WDPN31 PGTW 080300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 02W (NEPARTAK)
WARNING NR 21//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 02W (NEPARTAK), LOCATED APPROXIMATELY 155 NM SOUTH-
SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED WESTWARD AT 09 KNOTS
OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED ON SATELLITE
EYE FIXES FROM PGTW AND RJTD AS WELL AS RADAR IMAGERY FROM TAIWAN.
THE SATELLITE FIXES CONTINUE TO BE DOWNSTREAM OF THE RADAR-INDICATED
LOW-LEVEL CIRCULATION CENTER (LLCC), WITH THE LLCC BEING DISRUPTED
BY TOPOGRAPHIC INTERACTION WITH THE CENTRAL MOUNTAIN RANGE AND BEING
DEFLECTED WESTWARD. THIS SUGGESTS THAT THE MID-LEVEL CIRCULATION HAS
BECOME DECOUPLED AND IS MOVING AHEAD OF THE LLCC. GIVEN THESE
DYNAMICAL CHANGES IN THE SYSTEM, CONFIDENCE IN THE CURRENT POSITION
HAS DECREASED SINCE THE LAST WARNING. INTENSITY IS ESTIMATED AT 90
KNOTS, BASED ON SUBJECTIVE DVORAK SATELLITE INTENSITY ESTIMATES FROM
RJTD AND SURFACE OBSERVATIONS FROM SOUTHERN TAIWAN. STATION RCFN ON
THE SOUTHEAST COAST OF TAIWAN OBSERVED SUSTAINED WINDS AT 072100Z OF
70 KNOTS GUSTING TO 99 KNOTS WITH A SURFACE PRESSURE OF 964 MB. TY
02W IS EXPECTED TO CONTINUE TO RAPIDLY WEAKEN AS ITS CIRCULATION
INTERACTS WITH THE COMPLEX TOPOGRAPHY OF TAIWAN, PARTICULARLY WITH
THE LLCC BEING SIGNIFICANTLY DISRUPTED.
3. FORECAST REASONING.
   A. THE LLCC OF TY 02W HAS JOGGED TOWARD THE WEST IN RESPONSE TO
INTERACTION WITH SOUTHERN TAIWAN, BUT IF THE CIRCULATION CAN BECOME
VERTICALLY COHERENT AS THE SYSTEM EMERGES INTO THE TAIWAN STRAIT, TY
02W SHOULD RESUME A WEST-NORTHWESTWARD TRAJECTORY WITH A TURN TOWARD
THE NORTHWEST INTO A WEAKNESS IN THE SUBTROPICAL RIDGE INDUCED BY A
MID-LATITUDE TROUGH AXIS CURRENTLY PASSING THROUGH THE KOREAN
PENINSULA.
   B. ONCE TY 02W EMERGES OVER THE TAIWAN STRAIT AND REGAINS A
VERTICALLY COHERENT CIRCULATION, THE WEAKENING TREND IS EXPECTED TO
SLOW BUT CONTINUE, FOLLOWED BY A SECOND LANDFALL IN MAINLAND CHINA
SHORTLY AFTER TAU 24. BY TAU 36, STY 02W WILL WEAKEN OVER EASTERN
CHINA AS IT GRADUALLY TURNS TOWARD THE NORTH, WITH DISSIPATION
EXPECTED BY TAU 48. NUMERICAL MODEL GUIDANCE IS IN
GOOD AGREEMENT THROUGH THE FORECAST PERIOD, RESULTING IN FAIRLY HIGH
CONFIDENCE, BUT THE JTWC TRACK FORECAST LIES ALONG THE WESTERN
ENVELOPE OF THE NUMERICAL GUIDANCE IN THE NEAR TERM (TAU 12-24) TO
ACCOUNT FOR THE RECENT WESTWARD MOVEMENT OF THE LLCC AS IT PASSES
AROUND THE MOUNTAINS OF SOUTH-CENTRAL TAIWAN./=