WDPN33 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (KOMPASU) WARNING 
NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.5N 127.9E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 434 NM EAST-NORTHEAST OF MANILA,
PHILIPPINES
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A VERY LARGE 
MONSOON DEPRESSION WITH THE CENTRAL CONVECTION OFFSET 40+ NM POLEWARD 
FROM A BROAD, FULLY EXPOSED, BUT WELL-DEFINED LOW LEVEL CIRCULATION 
(LLC). THE LLC HAS VEERED AND BEGAN TO TRACK NORTHWESTWARD. ITS 
CENTRAL CONVECTION TRAILS LARGE SWATHS OF FORMATIVE RAIN BANDS 
EXTENDING ALL THE WAY DOWN TO THE SOUTHERN PHILIPPINES. THE INITIAL 
POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE LLC IN THE MSI 
LOOP. THE INITIAL INTENSITY OF 35KTS IS BASED WITH MEDIUM CONFIDENCE 
ON THE PGTW AND RJTD DVORAK ESTIMATES AND IS SUPPORTED BY RECENT
SCATTEROMETRY PASSES. ENVIRONMENTAL ANALYSES INDICATE MARGINALLY
FAVORABLE CONDITIONS FOR DEVELOPMENT CHARACTERIZED BY WARM SSTS IN
THE PHILIPPINE SEA AND STRONG POLEWARD OUTFLOW ALOFT OFFSET BY
STRONG (25-35KT) VWS. THE CYCLONE IS TRACKING ALONG THE SOUTHWESTERN 
PERIPHERY OF THE SUBTROPICAL RIDGE TO THE NORTHEAST.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA.

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS KOMPASU WILL CONTINUE ON ITS CURRENT TRACK
UP TO TAU 12. AFTERWARD, THE STR IS EXPECTED TO BUILD AND EXTEND
WESTWARD AND DRIVE THE SYSTEM DUE WESTWARD THROUGH THE LUZON
STRAIT, INTO THE SOUTH CHINA SEA (SCS), ACROSS HAINAN AND THE GULF
OF TONKIN BEFORE MAKING LANDFALL IN NORTHERN VIETNAM JUST BEFORE
TAU 96. THE MARGINALLY FAVORABLE ENVIRONMENT WILL FUEL GRADUAL
INTENSIFICATION TO A PEAK OF 70KTS IN THE SCS WHERE THE ENVIRONMENT
IS EXPECTED TO BE MORE FAVORABLE. AFTERWARD, INCREASING VWS WILL
SLOWLY WEAKEN THE SYSTEM DOWN TO 45KTS JUST BEFORE LANDFALL. AFTER
TAU 96, INTERACTION WITH THE RUGGED VIETNAMESE TERRAIN WILL RAPIDLY
ERODE THE SYSTEM DOWN TO 30KTS AFTER IT CROSSES INTO CAMBODIA.     

MODEL DISCUSSION: NUMERICAL MODELS ARE UNUSUALLY IN TIGHT AGREEMENT
FOR AN AN INITIAL WARNING. HOWEVER, GIVEN THE FORMATIVE NATURE OF
THE SYSTEM AND ITS LARGE LLC, THERE IS LOW CONFIDENCE IN THE
JTWC TRACK FORECAST UP TO TAU 120. CONSEQUENTLY, THERE IS MEDIUM
CONFIDENCE IN THE INTENSITY FORECAST UP TO TAU 72 THEN LOW
CONFIDENCE AFTERWARD. 

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