WDPN32 PGTW 220300
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 18W WARNING NR 14//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TYPHOON (TY) 18W (HAGUPIT) HAS RAPIDLY INTENSIFIED OVER
THE PAST 12 HOURS WHILE TURNING INCREASINGLY WESTWARD UNDER THE
STEERING INFLUENCE OF A BUILDING SUBTROPICAL RIDGE TO THE NORTH.
POLEWARD OUTFLOW HAS INCREASED AHEAD OF A MID-LATITUDE TROUGH 
TO THE NORTHEAST WHILE VERTICAL WIND SHEAR HAS DECREASED WITH
THE DEVELOPMENT OF AN ENHANCED ANTICYCLONIC OUTFLOW LAYER OVER
THE TYPHOON. 
   B. THE CURRENT POSITION IS BASED ON SATELLITE FIXES FROM
PGTW AND RJTD, SEVERAL RECENT MICROWAVE SATELLITE PASSES, AND
RADAR FIXES FROM TAIWAN. THE CURRENT INTENSITY OF 85 KNOTS IS
CONSISTENT WITH DVORAK T-NUMBERS OF 4.5 FROM PGTW AND 5.0 FROM
RJTD. ANALYSIS OF RECENT DOTSTAR DROPSONDE DATA FROM AROUND THE
STORM CIRCULATION LEND HIGH CONFIDENCE TO THE WIND FIELD DEPICT-
ED IN THE CURRENT WARNING. A RAGGED AND FAIRLY BROAD EYE IS NOW
EVIDENT IN MULTISPECTRAL SATELLITE IMAGERY. A RATHER SYMMETRIC
CONVECTIVE STRUCTURE SURROUNDS THIS EYE. THE DEEPEST CONVECTION
IS LOCATED ON THE SOUTHERN PERIPHERY OF THE TYPHOON, WHERE THE
LOW LEVEL CIRCULATION CENTER HAS BEGUN TO INTERACT WITH THE
HIGH TERRAIN OF NORTHERN LUZON.
3. FORECAST REASONING
   A. THE FORECAST TRACK HAS BEEN NUDGED SLIGHLTY EQUATORWARD
BASED ON ANALYSIS OF THE ANTICIPATED STEERING FLOW PATTERN.
HOWEVER, THERE HAVE BEEN NO MAJOR CHANGES IN THE OVERALL
FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING
MESSAGE.
   B. TY 18W WILL CONTINUE TO TRACK GENERALLY WEST-NORTHWEST-
WARD OVER THE NEXT 72 HOURS UNDER THE STEERING INFLUENCE OF A
STRONG AND CONTINUOUS SUBTROPICAL RIDGE TO THE NORTH. VERTICAL
WIND SHEAR SHOULD REMAIN LOW AND POLEWARD OUTFLOW STRONG OVER
THROUGH TAU 24, ALLOWING TY 18W TO INTENSIFY SLOWLY DESPITE
SOME DISRUPTION OF THE CIRCULATION THROUGH INTERACTION WITH THE
ISLAND OF LUZON TO THE SOUTH. AFTER TAU 24, TY 18W WILL MOVE
EQUATORWARD OF A SYNTOPIC SCALE, UPPER-LEVEL ANTICYCLONE
CENTER. THE PERIPHERAL FLOW ASSOCIATED WITH THIS ANTICYCLONE
TO THE NORTH WILL INTRODUCE INCREASING VERTICAL WIND SHEAR AND
BEGIN TO DISRUPT POLEWARD OUTFLOW. THUS, THE CURRENT FORECAST
ANTICIPATES A WEAKENING TREND BEGINNING AROUND OR JUST AFTER
TAU 24 AND CONTINUING THROUGH LANDFALL JUST AFTER TAU 48.
AFTER MAKING LANDFALL, THE TYPHOON WILL WEAKEN CONSIDERABLY.
THE CURRENT FORECAST IS IN GOOD AGREEMENT WITH THE CLOSELY-
PACKED NUMERICAL MODEL GUIDANCE. HOWEVER, THE UKMET, JGSM,
AND ECMWF GUIDANCE SUGGEST THAT THE TYPHOON MAY FOLLOW A TRACK
SLIGHTLY FARTHER SOUTH, KEEPING THE CIRCULATION OVER WATER FOR
A LONGER PERIOD. IN THIS CASE, THE INTENSITIES DEPICTED IN THE
CURRENT FORECAST MAY BE TOO LOW. HOWEVER, UNFAVORABLE SYNOPTIC
INFLUENCES AND ALMOST CERTAIN LAND INTERACTION WILL STILL
PRODUCE CONSIDERABLE WEAKENING BETWEEN TAU 48 AND TAU 72 EVEN
IF THE SYSTEM SKIRTS THE CHINESE COAST AND DOES NOT TRACK
FULLY INLAND.
   C. UNDER THE CURRENT TRACK SCENARIO, TY 18W WILL CONTINUE
DISSIPATE BELOW THE WARNING THRESHOLD INTENSITY OF 25 KNOTS
BY TAU 96 WHILE TRACKING GENERALLY WESTWARD OVER LAND.
FORECAST TEAM: ALPHA//
NNNN