WDPN31 PGTW 070300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING 
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 456 NM 
EAST OF KADENA AB, OKINAWA, HAS TRACKED WEST-NORTHWESTWARD AT 07 
KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL 
SATELLITE IMAGERY (MSI) REVEALS CONVECTIVE BANDING WRAPPING INTO THE 
LOW LEVEL CIRCULATION CENTER (LLCC), OBSCURED BY FLARING CONVECTION 
OVERHEAD. THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION, BASED ON 
AN EXTRAPOLATION OF A 062123Z SSMIS 37 GHZ MICROWAVE IMAGE DEPICTING 
A WELL-DEFINED MICROWAVE EYE FEATURE AND PLACED NEAR THE PGTW AND 
RJTD FIXES. THE INITIAL INTENSITY IS SET AT 60 KTS, HEDGED SLIGHTLY 
ABOVE MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T3.5 (55 
KTS) AND JUST UNDER A 062052Z SMAP WIND SPEED IMAGE DEPICTING 57 KTS 
(10-MINUTE AVERAGE)/63 KTS (1-MINUTE AVERAGE) WINDS. CURRENT 34-KT 
AND 50-KT WIND RADII HAVE BEEN UPDATED WITH RECENT ASCAT DATA. 
ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE AS TS 16W IS POSITIONED 
UNDER AN UPPER LEVEL POINT SOURCE CONTRIBUTING TO ENHANCED POLEWARD 
OUTFLOW AND GOOD EQUATORWARD OUTFLOW. ADDITIONALLY, LOW (5-10 KT) 
VERTICAL WIND SHEAR (VWS) AND WARM (29-30 CELSIUS) SEA SURFACE 
TEMPERATURES (SST) ARE CONDUCIVE FOR CONTINUED DEVELOPMENT. TS 16W 
IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE 
(STR) POSITIONED TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 16W IS FORECAST TO TRACK GENERALLY NORTHWESTWARD ALONG THE 
SOUTHWESTERN PERIPHERY OF THE STEERING STR THROUGH TAU 48, 
INTENSIFYING TO A PEAK OF 80 KTS BY TAU 36. TS 16W IS EXPECTED TO 
SLOW SIGNIFICANTLY AS IT APPROACHES THE RYUKYU ISLANDS AND BEGINS TO 
RECURVE AROUND THE STEERING STR. THE SPREAD IN THE NUMERICAL MODEL 
GUIDANCE NEAR THE RECURVE POINT REACHES 192 NM NEAR TAU 48 DUE TO 
THE PRESENCE OF A LARGE BREAK IN THE WESTERN AND EASTERN SUBTROPICAL 
RIDGES, ALONG WITH THE LACK OF A DYNAMIC MIDLATITUDE SHORTWAVE 
TROUGH, WHICH WOULD TYPICALLY ACCELERATE THE SYSTEM POLEWARD. AFTER 
TAU 48, THE SYSTEM WILL BEGIN TO CREST THE STR AXIS AND TURN TO A 
GENERALLY NORTH-NORTHEASTWARD TRACK THROUGH TAU 72. THE GLOBAL 
MODELS CURRENTLY DEPICT A ZONAL PATTERN WITH A SHORTWAVE RIDGE 
PROPAGATING OVER THE KOREAN PENINSULA NEAR TAU 60. AS THE SYSTEM 
TURNS TO THE NORTH-NORTHEASTWARD TRACK, IT WILL INTERACT WITH THIS 
ZONAL FLOW. BASED ON THE COMPLEX STEERING PATTERN AND MODERATE 
SPREAD IN SOLUTIONS, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE 
JTWC FORECAST TRACK.
   C. IN THE EXTENDED RANGE, TS 16W WILL TRACK NORTHEASTWARD ALONG 
THE SOUTHERN COAST OF JAPAN. DUE TO HIGH (>30 KTS) VWS ONSET 
BEGINNING AT TAU 72, TS 16W IS EXPECTED TO GRADUALLY WEAKEN FOR THE 
REMAINDER OF THE FORECAST PERIOD TO AN INTENSITY OF 50 KTS BY TAU 
120. DURING THIS TIME, TS 16W WILL BEGIN TO INTERACT WITH THE 
BAROCLINIC ZONE AND COMMENCE EXTRATROPICAL TRANSITION (ETT) BY TAU 
72. ETT COMPLETION IS EXPECTED BY TAU 120 AS THE SYSTEM GAINS 
FRONTAL CHARACTERISTICS AND BECOMES EMBEDDED IN THE WESTERLY FLOW. 
IN THE EXTENDED RANGE, THERE ARE LARGE VARIATIONS IN THE TRACK 
SPEEDS WITH GFS, GALWEM, AND GFS ENSEMBLE DISPLAYING SIGNIFICANTLY 
FASTER TRACK SPEEDS WHILE THE REMAINDER OF THE GUIDANCE INDICATES 
SLOWER TRACK SPEEDS. THE JTWC FORECAST TRACK HAS REMAINED FAIRLY 
CONSISTENT AND IS POSITIONED NEAR THE ECMWF AND ECMWF ENSEMBLE MEAN 
SOLUTIONS, IN LINE WITH THE MAJORITY OF THE MODEL SOLUTIONS. THE 
LATEST MODEL RUN REVEALED NAVGEM AS A SIGNIFICANT OUTLIER TO THE 
EAST THAT RECURVES SIGNIFICANTLY FASTER THAN THE MAJORITY OF THE 
MODEL SOLUTIONS. DUE TO THESE MODEL DIFFERENCES, THERE IS OVERALL 
LOW CONFIDENCE (HIGH UNCERTAINTY) IN THE JTWC FORECAST TRACK.//
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