WDPS31 PGTW 290300						
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (EIGHTEEN)
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.4S 173.7E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 413 NM SOUTHWEST OF SUVA, FIJI
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL CYCLONE (TC) 18P BEGINNING TO DECOUPLE FROM THE 
DEEP CONVECTION, WITH THE LOWER-LEVEL CIRCULATION CENTER (LLCC) 
BEGINNING TO PEEK OUT FROM UNDER THE CENTRAL DENSE OVERCAST (CDO).
THE ENVIRONMENT IS BEGINNING TO BECOME LESS FAVORABLE, WITH 18P 
ENTERING INTO A REGION OF HIGHER SHEAR AS IT TRACKS FARTHER 
SOUTHWARD. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE 
BASED ON THE PARTIALLY EXPOSED NATURE OF THE LLCC. THE INTIIAL
INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON 
THE AGENCY DVORAK FIXES AND CIMSS AUTOMATED INTENSITY AIDS
LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE.				

CURRENT STEERING MECHANISM: A SUBTROPICAL RIDGE (STR) CENTERED T0 
THE SOUTHWEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS ADT: 55 KTS AT 290120Z	
   CIMSS AIDT: 44 KTS AT 290120Z
   CIMSS DPRINT: 57 KTS AT 290120Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 30+ KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD					

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: NO SIGNIFICANT FORECAST CHANGES. 				

FORECAST DISCUSSION: TC 18P WILL CONTINUE TRACKING GENERALLY 
SOUTHWARD FOR THE NEXT 12 HOURS BEFORE CURVING TO THE 
SOUTHWEST AS IT ROUNDS THE SOUTHEASTERN PERIPHERY OF THE
STEERING RIDGE. 18P WILL THEN MAINTAIN A SOUTHWESTWARD TRACK 
THROUGH THE END OF THE FORECAST PERIOD AT TAU 24. REGARDING 
INTENSITY, 18P WILL QUICKLY WEAKEN AS IT ENTERS INTO A HOSTILE 
ENVIRONMENT CHARACTERIZED BY HIGHER SHEAR, COOLER SEA SURFACE 
TEMPERATURES, AND DRIER AIR. THE DRY AIR AND SHEAR WILL CAUSE THE 
VORTEX TO SHALLOW AND COME UNDER THE INFLUENCE OF EASTERLY
FLOW ALONG THE NORTH SIDE OF A RIDGE POSITIONED IN THE TASMAN SEA.
IT WILL ALSO BEGIN SUBTROPICAL TRANSITION (STT) UNDER THESE 
CONDITIONS, HOWEVER, FULL DISSIPATION IS ANTICIPATED BEFORE 18P CAN 
COMPLETE STT, NO LATER THAN TAU 24.

MODEL DISCUSSION: DETERMINISTIC TRACK MODEL GUIDANCE IS IN GOOD
AGREEMENT IN A SOUTH TO SOUTHWESTWARD TRACK THROUGH TAU 24,
SUPPORTING THE JTWC TRACK FORECAST WITH HIGH CONFIDENCE. RELIABLE
INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT 18P HAS BEGUN TERMINALLY
WEAKENING, SUPPORTING THE JTWC INTENSITY FORECAST WITH HIGH 
CONFIDENCE.

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