WTPZ44 KNHC 280254 RRA

TCDEP4



TROPICAL STORM HILARY DISCUSSION NUMBER  27

NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092017

800 PM PDT THU JUL 27 2017



DEEP CONVECTION ASSOCIATED WITH HILARY HAS BEEN DECREASING DURING

THE LAST SEVERAL HOURS, AND THE CONVECTIVE PATTERN IS NOW LIMITED TO

A RAGGED CENTRAL DENSE OVERCAST.  THIS LOSS OF CONVECTION APPEARS TO

BE ASSOCIATED WITH DRY AIR THAT HAS WRAPPED INTO THE CIRCULATION, AS

EVIDENT IN MICROWAVE DATA.  AN AVERAGE OF THE LATEST FINAL T- AND

CI-NUMBERS FROM TAFB/SAB, ALONG WITH ADT VALUES FROM CIMSS AT THE

UNIVERSITY OF WISCONSIN, SUPPORT LOWERING THE INITIAL INTENSITY TO

60 KT, MAKING HILARY A TROPICAL STORM.



HILARY STILL HAS ANOTHER 18-24 HOURS OVER WARM WATER, AND THE

REGIONAL HURRICANE MODELS RESPOND TO THIS BY SHOWING HILARY

RESTRENGTHENING DURING THAT TIME.  GIVEN THE OBSERVED WEAKENING

TREND OVER THE PAST DAY OR SO AND HILARY'S CURRENT STRUGGLE WITH DRY

AIR, THE NHC INTENSITY FORECAST LIES AT THE LOW END OF THE GUIDANCE

DURING THAT TIME FRAME, AND CALLS FOR THE STORM TO REMAIN STEADY IN

INTENSITY.  AFTER 24 HOURS, HILARY IS EXPECTED TO CROSS THE 26-DEG C

ISOTHERM AND IT WILL BE MOVING OVER EVEN COOLER WATERS AND INTO A

DRIER AIR MASS DURING THE NEXT FEW DAYS.  THESE UNFAVORABLE

CONDITIONS SHOULD CAUSE WEAKENING, AND HILARY IS FORECAST TO BECOME

A POST-TROPICAL CYCLONE IN ABOUT 4 DAYS.  THE NHC INTENSITY FORECAST

IS SIMILAR TO THE PREVIOUS ONE, AND IT LIES FAIRLY CLOSE TO THE

SHIPS AND LGEM MODELS.



THE TROPICAL STORM IS MOVING WEST-NORTHWESTWARD AT 7 KT ON THE SOUTH

SIDE OF A MID-LEVEL RIDGE.  THIS MOTION WITH A SLIGHT INCREASE IN

FORWARD SPEED IS EXPECTED DURING THE NEXT COUPLE OF DAYS AS THE