WDPN31 PGTW 201500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING 
NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.3N 113.3E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 289 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 9 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
TROPICAL DEPRESSION (TD) 04W (FOUR) AS APPEARING TO CONSOLIDATE OVER 
THE PAST 6 HOURS. THE SYSTEM REMAINS BROAD, BUT CONVECTION IS 
BECOMING A BIT MORE LOCALIZED TO THE CENTER OF THE SYSTEM. 
ENVIRONMENTAL ANALYSIS INDICATES THAT 04W IS IN A FAVORABLE 
ENVIRONMENT CHARACTERIZED BY MODERATE EQUATORWARD OUTFLOW ALOFT, LOW 
(10-15 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C) SEA SURFACE
TEMPERATURES. THE INITIAL POSITION IS PLACED WITH LOW CONFIDENCE
BASED ON THE ANIMATED EIR AND OBSCURED NATURE OF THE LOW-LEVEL
CIRCULATION CENTER (LLCC). THE INITIAL INTENSITY OF 30 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SUBJECTIVE AND
OBJECTIVE DVORAK ESTIMATES LISTED BELOW.

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

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A 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 SATCON: 35 KTS AT 201300Z
   CIMSS ADT: 35 KTS AT 201200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   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 FORECAST TO CONTINUE TRACKING
NORTHWESTWARD THROUGHOUT THE FORECAST PERIOD ALONG THE SOUTHWESTERN
PERIPHERY OF A STR POSITIONED TO THE NORTHEAST. 04W IS FORECAST TO 
PEAK AT 45 KTS AROUND TAU 36. THE SHORT WINDOW OF INTENSIFICATION 
BEFORE LANDFALL WILL BE THE PREVENTATIVE FACTOR IN ANY FURTHER 
INTENSIFICATION. AFTER TAU 36, LANDFALL OVER HAINAN WILL START A 
WEAKENING TREND THAT PERSISTS FOR THE REMAINDER OF THE FORECAST 
PERIOD. ONCE THE SYSTEM MAKES LANDFALL ALONG THE SOUTHERN COAST OF 
CHINA IT WILL QUICKLY DISSIPATE. 

MODEL DISCUSSION: WITH THE EXCEPTION OF UKMET ENSEMBLE, NUMERICAL
MODEL GUIDANCE IS IN GOOD AGREEMENT WITH A TIGHT CROSS-TRACK SPREAD
THROUGHOUT THE FORECAST PERIOD. THIS LENDS HIGH CONFIDENCE TO THE
JTWC FORECAST TRACK. THE INTENSITY GUIDANCE IS ALSO IN GOOD
AGREEMENT WITH MODEST INTENSIFICATION AND A PEAK RANGING FROM 40-50
KTS. HWRF AND HAFS-A BOTH MAINTAIN AN INTENSITY OF AROUND 30 KTS AT
TAU 72, WHICH DIFFERS FROM THE REST OF THE GUIDANCE THAT CALLS FOR
A QUICKER DISSIPATION. AS A RESULT, THE JTWC INTENSITY FORECAST IS
ASSESSED WITH MEDIUM CONFIDENCE.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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