WDPN31 PGTW 062100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING NR 
009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 509 NM 
EAST OF KADENA AB, OKINAWA, HAS TRACKED WEST-NORTHWESTWARD AT 08 KNOTS 
(KTS) OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE 
IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH IMPROVED DEEP CONVECTIVE 
BANDING WRAPPING INTO A DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC) 
OBSCURED BY FLARING DEEP CONVECTION. A 061711Z ATMS 88.2 GHZ MICROWAVE 
IMAGE REVEALS DEEP CONVECTION WRAPPING AROUND A BROAD LLCC AND 
SUPPORTS THE INITIAL POSITION WITH GOOD CONFIDENCE. THE INITIAL 
INTENSITY IS SET AT 55 KTS WITH GOOD CONFIDENCE BASED ON DVORAK 
CURRENT INTENSITY ESTIMATES OF T3.5 BY PGTW AND KNES AND HEDGED UNDER 
A 061740Z ADVANCED DVORAK TECHNIQUE ESTIMATE OF T3.8 (61 KTS) AND A 
061619Z SATCON ESTIMATE OF 66 KTS. ENVIRONMENTAL CONDITIONS REMAIN 
FAVORABLE AS TS 16W IS POSITIONED UNDER AN UPPER LEVEL POINT SOURCE 
WHICH IS 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 SLOWLY CONSOLIDATING AS 
IT TRACKS NORTHWESTWARD 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 72, 
INTENSIFYING TO A PEAK OF 80 KTS AT TAU 36. TS 16W IS FORECAST TO SLOW 
SIGNIFICANTLY AS IT APPROACHES THE RYUKYU ISLANDS WITH INCREASING 
UNCERTAINTY IN THE RECURVE POINT. AROUND TAU 60, THE SYSTEM SHOULD 
BEGIN TO ROUND THE STR. CURRENTLY, THERE IS A 151 NM SPREAD IN 
SOLUTIONS AT TAU 48 AND 223 NM AT TAU 72. THE VARIATION IN THE MODEL 
SOLUTIONS IS 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. THE GLOBAL MODELS CURRENTLY DEPICT A ZONAL PATTERN 
WITH A SHORTWAVE RIDGE PROPAGATING OVER THE KOREAN PENINSULA NEAR TAU 
60. ADDITIONALLY, THE GFS AND GFS ENSEMBLE SOLUTIONS DIVERGE AS A 
OUTLIERS TO THE EAST AFTER TAU 12 WITH THE UKMET ENSEMBLE SOLUTION 
TRACKING FURTHER WEST THAN THE MAJORITY OF THE NUMERICAL MODEL 
GUIDANCE. BASED ON THE COMPLEX STEERING PATTERN AND LARGE SPREAD IN 
SOLUTIONS, THERE IS LOW CONFIDENCE IN THIS PORTION OF THE JTWC 
FORECAST TRACK.
   C. AFTER TAU 72, THE SYSTEM WILL TURN TO A GENERALLY NORTHEASTWARD 
TRACK ALONG THE SOUTHERN COAST OF JAPAN. DUE TO HIGH (>30 KTS) VWS, TS 
16W IS EXPECTED TO GRADUALLY WEAKEN FOR THE REMAINDER OF THE FORECAST 
PERIOD TO AN INTENSITY OF 50 KTS BY TAU 120. TS 16W WILL BEGIN TO 
INTERACT WITH THE BAROCLINIC ZONE DURING THIS TIME AND COMMENCE 
EXTRATROPICAL TRANSITION. IN THE EXTENDED RANGE, THERE ARE MAJOR 
DIFFERENCES IN TRACK SPEEDS BETWEEN MODEL SOLUTIONS WITH GFS, NAVGEM 
AND THE GFS ENSEMBLE MEAN INDICATING SIGNIFICANTLY FASTER TRACK SPEEDS 
WHILE THE REMAINDER OF THE GUIDANCE INDICATES A SLOWER RECURVE. THE 
JTWC FORECAST TRACK IS POSITIONED CLOSE TO THE MULTI-MODEL CONSENSUS 
IN LINE WITH THE BULK OF THE NUMERICAL MODEL GUIDANCE. DUE TO THESE 
MODEL DIFFERENCES, THERE IS OVERALL LOW CONFIDENCE (HIGH UNCERTAINTY) 
IN THE JTWC FORECAST TRACK.//
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