WDPN31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (CHAN-HOM) WARNING NR 018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 16W (CHAN-HOM), LOCATED APPROXIMATELY 453 NM
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWARD AT 03 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY 
(MSI) DEPICTS SPIRAL BANDS OF DEEP CONVECTION WRAPPING INTO A 
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A MICROWAVE EYE 
FEATURE IN SEEN IN A 082235Z SSMIS 37GHZ IMAGE. THE INITIAL INTENSITY 
OF 75 KTS IS PLACED WITH HIGH CONFIDENCE AND IS HEDGED JUST BELOW 
BETWEEN MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T4.5 (77 
KTS, PGTW AND RJTD), A CIMSS ADVANCED DVORAK TECHNIQUE CURRENT 
INTENSITY ESTIMATE OF T4.4 (75 KTS). TY 16W IS TRACKING ALONG THE 
WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE 
EAST. TY 16W IS PASSING THROUGH AN OVERALL UNFAVORABLE ENVIRONMENT 
WITH MODERATE TO HIGH (25 KTS) VERTICAL WIND SHEAR (VWS) OFFSET BY 
WARM (27-28 CELSIUS) SEA SURFACE TEMPERATURES (SST) AND ROBUST 
POLEWARD OUTFLOW ALOFT, ENHANCED BY 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 TRACK GENERALLY NORTHEASTWARD 
OVER THE NEXT 24 HOURS. DURING THIS TIME, THE SYSTEM WILL GRADUALLY 
WEAKEN TO 60 KNOTS BY TAU 24, LARGELY DUE TO THE INCREASING VWS WHICH 
IS EXPECTED 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 36, CONTINUED HIGH VWS, COUPLED WITH COOL (23-25 
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 COLD CORE LOW. NUMERICAL MODEL SOLUTIONS 
HAVE CONTINUED TO STRUGGLE WITH THE LATER PORTION OF THE TRACK FOR 
16W. THE DETERMINISTIC GFS GUIDANCE AND JGSM BRINGS THE CYCLONE 
CENTER SOUTHEASTWARD, THEN DIRECTLY SOUTHWARD AFTER TAU 48, IN A 
TIGHT LOOP PAST IWO TO THROUGH A BREAK IN THE STR. HOWEVER, THE GFS 
ENSEMBLE MEAN LIES CLOSER TO THE REMAINING CONSENSUS MEMBERS. THE 
LARGE SPREAD IN MODEL SOLUTIONS LENDS POOR CONFIDENCE IN THE JTWC 
FORECAST, WHICH IS PLACED CLOSE TO THE JTWC MULTI-MODEL CONSENSUS.//
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