WDPN31 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.1N 115.7E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 309 NM WEST OF MANILA, PHILIPPINES
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A
MEDIUM-SIZED SYSTEM IN THE SOUTH CHINA SEA (SCS) THAT IS SLOWLY
CONSOLIDATING WITH FORMATIVE, FRAGMENTED BANDS LOOSELY WRAPPING
INTO A BROAD, PARTIALLY EXPOSED LOW LEVEL CIRCULATION (LLC). THE
INITIAL POSITION, CONSISTENT WITH CURRENT STORM MOTION, IS PLACED
WITH MEDIUM CONFIDENCE BASED ON THE LLC FEATURE IN THE EIR LOOP.
THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON A
191415Z PARTIAL ASCAT PASS SHOWING A PATCH OF 30-KT WIND BARBS 50NM 
AHEAD OF THE LLC AND SUPPORTED BY THE 191500Z DPRINT OBJECTIVE DVORAK 
ESTIMATE. THE INITIAL POSITION AND ESTIMATE ARE CONSISTENT WITH 
SURFACE WIND OBSERVATIONS IN THE SCS. ENVIRONMENTAL ANALYSIS INDICATES 
A MARGINALLY 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: T1.5 - 25 KTS
   CIMSS DPRINT: 191500Z - 28KTS 

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING
MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY.

FORECAST DISCUSSION: TD O4W 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
O4W WILL MAKE LANDFALL OVER HAINAN SHORTLY AFTER TAU 48 THEN TRACK
INTO SOUTHERN CHINA. THE MARGINALLY FAVORABLE ENVIRONMENT WILL
PROMOTE A MODEST INTENSIFICATION TO A PEAK OF 45KTS BY TAU 48.
AFTERWARD, LAND INTERACTION WILL PRIMARILY ERODE THE SYSTEM TO
DISSIPATION BY TAU 96.  

MODEL DISCUSSION: THE LIMITED NUMERICAL MODELS ARE IN BROAD
AGREEMENT UP TO 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//
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