WDPN31 PGTW 200300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.6N 114.3E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 347 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A SLOWLY
CONSOLIDATING SYSTEM IN THE SOUTH CHINA SEA (SCS) WITH FORMATIVE,
FRAGMENTED BANDS LOOSELY FEEDING INTO A BROAD, MOSTLY OBSCURED, AND
ILL-DEFINED LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION,
EXTRAPOLATED FROM THE CURRENT STORM MOTION, IS PLACED WITH LOW 
CONFIDENCE BASED ON THE LLC IN THE MSI LOOP. THE INITIAL INTENSITY IS 
ASSESSED WITH HIGH CONFIDENCE BASED ON OVERALL ASSESSMENT OF AGENCY 
AND OBJECTIVE DVORAK ESTIMATES AND CONSISTENT WITH THE SUSTAINED 6-HR 
CONVECTIVE SIGNATURE. THE INITIAL POSITION AND ESTIMATE ARE ALSO 
CONSISTENT WITH SURFACE WIND OBSERVATIONS IN THE SCS. ENVIRONMENTAL 
ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH WARM SST AND MODERATE
EQUATORWARD OUTFLOW OFFSET BY MODERATE VERTICAL WIND SHEAR.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 200000Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TD 04W IS EXPECTED TO CONTINUE TRACKING
WEST-NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR TO THE
NORTHEAST, BECOMING MORE NORTHWESTWARD AFTER TAU 24 AS THE STR IS
WEAKENED BY A MID-LATITUDE TROUGH DIGGING IN FROM THE NORTHWEST. TD
04W WILL MAKE LANDFALL OVER HAINAN SHORTLY AROUND TAU 30, CROSS THE
GULF OF TONKIN, THEN WILL TRACK INTO SOUTHERN CHINA JUST BEFORE TAU 
72. THE MARGINALLY FAVORABLE ENVIRONMENT WILL PROMOTE A MODEST 
INTENSIFICATION TO A PEAK OF 45KTS BY TAU 24. AFTERWARD, LAND 
INTERACTION WITH HAINAN AND SOUTHERN CHINA WILL PRIMARILY ERODE THE 
SYSTEM TO DISSIPATION BY TAU 96. 
 

MODEL DISCUSSION: THE LIMITED NUMERICAL MODELS ARE IN GOOD AGREEMENT, 
GRADUALLY SPREADING OUT TO 217NM BY TAU 72 THEN BECOME ERRATIC AS THEY 
LOSE THE WEAKENED VORTEX. IN VIEW OF THIS AND GIVEN THE STRAIGHT-
FORWARD STEERING MECHANISM, THERE IS MEDIUM CONFIDENCE IN THE JTWC 
TRACK FORECAST UP TO TAU 72, THEN LOW CONFIDENCE AFTERWARD.

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
NNNN