WDPN32 PGTW 091500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 28W (HALONG) WARNING NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 33.9N 146.7E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 356 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: EASTWARD AT 26 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS WHAT
APPEARS TO BE A WELL-ORGANIZED TYPHOON, WITH A WELL-DEFINED CENTER,
AT LEAST IN THE UPPER-LEVELS. HOWEVER, UNDER THE HOOD THE STORY IS
DIFFERENT. A VERY TIMELY 091140Z ASCAT-C BULLSEYE REVEALED THAT A
SIGNIFICANT AMOUNT OF VORTEX DECOUPLING IS ALREADY UNDERWAY, WITH
THE LOW LEVEL CIRCULATION CENTER (LLCC) DISPLACED ROUGHLY 34NM TO
THE SOUTHWEST OF THE CENTER DERIVED FROM THE EIR IMAGERY AND AGENCY
FIX POSITIONS. LOW RESOLUTION AMSU-B 89GHZ MICROWAVE IMAGERY FROM
091102Z SHOWS A VERY WEAK AND SHALLOW INNER-CORE OF TY 28W AND A
BROAD OUTER BAND OF MODERATE CONVECTION DRAPED ACROSS THE NORTHERN
PERIPHERY OF THE CIRCULATION AND WHAT IS LIKELY A DEVELOPING COLD
FRONT WELL OUT IN FRONT OF THE SYSTEM, CURLING DOWN TO THE
SOUTHWEST. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE ASCAT DATA. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON A BLEND OF THE SUBJECTIVE AND OBJECTIVE
INTENSITY ESTIMATES NOTED BELOW. ENVIRONMENTAL CONDITIONS ARE
RAPIDLY DETERIORATING, WITH DEEP-LAYER SHEAR NOW ESTIMATED TO BE 40
KNOTS FROM THE SOUTHWEST, SSTS ARE MARGINAL AT BEST, AND DRY AIR IS
BEGINNING TO ENCROACH FROM THE WEST. THE ONLY FAVORABLE ASPECT FOR
THE MOMENT IS THE EXTREMELY STRONG POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.0 - 90 KTS
   CIMSS ADT: 90 KTS AT 091130Z
   CIMSS AIDT: 86 KTS AT 091130Z
   CIMSS D-PRINT: 72 KTS AT 091130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 30+ KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: RAPID VORTEX DECOUPLING. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TYPHOON (TY) 28W (HALONG) CONTINUES TO
ACCELERATE AS IT RACES OFF TO THE EAST-NORTHEAST ALONG THE NORTHERN
SIDE OF THE DEEP STR TO THE SOUTHEAST. THE RIDGE IS EXPECTED TO
SLIDE WESTWARD OVER THE COURSE OF THE FORECAST PERIOD, ENDING UP IN
A POSITION SOUTH OF TOKYO, WITH A SECONDARY RIDGE CENTER DEVELOPING
NEAR THE DATELINE BY THE END OF THE FORECAST. TY 28W WILL TRACK
EAST-NORTHEASTWARD ALONG THE NORTH SIDE OF RIDGE THROUGH TAU 24,
THEN TURN NORTHEASTWARD AS IT COMES UNDER THE STEERING INFLUENCE OF
THE SECONDARY RIDGE CENTER. THE SYSTEM IS ALREADY STARTING TO
DECOUPLE, AHEAD OF WHEN THE HAFS-A AND COAMPS-TC MODELS THOUGHT
THIS PROCESS WOULD COMMENCE. NOW THAT IT HAS STARTED, THE
DECOUPLING PROCESS SHOULD BE RELATIVELY QUICK. DRY AIR WILL QUICKLY
MOVE IN FROM THE WEST AND SMOTHER THE LOWER-LEVEL VORTEX, WHILE
SHEAR CONTINUES TO INCREASE AND THE SYSTEM LOSES ITS ENERGY SOURCE
AS IT MOVES OVER COOLER WATERS. SIMULTANEOUSLY, TY 28W WILL BEGIN
EXTRATROPICAL TRANSITION (ETT) AS IT BEGINS TO INTERACT WITH THE
MID-LATITUDE WESTERLIES AND BEGINS FRONTOGENESIS. COMPLETION OF ETT
IS EXPECTED BETWEEN 101800Z AND 110000Z AS THE LOW-LEVEL VORTEX
MOVES UNDER THE JET MAX BEGINS TO OCCLUDE. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN STRONG
AGREEMENT THROUGH THE FORECAST PERIOD, WITH LITTLE IN THE WAY OF
EITHER CROSS- OR ALONG-TRACK SPREAD, LENDING HIGH CONFIDENCE TO THE
JTWC FORECAST. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, THOUGH
THE JTWC FORECAST IS PLACED ON THE UPPER EDGE OF THE GUIDANCE AS
THE SYSTEM WILL TAKE TIME TO SPIN DOWN AND WILL EVENTUALLY
REINTENSIFY DUE TO STRONG BAROCLINIC FORCING AFTER THE END OF THE
FORECAST PERIOD. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM//
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