WDPN31 PGTW 070900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (CHAN-HOM) WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 16W (CHAN-HOM), LOCATED APPROXIMATELY 378 NM EAST OF 
KADENA AB, OKINAWA, HAS TRACKED NORTHWESTWARD AT 11 KNOTS OVER THE 
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS 
A CONSOLIDATING SYSTEM WITH A RAGGED EYE, WHICH SUPPORTS THE INITIAL 
POSITION AND RECENT TRACK MOTION WITH GOOD CONFIDENCE. A 070435Z 
AMSR2 36GHZ MICROWAVE IMAGE INDICATES IMPROVED CONVECTIVE BANDING 
WRAPPING TIGHTLY INTO A MICROWAVE EYE FEATURE. THE INITIAL 
INTENSITY IS ASSESSED AT 65 KNOTS BASED ON PGTW/KNES DVORAK 
INTENSITY ESTIMATES OF T4.0 (65 KNOTS). ENVIRONMENTAL CONDITIONS 
REMAIN FAVORABLE WITH ENHANCED POLEWARD OUTFLOW, GOOD EQUATORWARD 
OUTFLOW, LOW (5-10 KT) VERTICAL WIND SHEAR (VWS), AND WARM (28-29 
CELSIUS) SEA SURFACE TEMPERATURES. 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. IMPORTANT NOTE: TY 16W HAS MAINTAINED 
EXTENSIVE GALE-FORCE WINDS AS LARGE AS 180NM RADIUS. TO FURTHER 
COMPLICATE THIS SCENARIO, THE SYSTEM IS TRACKING INTO A STRONG 
BAROCLINIC ZONE WITH ITS OWN TIGHT GRADIENT AS EVIDENCED BY 25 TO 35 
KNOT SURFACE WIND REPORTS ACROSS WESTERN JAPAN AND THE RYUKYU 
ISLANDS. THUS GALE-FORCE WINDS ARE POSSIBLE ALONG AND OUTSIDE THE 
PERIPHERY OF THE SYSTEM AS IT TRACKS CLOSER TO JAPAN.   
   B. TY 16W IS FORECAST TO TRACK NORTHWESTWARD TO NORTHWARD THROUGH 
TAU 48 AS IT RECURVES. NUMERICAL MODEL GUIDANCE IS IN BETTER 
AGREEMENT BUT STILL INDICATES SIGNIFICANT UNCERTAINTY IN THE TIMING 
AND POINT OF THE RECURVE WITH A 130NM SPREAD IN SOLUTIONS AT TAU 48.
AFTER TAU 48, THE SYSTEM WILL ACCELERATE NORTHEASTWARD AS IT BEGINS 
TO INTERACT WITH THE MIDLATITUDE WESTERLIES. THE 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 36-48. TY 16W IS FORECAST TO INTENSIFY TO A PEAK INTENSITY OF 80 
KNOTS BY TAU 24-36 UNDER FAVORABLE CONDITIONS. BASED ON THE COMPLEX 
STEERING PATTERN AND SPREAD IN SOLUTIONS, THERE IS FAIR 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 EAST-NORTHEASTWARD TRACK ALONG THE SOUTHERN COAST OF 
JAPAN. DUE TO HIGH (>35 KTS) VWS, TY 16W IS EXPECTED TO WEAKEN 
STEADILY FOR THE REMAINDER OF THE FORECAST PERIOD TO AN INTENSITY OF 
45 KTS BY TAU 120. TY 16W WILL BEGIN EXTRATROPICAL TRANSITION (ETT) 
BY TAU 72 AND WILL COMPLETE ETT BETWEEN TAU 96 AND TAU 120 AS IT 
GAINS FRONTAL CHARACTERISTICS. THE JTWC FORECAST TRACK IS POSITIONED 
ON THE SOUTHERN EDGE OF THE AIDS ENVELOPE CLOSE TO THE ECMWF 
SOLUTION AND THE OFFICIAL JMA FORECAST TRACK. DUE TO UNCERTAINTY IN 
THE TRACK AS THE SYSTEM UNDERGOES ETT, THERE IS FAIR CONFIDENCE 
(MODERATE UNCERTAINTY) IN THE JTWC FORECAST TRACK.//
NNNN