WDPN31 PGTW 081500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (CHAN-HOM) 
WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 16W (CHAN-HOM), LOCATED APPROXIMATELY 475 NM
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT
08 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED 
(EIR) SATELLITE IMAGERY DEPICTS SPIRAL BANDS OF DEEP CONVECTION 
WRAPPING INTO A RAGGED, 30 NM DIAMETER EYE. THE INITIAL POSITION 
IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE IN THE EIR 
LOOP. THE INITIAL INTENSITY OF 80 KTS IS PLACED WITH HIGH 
CONFIDENCE AND IS HEDGED BETWEEN MULTI-AGENCY DVORAK CURRENT 
INTENSITY ESTIMATES OF T4.5 (77 KTS, PGTW, RJTD AND KNES), A CIMSS 
ADVANCED DVORAK TECHNIQUE CURRENT INTENSITY ESTIMATE OF T4.6 (80 
KTS) AND A 080947Z CIMSS SATCON INTENSITY ESTIMATE OF 81 KTS. TY 
16W IS TRACKING ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE
(STR) POSITIONED TO THE EAST AND THROUGH AN ENVIRONMENT THAT HAS
REMAINED FAVORABLE FOR DEVELOPMENT OVER THE PAST 6 HOURS WITH 
MODERATE (15-20 KTS) VERTICAL WIND SHEAR (VWS) OFFSET BY WARM 
(27-28 CELSIUS) SEA SURFACE TEMPERATURES (SST) AND ROBUST POLEWARD 
AND EQUATORWARD OUTFLOW ALOFT. THE POLEWARD OUTFLOW CONTINUES TO 
BE ENHANCED BY THE WESTERLY FLOW OF THE JET POSITIONED TO THE 
NORTH OVER JAPAN.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TY CHAN-HOM WILL CONTINUE TO TRACK GENERALLY NORTHEASTWARD
OVER THE NEXT 24 HOURS. DURING THIS TIME, THE SYSTEM WILL GRADUALLY
WEAKEN TO 65 KNOTS BY TAU 24 LARGELY DUE TO VWS THAT IS FORECAST TO
EXCEED 30 KTS BY TAU 24. AFTER THIS TIME, THE TRACK WILL BECOME 
GENERALLY EAST-NORTHEASTWARD AS THE SYSTEM TRACKS ALONG THE NORTHERN
PERIPHERY OF THE STEERING STR AND APPROACHES THE BAROCLINIC ZONE. BY
TAU 48, CONTINUED HIGH VWS COUPLED WITH COOL (23-24 CELSIUS) SST
WILL LEAD TO CONTINUED WEAKENING TO 50 KTS AS THE SYSTEM BEGINS 
EXTRATROPICAL TRANSITION. BY TAU 72, THE SYSTEM WILL BECOME FULLY
EMBEDDED IN THE AFOREMENTIONED WESTERLY FLOW ALOFT AND WILL COMPLETE
ETT, BECOMING A SIGNIFICANT (45 KTS) COLD CORE LOW. NUMERICAL MODEL
SOLUTIONS HAVE DIVERGED SIGNIFICANTLY SINCE THE LAST SET OF 
COMPUTATIONAL RUNS. THIS DIVERGENCE IS LIKELY DUE TO THE TIMING OF
A REORIENTATION OF THE STEERING RIDGE AND ITS INTERACTION WITH A
LARGE, WESTWARD PROPAGATING UPPER LEVEL LOW APPROACHING FROM THE
SOUTHEAST. THIS DYNAMIC STEERING ENVIRONMENT LEADS TO A BIFURCATION
IN MODEL SOLUTIONS. SPECIFICALLY, THE DETERMINISTIC GFS AND JGSM
GUIDANCE BRINGS THE CYCLONE CENTER SOUTHEASTWARD AFTER TAU 48
WHILE GFS ENSEMBLE, ECMWF AND UKMET MODEL GUIDANCE PROVIDE EASTWARD
AND NORTHEASTWARD TRACKS THROUGHOUT THE REMAINDER OF THE FORECAST
PERIOD. SPECIFICALLY, THERE IS A 262 NM SPREAD IN ACROSS TRACK
SOLUTIONS BY TAU 48 THAT INCREASES TO 766 NM BY TAU 72. ALL 
INTERESTS IN THE KANTO PLAIN REGION OF JAPAN SHOULD MAINTAIN
CLOSE SITUATIONAL AWARENESS OF CHANGES IN STORM MOTION AS WELL AS
THE EVOLUTION OF THE WIND FIELD GIVEN THE EXTENSIVE AMBIENT
NORTHEASTERLY FLOW AND HIGH DEGREE OF DIVERGENCE IN THE MODEL 
GUIDANCE. OVERALL THE LARGE SPREAD IN MODEL SOLUTIONS LENDS POOR
CONFIDENCE IN THE JTWC FORECAST, WHICH IS PLACED CLOSE TO THE JTWC 
MULTI-MODEL CONSENSUS.
//
NNNN