WDPN31 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 01W (DUJUAN) WARNING
NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 01W (DUJUAN), LOCATED APPROXIMATELY 518 NM 
SOUTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST-NORTHWESTWARD
AT 17 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) SHOWS DEEP, EXPANSIVE, FLARING CONVECTION OVER 
SOUTHEASTERN PHILIPPINES AND AHEAD OF THE LOW LEVEL CIRCULATION 
(LLC). INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON LOW 
CLOUD TRACING INTO THE LLC IN THE MSI LOOP AND LINED UP WITH A RAGGED 
LLC FEATURE IN THE 210425Z AMSR2 MICROWAVE IMAGE. THE INITIAL INTENSITY 
OF 35KTS IS BASED ON AN OVERALL ASSESSMENT OF AGENCY DVORAK ESTIMATES 
OF T1.0/25KTS (KNES), T2.0/30KTS (RJTD), T2.5/35KTS (PGTW), AND 
OBJECTIVE ADT OF T3.2/47KTS, AND REFLECTS THE 6-HR CONVECTIVE 
IMPROVEMENT. ANALYSIS INDICATES WARM (29C) ALONG-TRACK SST IN THE 
PHILIPPINE SEA AND ROBUST WEST AND POLEWARD OUTFLOW ALOFT. A SLIGHT 
DECREASE IN VWS DUE TO THE STORM MOTION MOVING MORE IN-PHASE WITH THE 
MID AND UPPER LEVEL WIND FLOW HAS ENHANCED THE CONVECTION AHEAD OF THE 
LLC. ADDITIONALLY, THE WARM MOIST AIR AHEAD OF THE TS IS CONTINUALLY 
OVERRUNNING THE COLDER NORTHEASTERLY WIND IN THE PHILIPPINE SEA 
INCREASING THE INSTABILITY. THE CYCLONE IS TRACKNG UNDER THE STEERING 
INFLUENCE OF THE SUBTROPICAL RIDGE (STR) TO THE NORTHEAST.  
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE IN THE FORECAST PHILOSOPHY FROM 
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS DUJUAN WILL CONTINUE TRACKING NORTHWESTWARD UNDER THE STR, 
MAKING INITIAL LANDFALL OVER LEYTE, PHILIPPINES, AFTER TAU 12 AND THEN 
CROSS THE VISAYAN ISLANDS, CLIPPING THE SOUTHERN TIP OF MINDORO, BEFORE 
EXITING INTO THE SOUTH CHINA SEA. THE SYSTEM WILL MAINTAIN ITS CURRENT 
INTENSITY UP TO TAU 12; AFTERWARD, INCREASED RELATIVE VWS (25KTS+) 
COMBINED WITH THE RUGGED TERRAIN OF THE ISLANDS WILL ERODE THE TS TO 
DISSIPATION BY TAU 48, POSSIBLY SOONER. NUMERICAL MODELS DIVERGE AND 
BIFURCATE TO 320NM+ BY TAU 48 WITH NAVGEM, UKMET, AND JGSM OFFERING A 
MORE POLEWARD SOLUTION AND THE REMAINDER OF THE MODEL ENVELOPE, 
INCLUDING ECMWF AND GFS, OFFERING A MORE EQUATORWARD TRACK. THIS 
INDICATES UNCERTAINTY IN THE MODELS TRACKING A WEAK VORTEX, LENDING 
OVERALL LOW CONFIDENCE IN THE JTWC TRACK FORECAST BEYOND TAU 24.//
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