of the previous one, and closely follows the HCCA and
TVCN models.

Given the improving inner-core structure, coupled with very low
vertical shear values and a moist unstable environment, continued
rapid intensification appears likely for the next 36-48 hours while
the small cyclone remains over SSTs greater than 28C. By 72 hours,
SSTs cool to near 27C and the upper-ocean heat content decreases to
less than 10 units, suggesting that cold upwelling will probably
begin around that time. The new intensity forecast follows the
previous advisory by showing rapid strengthening of about 15 kt
every 12 hours for the next 36 hours, followed by a slightly slower
rate of strengthening since an eyewall replacement cycle could begin
in the 36-48 h period. After that, increasing shear and cooler
water temperatures should induce gradual weakening. The official
intensity forecast is similar to the corrected-consensus model HCCA,
which brings Hilary to a 116-kt, category-4 hurricane in 48 hours.


INIT  24/0300Z 13.6N 103.5W   60 KT  70 MPH
 12H  24/1200Z 14.0N 104.5W   70 KT  80 MPH
 24H  25/0000Z 14.7N 106.0W   85 KT 100 MPH
 36H  25/1200Z 15.4N 107.6W  100 KT 115 MPH
 48H  26/0000Z 16.1N 109.5W  110 KT 125 MPH
 72H  27/0000Z 17.2N 113.4W  105 KT 120 MPH
 96H  28/0000Z 18.3N 117.1W   90 KT 105 MPH
120H  29/0000Z 19.2N 120.8W   80 KT  90 MPH

Forecaster Stewart