WDPN33 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (KOMPASU) WARNING 
NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.8N 117.4E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 276 NM SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 21 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A VERY LARGE
(GREATER THAN 10 DEGREE DIAMETER) SYSTEM WITH EXTENSIVE DEEP
CONVECTIVE BANDING WRAPPING INTO A LARGE RAGGED CENTER
(APPROXIMATELY 110NM DIAMETER). DUE TO THE VERY LARGE NATURE OF
THIS SYSTEM, GALE-FORCE WINDS EXTEND OUT ALONG THE PERIPHERY NEAR
TAIWAN AND SOUTHWEST OF LUZON. A 120600Z AMSR2 89GHZ MICROWAVE
IMAGE INDICATES FRAGMENTED CONVECTIVE BANDS WRAPPING AROUND THE
WESTERN SEMICIRCLE OF THE LARGE LOW-LEVEL CIRCULATION CENTER, WHICH
SUPPORTS THE INITIAL POSITION WITH MEDIUM CONFIDENCE. THE INITIAL
INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK ESTIMATES. UPPER-LEVEL ANALYSIS INDICATES A
MARGINALLY FAVORABLE ENVIRONMENT WITH LOW TO MODERATE VERTICAL WIND
SHEAR (VWS) OFFSET BY STRONG EQUATORWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
ENTRENCHED OVER CENTRAL CHINA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 59 KTS AT 120540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 24W IS FORECAST TO TRACK
WESTWARD THROUGH THE FORECAST PERIOD UNDER THE STEERING INFLUENCE
OF THE STR. TS 24W WILL STRENGTHEN TO A PEAK OF 60 KNOTS BY TAU 12
THEN GRADUALLY WEAKEN AS VWS INCREASES. AS THE SYSTEM TRACKS OVER
HAINAN AFTER 24, IT WILL WEAKEN SIGNIFICANTLY WITH MORE RAPID
WEAKENING EXPECTED AS THE SYSTEM MAKES LANDFALL OVER VIETNAM AFTER
TAU 48. DISSIPATION WILL OCCUR BY TAU 96 AS THE SYSTEM TRACKS
INLAND.     

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT THROUGH TAU 36 WITH A 50NM SPREAD IN SOLUTIONS AT TAU 36.
THE MODELS DIVERGE AFTER TAU 36 BUT REMAIN IN GOOD AGREEMENT
LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.  

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