WDPN31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (CHAN-HOM) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 16W (CHAN-HOM), LOCATED APPROXIMATELY 434 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, 20 NM DIAMETER EYE. THE INITIAL POSITION IS PLACED WITH HIGH 
CONFIDENCE BASED ON THE EYE FEATURE IN THE EIR LOOP AND A MICROWAVE 
EYE FEATURE SEEN IN A 081724Z AMSR 89GHZ IMAGE. 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 AND RJTD), A CIMSS ADVANCED DVORAK TECHNIQUE CURRENT 
INTENSITY ESTIMATE OF T4.6 (80 KTS) AND A 081720Z CIMSS SATCON 
INTENSITY ESTIMATE OF 83 KTS. TY 16W IS TRACKING ALONG THE WESTERN 
PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST. TY 
16W IS NOW PASSING THROUGH AN ENVIRONMENT THAT IS NO LONGER 
FAVORABLE FOR FURTHER DEVELOPMENT WITH MODERATE TO HIGH (20-25 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 36, CONTINUED HIGH VWS, COUPLED WITH COOL (23-25 CELSIUS) SST 
WILL LEAD TO CONTINUED WEAKENING TO 55 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 CONTINUED TO STRUGGLE WITH THE LATER PORTION OF THE 
TRACK FOR 16W. THE DETERMINISTIC GFS GUIDANCE BRINGS THE CYCLONE 
CENTER SOUTHEASTWARD, THEN DIRECTLY SOUTHWARD AFTER TAU 48, IN A 
TIGHT LOOP PAST IWO TO. HOWEVER, THE GFS ENSEMBLE MEAN LIES CLOSER 
TO THE REMAINING CONSENSUS MEMBERS. IN THE REMAINING TRACK MEMBERS, 
THERE IS A 440 NM SPREAD BETWEEN AT TAU 72. 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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