Tropical Storm CHAN-HOM Advisory Sat Oct 10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (CHAN-HOM)
WARNING NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 16W (CHAN-HOM), LOCATED APPROXIMATELY 413 NM
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT
07 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS SPIRAL BANDS OF DEEP CONVECTION WRAPPING INTO
AN OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL
POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON THE BANDING IN THE
MSI LOOP AS WELL AS THE LOW LEVEL FEATURES PRESENT IN A 090438Z ATMS
88.2GHZ IMAGE. THE INITIAL INTENSITY OF 70 KTS IS PLACED WITH HIGH
CONFIDENCE AND IS HEDGED BETWEEN MULTI-AGENCY DVORAK CURRENT
INTENSITY ESTIMATES OF T4.0 (65 KTS, PGTW), T4.5 (77 KTS, RJTD) AND
A 090437Z CIMSS SATCON INTENSITY ESTIMATE OF 65 KTS. TY CHAN-HOM
IS TRACKING ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR)
POSITIONED TO THE EAST AND 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 EAST-NORTHEASTWARD OVER THE
NEXT 24 HOURS. DURING THIS TIME, THE SYSTEM WILL GRADUALLY
WEAKEN TO 55 KNOTS BY TAU 24, LARGELY DUE TO INCREASING VWS WHICH
IS EXPECTED EXCEED 30 KTS BY TAU 24. AFTER THIS TIME, THE TRACK WILL
BECOME GENERALLY EAST-NORTHEASTWARD TO EASTWARD AS THE SYSTEM TRACKS
ALONG THE NORTHERN PERIPHERY OF THE STEERING STR AND APPROACHES THE
BAROCLINIC ZONE. BY TAU 36, CONTINUED HIGH VWS WILL LEAD TO FURTHER
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 TY 16W, HOWEVER THEY ARE
BEGINNING TO CONVERGE ON A SOLUTION WHICH BRINGS THE CYCLONE CENTER
ON A SOUTHEASTWARD TRACK AFTER TAU 36 DUE TO A REPOSITIONING OF THE
STEERING RIDGE AFTER THIS TIME. SPECIFICALLY, THERE IS A 160 NM
SPREAD IN ACROSS TRACK SOLUTIONS AT TAU 36 THAT INCREASES TO 585 NM
BY TAU 72. DUE TO THE THE LARGE SPREAD IN MODEL SOLUTIONS THERE IS
OVERALL POOR CONFIDENCE IN THE JTWC FORECAST, WHICH IS PLACED CLOSE
TO THE JTWC MULTI-MODEL CONSENSUS.//
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