WDPN31 PGTW 200900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (FOUR) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.9N 114.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 335 NM EAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 6 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION (TD) 04W (FOUR) WITH DISORGANIZED CONVECTION SCATTERED
AROUND THE OBSCURED LOW-LEVEL CIRCULATION CENTER (LLCC). THE SYSTEM
IS VERY BROAD IN NATURE WITH LARGE CONVECTIVE BANDS TRYING TO WRAP
INTO THE CENTER ALONG THE SOUTHERN PERIPHERY. ENVIRONMENTAL
ANALYSIS INDICATES THAT 04W IS IN A MARGINALLY FAVORABLE
ENVIRONMENT CHARACTERIZED BY MODERATE EQUATORWARD OUTFLOW ALOFT,
LOW TO MODERATE (15-20 KTS) VERTICAL WIND SHEAR, AND WARM (29-30 C)
SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS PLACED WITH LOW
CONFIDENCE BASED ON THE ANIMATED MSI. 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: 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: 34 KTS AT 200600Z
   CIMSS AIDT: 34 KTS AT 200600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 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 THROUGH TAU 72 ALONG THE SOUTHWESTERN PERIPHERY OF A
STR POSITIONED TO THE NORTHEAST. AFTER TAU 72, ONCE THE SYSTEM
MAKES LANDFALL ALONG THE SOUTHERN COAST OF CHINA, THE SYSTEM
QUICKLY DISSIPATES. 04W IS FORECAST TO PEAK AT 45 KTS AROUND TAU
36. SHEAR AND HINDERED OUTFLOW WILL BE THE MAIN SOURCES OF
HINDRANCE. AFTER TAU 36, LANDFALL OVER HAINAN WILL START A
WEAKENING TREND, WHICH CONTINUES FOR THE REMAINDER OF THE FORECAST
PERIOD.

MODEL DISCUSSION: WITH THE EXCEPTION OF UKMET, NUMERICAL MODEL
GUIDANCE IS IN GOOD AGREEMENT WITH A 80 NM CROSS-TRACK SPREAD
THROUGH TAU 72. AFTER TAU 72, THE VORTEX IS QUICKLY LOST AND MODELS
DIVERGE DRASTICALLY. THIS LENDS MEDIUM CONFIDENCE TO THE JTWC
FORECAST TRACK THROUGH TAU 72, AND LOW THEREAFTER. THE INTENSITY
GUIDANCE IS ALSO IN GOOD AGREEMENT WITH MODEST INTENSIFICATION,
WITH THE EXCEPTION OF HWRF, WHICH CALLS FOR A PEAK INTENSITY OF
AROUND 70 KTS AT TAU 60. THE JTWC FORECAST IS IN LINE WITH THE MAIN
GROUPING OF GUIDANCE AND IS ASSESSED WITH MEDIUM CONFIDENCE THROUGH
THE FORECAST PERIOD. 

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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