686 
 WTPA45 PHFO 091444
 TCDCP5
 
 HURRICANE HILDA DISCUSSION NUMBER  15
 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP102015
 500 AM HST SUN AUG 09 2015
  
 AFTER A SEVERAL HOUR PERIOD WHERE THE CONVECTION SURROUNDING THE 
 CENTER OF HILDA WARMED AND SHRANK...COLD CLOUD TOPS HAVE RECENTLY 
 INCREASED IN AREA AND NOW NEARLY ENCIRCLE THE CENTER...WITH A 
 RAGGED CLOUD-FILLED EYE READILY APPARENT IN INFRARED IMAGERY. A 
 BLEND OF SUBJECTIVE DVORAK INTENSITY ESTIMATES FROM PHFO/SAB/PGTW 
 YIELDS DATA-T NUMBERS NEAR 5.0/90 KT AND CURRENT INTENSITY /CI/ 
 VALUES NEAR 5.5/102 KT...WHILE ADT YIELDS VALUES NEAR 5.5. BASED ON 
 THIS DATA...THE INITIAL INTENSITY FOR THIS ADVISORY HAS BEEN SET AT 
 100 KT. A WELL-PLACED 0717Z ASCAT PASS CONFIRMED WHAT WAS FAIRLY 
 OBVIOUS FROM SATELLITE...THAT HILDA IS A SMALL SYSTEM...AND THIS 
 DATA LED TO A REDUCTION IN THE TROPICAL STORM FORCE WIND RADII. U.S. 
 AIR FORCE HURRICANE HUNTERS ARE SCHEDULED TO BEGIN FLYING MISSIONS 
 INTO HILDA THIS EVENING...AND WILL PROVIDE INCREASED INSIGHT INTO 
 HILDA/S STRUCTURE.
 
 HILDA CONTINUES TO MOVE STEADILY TOWARD THE WEST-NORTHWEST THIS
 MORNING...WITH AN INITIAL MOTION VECTOR OF 290/11 KT. THE HURRICANE  
 IS BEING STEERED BY A MID- AND UPPER-LEVEL HIGH CENTERED FAR TO
 THE NORTHEAST...AND AN ASSOCIATED RIDGE THAT EXTENDS WESTWARD FROM
 THE HIGH. LATER TODAY AND TONIGHT HILDA WILL REACH THE WESTERN
 TERMINUS OF THE RIDGE...AND A TURN TOWARD THE NORTHWEST WILL ENSUE.
 A SIGNIFICANT DECREASE IN FORWARD SPEED IS EXPECTED BY MONDAY AS
 STEERING CURRENTS BECOME QUITE WEAK...WITH FORWARD MOTION REDUCED TO
 A CRAWL ON DAYS 3 AND 4 AS HILDA APPROACHES HAWAII FROM THE 
 SOUTHEAST. A MUCH WEAKER HILDA IS FORECAST TO MAKE A TURN TOWARD THE 
 WEST-NORTHWEST WITH SOME INCREASE IN FORWARD SPEED AT THE END OF THE 
 FORECAST PERIOD. THE OFFICIAL TRACK FORECAST HAS BEEN NUDGED 
 WESTWARD THROUGH DAY 3...CLOSELY FOLLOWING THE TVCN CONSENSUS...AND 
 SHIFTED MORE SIGNIFICANTLY TOWARD THE SOUTHWEST ON DAYS 4 AND 5... 
 INFLUENCED BY 06Z GFS/00Z ECMWF GUIDANCE.
 
 AS HILDA SLOWLY ROUNDS THE RIDGE AND GAINS LATITUDE...IT WILL
 ENCOUNTER INCREASING WESTERLY SHEAR ASSOCIATED WITH THE SUBTROPICAL
 JET STREAM...WHICH IS FORECAST TO BE ENHANCED AS A CLOSED LOW ALOFT
 TAKES SHAPE NORTH OF HAWAII. THIS INCREASE IN VERTICAL SHEAR WILL
 PLACE HILDA IN AN ENVIRONMENT WHICH IS CONDUCIVE FOR WEAKENING...
 GRADUAL AT FIRST...AND MORE PRONOUNCED TOWARD THE END OF THE
 FORECAST PERIOD AS SHEAR VALUES APPROACH 40 KT. IN THE MEANTIME...
 LITTLE CHANGE IN INTENSITY IS FORECAST TODAY...WITH STEADY WEAKENING 
 ANTICIPATED THEREAFTER. THE INTENSITY FORECAST FOLLOWS THE IVCN 
 CONSENSUS...BUT REMAINS HIGHER THAN SHIPS GUIDANCE...WHICH IS 
 THOUGHT TO BE TOO AGGRESSIVE IN DISSIPATING THE CYCLONE...WHICH IT 
 DOES BY DAY 4.
  
 
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  09/1500Z 14.7N 146.7W  100 KT 115 MPH
  12H  10/0000Z 15.4N 148.0W   95 KT 110 MPH
  24H  10/1200Z 16.4N 149.4W   90 KT 105 MPH
  36H  11/0000Z 17.3N 150.2W   75 KT  85 MPH
  48H  11/1200Z 18.0N 150.8W   60 KT  70 MPH
  72H  12/1200Z 19.0N 151.7W   45 KT  50 MPH
  96H  13/1200Z 19.5N 153.0W   35 KT  40 MPH
 120H  14/1200Z 20.0N 155.0W   30 KT  35 MPH
  
 $$
 
 FORECASTER BIRCHARD