723 
 WTPA45 PHFO 100903
 TCDCP5
 
 HURRICANE HILDA DISCUSSION NUMBER  18
 NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI   EP102015
 1100 PM HST SUN AUG 09 2015
  
 THE FIRST RECONNAISSANCE FLIGHT INTO HILDA WAS CONDUCTED BY THE 
 U.S. 53RD WEATHER RECONNAISSANCE SQUADRON EARLIER THIS EVENING... 
 WITH ANOTHER MISSION SCHEDULED FOR MONDAY MORNING. THE AIRCRAFT DATA 
 CONFIRM THAT HILDA IS A VERY SMALL SYSTEM...AND BASED ON A BLEND OF 
 THE FLIGHT LEVEL...DROPSONDE AND SFMR WINDS...THE INITIAL INTENSITY 
 FOR THIS ADVISORY IS DETERMINED TO BE 85 KT. THE HURRICANE HUNTERS 
 NOTED THAT THE EYE WAS EVOLVING IN SHAPE AND SIZE...WITH BREAKS IN 
 THE EYE WALL APPARENT. GRADUALLY INCREASING CENTRAL PRESSURE LEADS 
 TO THE CONCLUSION THAT HILDA IS ON A WEAKENING TREND.
 
 THE TRACK AND INTENSITY FORECASTS FOR HILDA REMAIN INTRICATELY 
 LINKED AS THE CYCLONE INTERACTS WITH AN INCREASINGLY HOSTILE 
 ENVIRONMENTAL WIND PROFILE. IF HILDA WERE TO REMAIN A STRONG AND 
 DEEP SYSTEM...IT WOULD BE INFLUENCED BY STEERING FLOW THROUGH A 
 DEEPER LAYER OF THE ATMOSPHERE...WHICH WOULD RESULT IN A MORE 
 NORTHERLY TRACK. THE WEAKER AND SHALLOWER HILDA BECOMES...THE MORE 
 ITS TRACK WILL BE INFLUENCED BY THE LOW-LEVEL TRADE WIND FLOW... 
 RESULTING IN A MORE WESTERLY TRACK. THE OFFICIAL FORECAST ASSUMES A
 FAIRLY DEEP SYSTEM INITIALLY WILL BECOME INCREASINGLY SHALLOW
 THROUGH THE FORECAST PERIOD. 
 
 THE CURRENT MOTION ESTIMATE IS 300/08 KT...AS HILDA IS ROUNDING THE 
 WESTERN EDGE OF A DEEP LAYER RIDGE CENTERED TO THE DISTANT 
 EAST-NORTHEAST. HILDA WILL CONTINUE TO GAIN LATITUDE OVER THE NEXT 
 COUPLE OF DAYS AS IT GRADUALLY ROUNDS THE RIDGE. AS IT DOES SO...
 HILDA WILL BEGIN TO FEEL THE EFFECTS OF INCREASING WESTERLY WINDS
 ALOFT...ASSOCIATED WITH THE SUBTROPICAL JET STREAM THAT IS BEING 
 ENHANCED BY A LOW ALOFT CENTERED NORTH OF HAWAII. THE FORWARD 
 MOTION OF THE CYCLONE IS FORECAST TO DIMINISH SIGNIFICANTLY OVER
 THE NEXT 48 HOURS AS THE STEERING FLOW WEAKENS...AND THE LOWER AND
 UPPER LEVELS OF THE SYSTEM GRADUALLY DECOUPLE. IN THE LATER
 PERIODS...SHEAR WILL REMAIN HIGH...AND THE FORECAST ANTICIPATES THAT
 A MUCH WEAKER HILDA WILL BEGIN TO MOVE TOWARD THE WEST-NORTHWEST 
 WITH A GRADUAL INCREASE IN FORWARD SPEED. 
 
 THE OFFICIAL TRACK FORECAST IS CLOSE TO THE PREVIOUS...BUT HAS
 BEEN NUDGED TOWARD THE TVCN CONSENSUS. THE TRACK FORECAST THUS
 WAS NUDGED A LITTLE TO THE LEFT INITIALLY...AND A LITTLE TO THE
 RIGHT ON DAYS 4 AND 5...IN RESPONSE TO A SHIFT SEEN IN THE LATEST
 ECMWF GUIDANCE. THE INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS...
 AND CLOSELY FOLLOWS THE IVCN CONSENSUS. THE FORECAST ANTICIPATES 
 THAT HILDA WILL WEAKEN TO A TROPICAL STORM ON TUESDAY. 
 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INIT  10/0900Z 15.7N 149.1W   85 KT 100 MPH
  12H  10/1800Z 16.3N 150.1W   75 KT  85 MPH
  24H  11/0600Z 17.0N 151.0W   65 KT  75 MPH
  36H  11/1800Z 17.6N 151.7W   55 KT  65 MPH
  48H  12/0600Z 18.1N 152.1W   50 KT  60 MPH
  72H  13/0600Z 18.8N 153.1W   35 KT  40 MPH
  96H  14/0600Z 19.3N 155.0W   30 KT  35 MPH
 120H  15/0600Z 20.0N 158.0W   25 KT  30 MPH
  
 $$
 
 FORECASTER BIRCHARD