WDPN31 PGTW 072100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (CHAN-HOM) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 16W (CHAN-HOM), LOCATED APPROXIMATELY 281 NM
EAST OF KADENA AB, HAS TRACKED NORTHWESTWARD AT 09 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS 
FLARING CONVECTION PRIMARILY LOCATED POLEWARD OF A LARGE AND RAGGED 
30-NM EYE. THE SOUTHWESTERN EYE WALL HAS BECOME DISCONTINUOUS WITH 
SOME DRY AIR ENTRAINMENT OBSERVED. THE INITIAL WIND RADII CONTINUE 
TO CAPTURE BOTH THE TROPICAL CYCLONE WINDS AND A PORTION OF THE 
NORTHEASTERLY FRONTAL FLOW WRAPPING INTO THE SYSTEM. THE INITIAL 
INTENSITY REMAINS ASSESSED AT 70 KNOTS BASED ON AN AVERAGE OF 
PGTW/KNES DVORAK INTENSITY ESTIMATES OF T4.5 (77 KNOTS) AND AN RJTD 
ESTIMATE 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 240NM RADIUS. TO FURTHER 
COMPLICATE THIS SCENARIO, THE SYSTEM IS TRACKING INTO A STRONG 
BAROCLINIC ZONE WITH ITS OWN TIGHT GRADIENT AS EVIDENCED BY 30 TO 40 
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 HAS BEGUN TO TURN POLEWARD AND IS FORECAST TO TRACK 
NORTHWESTWARD TO NORTHWARD THROUGH TAU 36 AS IT RECURVES. NUMERICAL 
MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT, BUT THERE IS STILL 
UNCERTAINTY WITH HOW TIGHT THE TURN TOWARD THE NORTHEAST WILL BE, 
WHICH WILL GREATLY INFLUENCE THE POTENTIAL IMPACTS TO MAINLAND 
JAPAN. AFTER TAU 36, THE SYSTEM WILL ACCELERATE NORTHEASTWARD AS IT 
BEGINS TO INTERACT WITH THE MIDLATITUDE WESTERLIES. THE TRACK 
UNCERTAINTY IS EXACERBATED BY THE HIGH ZONAL FLOW, RESULTING IN THE 
EXPECTED SHARP TURN TOWARD THE NORTHEAST. TY 16W IS FORECAST TO 
INTENSIFY TO A PEAK INTENSITY OF 80 KNOTS BY TAU 24 GIVEN THE 
FAVORABLE ENVIRONMENTAL CONDITIONS, BUT THE CURRENT DISORGANIZATION 
OF THE INNER CORE OF TY 16W COULD PREVENT ANY FURTHER 
INTENSIFICATION FROM OCCURRING. BASED ON THE ZONAL 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 ACCELERATE EAST-NORTHEASTWARD 
ALONG AND NEAR THE SOUTHERN COAST OF JAPAN. DUE TO HIGH VERTICAL 
WIND SHEAR (>35 KTS), TY 16W IS EXPECTED TO WEAKEN STEADILY FOR THE 
REMAINDER OF THE FORECAST PERIOD TO AN INTENSITY OF 50 KTS BY TAU 
96. TY 16W WILL COMPLETE EXTRATROPICAL TRANSITION (ETT) BY TAU 96 AS 
IT GETS ABSORBED INTO THE BAROCLINIC ZONE. THE JTWC FORECAST 
TRACK CLOSELY FOLLOWS THE MULTI-MODEL CONSENSUS. DUE TO UNCERTAINTY 
IN THE TRACK AS THE SYSTEM UNDERGOES ETT, THERE IS FAIR CONFIDENCE 
IN THE JTWC FORECAST TRACK. ALL INTERESTS IN THE KANTO PLAIN REGION 
OF JAPAN SHOULD PAY CLOSE ATTENTION TO THE TIMING OF THE 
NORTHEASTWARD TURN AND EVOLUTION OF THE WIND FIELD, GIVEN THE 
POSSIBILITY THAT ANY MINOR FORECAST TRACK SHIFT TOWARD THE WEST 
WOULD BRING THE CORE OF TY 16W ASHORE.//
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