Tropical Storm CHAN-HOM Advisory vie, 09-10

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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