WDPN31 PGTW 061500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING 
NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 552 NM 
EAST-SOUTHEAST OF KADENA AB, OKINAWA, HAS TRACKED WESTWARD AT 05 
KNOTS 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).
A 061136Z AMSU 89GHZ MICROWAVE IMAGE, HOWEVER, INDICATES THAT THE 
CONVECTIVE BANDING REMAINS FRAGMENTED. A 061137Z ASCAT-B BULLSEYE 
IMAGE SUPPORTS THE INITIAL POSITION WITH GOOD CONFIDENCE AND SHOWS 
EXTENSIVE GALE-FORCE WINDS SURROUNDING A WELL-DEFINED CENTER WITH 50-
55 KNOT WINDS OVER THE EASTERN QUADRANT. THIS IMAGE WAS USED TO 
ADJUST THE INITIAL 34-KNOT AND 50-KNOT WIND RADII. THE INITIAL 
INTENSITY IS ASSESSED AT 55 KNOTS BASED ON PGTW/KNES DVORAK 
INTENSITY ESTIMATES OF T3.5 (55 KNOTS) AS WELL AS THE ASCAT DATA. 
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 48. TS 16W IS FORECAST TO SLOW SIGNIFICANTLY AS IT 
APPROACHES THE RYUKYU ISLANDS WITH INCREASING UNCERTAINTY IN THE 
RECURVE POINT. THERE IS CURRENTLY A 200NM 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, THERE ARE MAJOR DIFFERENCES IN TRACKS SPEEDS 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. OVERALL, THERE IS LOW CONFIDENCE (HIGH UNCERTAINTY) IN THE 
JTWC FORECAST TRACK.//
NNNN