WTPZ44 KNHC 252042 RRA

TCDEP4



HURRICANE HILARY DISCUSSION NUMBER  18

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092017

300 PM MDT TUE JUL 25 2017



HILARY CONTINUES TO HAVE A SOMEWHAT ASYMMETRIC PRESENTATION ON THE

LATEST SATELLITE IMAGERY, WITH AN EYE FEATURE IN THE NORTHWESTERN

PORTION OF THE CENTRAL DENSE OVERCAST, SUGGESTIVE OF SOME

NORTHWESTERLY SHEAR.  THE INITIAL WIND SPEED REMAINS 90 KT SINCE

THERE HAVE BEEN NO SIGNIFICANT CHANGES TO THE SATELLITE ESTIMATES.

HIGHER WIND SHEAR IS NOT FAR AWAY FROM THE HURRICANE, AS EVIDENCED

BY SOUTHWARD-MOVING CIRRUS CLOUDS MOVING TOWARD THE CENTER IN THE

NORTHERN SEMICIRCLE. THUS THE WINDOW OF TIME FOR HILARY TO INTENSIFY

MAY BE CLOSING, AND LITTLE CHANGE IN WIND SPEED IS SHOWN FOR THE

NEXT DAY OR SO. AFTERWARD, GRADUALLY COOLING SSTS, ENTRAINMENT OF

DRIER AIR, AND INTERACTION WITH HURRICANE IRWIN IS LIKELY TO CAUSE

MORE SIGNIFICANT WEAKENING.  THE NHC FORECAST IS REDUCED FROM THE

PREVIOUS ONE IN THE NEAR TERM DUE TO THE SHEAR, AND AT LONG RANGE AS

HILARY PROBABLY MOVES OVER COLD WATERS.  THIS IS NOT A PARTICULARLY

CONFIDENT FORECAST AT DAYS 4-5 DUE TO THE INTERACTION WITH IRWIN.



THE INITIAL MOTION ESTIMATE IS THE SAME AS PREVIOUS, 285/10 KT. A

MID-TROPOSPHERIC RIDGE EXTENDING WESTWARD FROM THE SOUTHWESTERN

UNITED STATES SHOULD CAUSE HILARY TO CONTINUE ON A WEST TO

WEST-NORTHWESTWARD TRACK FOR THE NEXT SEVERAL DAYS.  IN A FEW DAYS,

HOWEVER, HILARY IS LIKELY TO PASS CLOSE TO HURRICANE IRWIN.  WHILE

IRWIN WON'T AFFECT HILARY TOO MUCH, THE BULK OF THE GUIDANCE IS

SHOWING HILARY SLOWING DOWN AND TURNING SLIGHTLY LEFT AS IRWIN PULLS

ON HILARY'S CIRCULATION.  MODEL GUIDANCE HAS BECOME MORE DIVERGENT