WDPN31 PGTW 060900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING 
NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 586 NM 
EAST OF KADENA AB, OKINAWA, HAS TRACKED NORTHWESTWARD AT 04 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY 
DEPICTS FRAGMENTED CONVECTIVE BANDING WRAPPING INTO A BROAD, 
PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). A 060618Z 
SSMI 37GHZ MICROWAVE IMAGE REVEALS RAGGED SHALLOW BANDING WRAPPING 
INTO THE BROAD LLCC, WHICH SUPPORTS THE INITIAL POSITION WITH FAIR 
CONFIDENCE. THE INITIAL INTENSITY REMAINS ASSESSED AT 45 KNOTS BASED 
ON DVORAK CURRENT INTENSITY ESTIMATES OF 3.0 (45 KNOTS) AND A RECENT 
ASCAT IMAGE SHOWING EXTENSIVE GALE-FORCE WINDS, PARTICULARLY OVER 
THE EASTERN SEMICIRCLE, WITH A PATCH OF 45-50 KNOT MAXIMUM WINDS 
OVER THE EASTERN QUADRANT. ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE 
WITH ENHANCED POLEWARD OUTFLOW, GOOD EQUATORWARD OUTFLOW, LOW (5-10 
KT) VERTICAL WIND SHEAR (VWS), AND WARM (29-30 CELSIUS) SEA SURFACE 
TEMPERATURES. HOWEVER, TS 16W IS SLOWLY CONSOLIDATING DUE TO THE 
BROAD NATURE OF THE LLCC. THE SYSTEM 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 72, 
INTENSIFYING AT A SLOWER-THAN-CLIMATOLOGICAL RATE TO A PEAK OF 80 
KTS AT TAU 72. TS 16W IS FORECAST TO SLOW SIGNIFICANTLY AS IT 
APPROACHES THE RYUKYU ISLANDS WITH INCREASING UNCERTAINTY IN THE 
RECURVE POINT. THERE IS CURRENTLY A 160NM SPREAD IN SOLUTIONS AT TAU 
72. THIS UNCERTAINTY IN THE NUMERICAL MODEL SOLUTIONS IS DUE TO THE 
PRESENCE OF A LARGE BREAK IN THE WESTERN AND EASTERN SUBTROPICAL 
RIDGES AND THE LACK OF A DYNAMIC MIDLATITUDE SHORTWAVE TROUGH, WHICH 
WOULD TYPICALLY ACCELERATE THE SYSTEM POLEWARD. IN FACT, THE GLOBAL 
MODELS DEPICT A ZONAL PATTERN WITH A SHORTWAVE RIDGE PROPAGATING 
OVER THE KOREAN PENINSULA NEAR TAU 60-72. THE 06/0000Z ECMWF 
ENSEMBLE ALSO INDICATES A LARGE DEGREE OF UNCERTAINTY IN THE RECURVE 
POINT NEAR THE RYUKYU ISLANDS. 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 ROUND THE STR AXIS AND 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, THE ALONG-TRACK SPREAD HAS INCREASED AT TAU 120 DUE 
TO THE UNCERTAINTY IN THE TIMING OF THE RECURVE. THUS, THERE IS ONLY 
FAIR CONFIDENCE IN THE REMAINDER OF THE JTWC FORECAST TRACK.//
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