000
WTPZ44 KNHC 252037
TCDEP4
 
HURRICANE HILARY DISCUSSION NUMBER  19
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP092011
200 PM PDT SUN SEP 25 2011
 
SINCE THE PREVIOUS ADVISORY...HILARY HAS MAINTAINED A PRONOUNCED EYE
FEATURE IN BOTH VISIBLE AND INFRARED SATELLITE IMAGERY...WHICH HAS
BECOME EVEN MORE DISTINCT AND WARMER DURING THE PAST COUPLE OF
HOURS. SATELLITE INTENSITY ESTIMATES ARE T6.0/115 KT FROM TAFB AND
T5.0/90 KT FROM SAB. BASED ON THE RECENT WARMING AND CLEARING OUT
OF THE EYE...THE INITIAL INTENSITY WILL REMAIN A LITTLE ABOVE THE
AVERAGE OF THESE INTENSITY ESTIMATES AND AS A MAJOR HURRICANE.

HILARY HAS BEEN MOVING IN A STEADY WESTWARD MOTION OR 270/9 KT FOR
THE PAST 6 HOURS. THE HURRICANE IS MOVING AROUND THE SOUTHERN
PERIPHERY OF A STRONG DEEP-LAYER RIDGE EXTENDING WESTWARD TO THE
NORTH OF THE CYCLONE. THIS STEERING FLOW PATTERN SHOULD RESULT IN A
WESTWARD MOTION FOR THE NEXT 24 HOURS OR SO...FOLLOWED BY A TURN TO
THE WEST-NORTHWEST AFTER THAT. BY 72 HOURS...A MID- TO UPPER-LEVEL
LOW...INDICATED IN WATER VAPOR IMAGERY NEAR 23N 134W...IS FORECAST
TO MOVE EASTWARD AND ERODE THE WESTERN PORTION OF THE RIDGE AND
ALLOW HILARY TO MOVE SLOWLY NORTHWARD. BY DAYS 4 AND 5...HILARY IS
FORECAST TO UNDERGO SOME BINARY INTERACTION WITH THE UPPER-LOW AND
MOVE NORTHWARD OR EVEN NORTH-NORTHWESTWARD AT A SLIGHTLY FASTER
FORWARD SPEED. THE NHC FORECAST TRACK IS A LITTLE TO THE LEFT OF
THE PREVIOUS ADVISORY TRACK...AND LIES ABOUT MIDWAY BETWEEN THE GFS
AND ECMWF MODEL FORECASTS.

HILARY IS EXPECTED TO REMAIN IN A LOW VERTICAL SHEAR REGIME AND OVER
WARM WATERS FOR THE NEXT 72 HOURS...WHICH WOULD GENERALLY FAVOR
STRENGTHENING OR AT LEAST MAINTAIN A STEADY INTENSITY.  HOWEVER...
THE MID-LEVEL MOISTURE SURROUNDING THE HURRICANE IS ALREADY FAIRLY
DRY AND IS FORECAST TO DROP BELOW 40 PERCENT HUMIDITY BY 24-36
HOURS. A 25/1511Z SSMIS MICROWAVE OVERPASS INDICATED DRY AIR
ALREADY BEGINNING TO WRAP INTO THE SOUTHERN SEMICIRCLE OF THE INNER
CORE CIRCULATION...WHICH MAY CAUSE EROSION OF THE CONVECTION AROUND
THE EYE FAIRLY SOON. AS A RESULT...GRADUAL WEAKENING IS FORECAST
FOR THE NEXT 3-4 DAYS...WITH MORE RAPID WEAKENING AFTER THAT AS
HILARY MOVES OVER WATER COLDER THAN 24C AND INTO INCREASING
SOUTHWESTERLY VERTICAL SHEAR. THE OFFICIAL INTENSITY FORECAST
FOLLOWS THE TREND OF INTENSITY CONSENSUS MODEL...ICON...THROUGH 72
HOURS AND THEN IS BELOW THE CONSENSUS MODEL AFTER THAT.

FORECAST POSITIONS AND MAX WINDS
 
INIT  25/2100Z 17.1N 110.3W  110 KT 125 MPH
 12H  26/0600Z 17.2N 111.6W  105 KT 120 MPH
 24H  26/1800Z 17.3N 113.2W  105 KT 120 MPH
 36H  27/0600Z 17.6N 114.7W  100 KT 115 MPH
 48H  27/1800Z 18.1N 115.6W   95 KT 110 MPH
 72H  28/1800Z 19.7N 116.2W   80 KT  90 MPH
 96H  29/1800Z 22.1N 115.8W   60 KT  70 MPH
120H  30/1800Z 25.0N 116.0W   40 KT  45 MPH
 
$$
FORECASTER STEWART