WDPN32 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (CHANTHU) WARNING NR 028//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.1N 123.6E
   INITIAL INTENSITY: 85 KTS
   GEOGRAPHIC REFERENCE: 272 NM NORTHWEST OF KADENA AB
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TY 19W HAS CONTINUED TO WEAKEN STEADILY AS IT TRACKS POLEWARD ALONG
THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. ANIMATED ENHANCED
INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT, SHRINKING CORE
SURROUNDING A CLOUD-FILLED EYE WITH EXTENSIVE SPIRAL BANDING AROUND
THE PERIPHERY. A 122246Z SSMIS 91GHZ IMAGE INDICATES A BREAK IN THE
EYEWALL OVER THE WEST QUADRANT WITH EXTENSIVE CONVECTIVE BANDING 
WRAPPING BROADLY AROUND THE COMPACT CORE. UPPER-LEVEL ANALYSIS 
REVEALS MODERATE SOUTHERLY VERTICAL WIND SHEAR OFFSET BY ROBUST 
POLEWARD OUTFLOW. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON THE EIR IMAGERY. THE INITIAL INTENSITY OF 85 KTS 
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE PGTW AND KNES DVORAK 
ESTIMATES AND THE CIMSS ADT ESTIMATE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA (122332Z ASCAT-A) 

CURRENT STEERING MECHANISM: DEEP-LAYERED, NORTH-SOUTH ORIENTED
SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   RJTD: T5.5 - 102 KTS
   KNES: T5.0 - 90 KTS
   CIMSS ADT: 74 KTS AT 122340Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

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: TY 19W WILL TRACK POLEWARD ALONG THE WESTERN
PERIPHERY OF THE STR THROUGH TAU 24. THE SYSTEM SHOULD STEADILY
WEAKEN UNDER THE PERSISTENT SOUTHERLY VWS. AFTER TAU 36, TY 19W IS
EXPECTED TO SLOW EAST OF SHANGHAI AND POSSIBLY BECOME QUASI-
STATIONARY THROUGH TAU 48 AS THE SYSTEM ENCOUNTERS COMPETING
STEERING BETWEEN THE PRIMARY STR TO THE EAST AND A WEAK STR TO THE
WEST. AFTER TAU 48, THE WESTERLIES WILL STRENGTHEN WITH AN
APPROACHING SHORTWAVE TROUGH DIGGING OVER EASTERN CHINA, WHICH WILL
WEAKEN THE WESTERN STR AND ALLOW TY 19W TO ACCELERATE EAST-
NORTHEASTWARD. THE SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION
(ETT) BY TAU 96 AS IT INTERACTS WITH THE BAROCLINIC ZONE OVER THE
KOREAN PENINSULA. AS THE SYSTEM APPROACHES SOUTH KOREA, IT WILL
ACCELERATE WITHIN THE STRONG WESTERLY FLOW AND WILL WEAKEN TO ABOUT
40 KNOTS DUE TO STRONG VWS (30-40 KNOTS). BY TAU 120, TY 19W WILL
COMPLETE ETT AS IT GAINS FRONTAL CHARACTERISTICS AND NEARS THE
UPPER-LEVEL JET. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE DEPICTS A LARGE DEGREE
OF UNCERTAINTY AFTER TAU 12 WITH THE MODELS STRUGGLING WITH THE
TRACK FORECAST WITHIN A WEAK, COMPETING STEERING ENVIRONMENT. SOME
MODEL SOLUTIONS TRACK THE SYSTEM NEAR SHANGHAI WHILE THE BULK
REVEAL A QUASI-STATIONARY MOTION OVER WATER BEFORE RECURVING THE
SYSTEM EAST-NORTHEASTWARD. THE JTWC FORECAST TRACK IS POSITIONED
CLOSE TO THE JTWC MULTI-MODEL CONSENSUS (CONW) AND INDICATES VERY
SLOW TRACK SPEEDS FROM TAU 12 TO TAU 48. THERE IS ALSO A HIGH
DEGREE OF UNCERTAINTY IN THE INTENSITY FORECAST DUE TO THE
INCREASINGLY MARGINAL ENVIRONMENT AND INTERACTION WITH LAND. AFTER
TAU 72, THERE IS INCREASING UNCERTAINTY DUE TO THE ETT, LAND
INTERACTION AND INCREASING TRACK SPEEDS. OVERALL, THERE IS MEDIUM 
CONFIDENCE IN THE JTWC TRACK AND INTENSITY FORECAST. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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