WDPN31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (CHOI-WAN) 
WARNING NR 025//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 04W (CHOI-WAN), LOCATED APPROXIMATELY 353 NM 
SOUTHWEST OF KADENA AB, HAS TRACKED NORTHEASTWARD AT 16 KNOTS OVER 
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS POCKETS OF WEAK CONVECTION AND MID LEVEL CLOUD LINES
OBSCURING THE LOW LEVEL CIRCULATION CENTER. THE INITIAL POSITION IS
PLACED WITH FAIR CONFIDENCE BASED ON THE ANALYSIS OF THE MID LEVEL 
CONVECTIVE FEATURES IN THE ANIMATED EIR AND COMPOSITE RADAR LOOPS. 
THE INITIAL INTENSITY OF 30 KTS IS PLACED WITH FAIR CONFIDENCE AND 
IS HEDGED BETWEEN MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATE OF 
T1.0 (25 KTS, PGTW) AND T2.0 (30 KTS, RJTD), AN ADVANCED DVORAK 
TECHNIQUE INTENSITY ESTIMATE OF T1.5 (25 KTS) AND A 041329Z CIMSS 
SATELLITE CONSENSUS INTENSITY ESTIMATE OF 43 KTS. IN ADDITION, A 
SHIP OBSERVATION IN THE VACINITY OF THE SYSTEM REPORTED 31 KTS WINDS 
ALONG THE SOUTHEAST PERIPHERY OF THE SYSTEM. TD CHOI-WAN IS TRACKING 
ALONG THE NORTHWESTERN PERIPHERY OF A SUB-TROPICAL RIDGE (STR) 
POSITIONED TO THE SOUTHEAST AND THROUGH A MARGINALLY FAVORABLE 
ENVIRONMENT WITH WARM (28-29 CELSIUS) SEA SURFACE TEMPERATURE VALUES 
AND LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS) OFFSET BY CONVERGENT 
AND ROBUST WESTERLY FLOW IN THE UPPER LEVELS. 
   A. THE FORECAST PHILOSOPHY HAS BEEN UPDATED TO REFLECT DISSIPATION
AT TAU 36, RATHER THAN EXTRATROPICAL TRANSITION.   
   B. TD CHOI-WAN WILL CONTINUE TO TRACK GENERALLY NORTHEASTWARD 
TOWARDS THE MEI-YU BOUNDARY POSITIONED NORTHWEST OF THE RYUKYU 
ISLANDS. AS THE SYSTEM APPROACHES THE BOUNDARY IT WILL BRIEFLY 
INTENSIFY TO 40 KTS BY TAU 12 DUE TO THE ADDED VORTICITY IMPARTED BY 
THE NORTHEASTERLY FLOW ALONG THE WESTERN PERIPHERY OF THE SHEAR 
LINE. THEREAFTER, VWS INCREASE DRAMATICALLY TO 40+ KTS. THIS 
INCREASED VWS, COUPLED WITH COOLING SST VALUES, WILL LEAD TO 
WEAKENING AFTER TAU 12 AND LEAD TO DISSIPATION OVER WATER BY TAU 36 
AT WHICH TIME THE SYSTEM WILL BECOME EMBEDDED IN THE MEI-YU 
BOUNDARY. NUMERICAL MODEL SOLUTIONS ARE IN GOOD AGREEMENT REGARDING 
STORM TRACK AND INTENSITY WITH THE MAJORITY OF DYNAMICAL MODELS 
AGREEING ON THE BRIEF INTENSIFICATION SCENARIO AT TAU 12. THIS HIGH 
DEGREE OF AGREEMENT IN MODEL SOLUTIONS LENDS OVERALL HIGH CONFIDENCE 
IN THE JTWC FORECAST TRACK, WHICH IS PLACED ALONG THE MULTI-MODEL 
CONSENSUS.//
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