WDPN31 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (PRAPIROON) WARNING 
NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.1N 108.0E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 118 NM EAST OF HANOI, VIETNAM
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
INCREASINGLY DISORGANIZED DEEP CONVECTION TRACKING SOUTHWEST, WITH
THE LOW-LEVEL CIRCULATION CENTER (LLCC) BECOMING PARTIALLY EXPOSED
IN THE LAST FEW FRAMES OF THE IMAGERY AND TRACKING
NORTH-NORTHWESTWARD. ENVIRONMENTAL ANALYSIS INDICATES THAT TROPICAL
STORM (TS) 04W HAS BECOME DECAPITATED OVER THE LAST SIX HOURS,
FURTHER SUPPORTED BY RADAR IMAGERY DEPICTING THE LLCC COMPLETELY
DISLOCATED FROM THE UPPER-LEVEL CIRCULATION, LIKELY ATTRIBUTED TO
UNFAVORABLE ELEVATED 20-25KT VERTICAL WIND SHEAR (VWS) FROM THE
NORTHEAST. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE
BASED ON THE AFOREMENTIONED ANIMATED EIR AND RADAR IMAGERY. THE
INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE
BASED ON THE OBJECTIVE AND AGENCY FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: ON THE WESTERN PERIPHERY OF A
SUBTROPICAL RIDGE TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 72 KTS AT 1630Z
   CIMSS ADT: 79 KTS AT 1800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 04W (PRAPIROON) IS FORECAST TO CONTINUE
TRACKING NORTH-NORTHWESTWARD ON THE WESTERN PERIPHERY OF A
DEEP-LAYER SUBTROPICAL RIDGE AS IT FURTHER BECOMES DECAPITATED BY
THE NORTHEASTERLY ELEVATED VWS THAT IS EXPECTED TO INCREASE TO
25-30KTS. ONCE MAKING LANDFALL, THE SYSTEM IS EXPECTED TO CURVE TO
THE SOUTHWEST THROUGH THE END OF THE FORECAST PERIOD DUE TO LAND
INTERACTION ON THE LOW-LEVELS. SEA SURFACE TEMPERATURES (SST) WILL
REMAIN FAVORABLE BETWEEN 29-30C NEAR LAND. OUTFLOW WILL NOT BE
FAVORABLE AS THE UPPER-LEVELS BECOME FURTHER DISLOCATED FROM THE
LLCC. INFLUENCED BY THE ELEVATED VWS, TC 04W IS EXPECTED TO WEAKEN
AS IT APPROACHES LANDFALL, AND ONCE MAKING LANDFALL, THE LAND
INTERACTION WILL CONTINUE TO FORCE THE LLCC TO BECOME DISORGANIZED
AND WEAK. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL CONTINUE TO TRACK NORTH-NORTHWESTWARD UNDER
THE INFLUENCE OF THE SUBTROPICAL RIDGE TO THE EAST. ONCE MAKING
LANDFALL, THERE ARE DIFFERENT VARIATIONS WHETHER THE SYSTEM WILL
TRACK NORTHEAST OR SOUTHWEST BASED ON HOW DIFFERENTLY THE SYSTEM
INTERACTS WITH LAND. THE JTWC TRACK CONSENSUS MOST CLOSELY ALIGNS
WITH THE JTWC FORECAST, TAKING THE TRACK TO THE SOUTHWEST AT TAU
48. THE FEW MEMBERS WHO DO TRACK NORTHEAST ARE JGSM AND COAMPS-TC. 

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