WDPS31 PGTW 282100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (EIGHTEEN) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.4S 173.8E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 327 NM SOUTHWEST OF SUVA, FIJI
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 23 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 18P WITH A RADIALLY EXPANDING CENTRAL DENSE OVERCAST (CDO)
WITH STRONG POLEWARD OUTFLOW FEEDING INTO THE UPPER LEVEL TROUGH TO
IT'S SOUTHWEST. 18P HAS INTENSIFIED, DESPITE THE NORTHWESTERLY
VERTICAL WIND SHEAR (VWS) REMAINING HIGH (30+ KTS) AND THE DRY
ENVIRONMENT LOCATED DIRECTLY TO THE NORTHWEST, SUPPORTED BY WARM
(27-28 C) SEA SURFACE TEMPERATURES (SST) AND ROBUST DIVERGENCE
ALOFT. ADDITIONALLY, 18P HAS A DISTINCT OUTFLOW BOUNDARY --
PARTICULARLY ON THE UPSHEAR SIDE OF THE CIRCULATION -- SUPPLYING
SUPPORTING EVIDENCE THAT 18P IS RESISTING THE VWS AND DRY AIR TO
SOME DEGREE; HOWEVER, A 281818Z SSMIS 91GHZ MICROWAVE IMAGE REVEALS
THE VORTEX IS TILTED TO THE SOUTH WITH HEIGHT. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE BASED ON THE 281818Z MICROWAVE
IMAGE. THE INITIAL INTENSITY OF 55 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND CIMMS AUTOMATED
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) CENTERED TO THE
SOUTHWEST 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   PHFO: T3.5 - 55 KTS
   CIMSS ADT: 53 KTS AT 281900Z
   CIMSS AIDT: 44 KTS AT 281900Z
   CIMSS D-MINT: 49 KTS AT 281817Z
   CIMSS D-PRINT: 65 KTS AT 281900Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 18P IS FORECAST TO CONTINUE GENERALLY
SOUTHWARD FOR THE NEXT 12 HOURS BEFORE GENTLY CURVING TO THE
SOUTHWEST AS IT ROUNDS THE AXIS OF THE STEERING STR. 18P IS FORECAST 
TO TRACK SOUTHWESTWARD FROM TAU 12 THROUGH THE END OF THE
FORECAST AT TAU 36 AS IT SHALLOWS OUT AND COMES UNDER THE STEERING 
INFLUENCE OF THE LOW-LEVEL EASTERLY FLOW ALONG THE NORTH SIDE OF A 
RIDGE POSITIONED IN THE TASMAN SEA. REGARDING INTENSITY, 18P IS 
FORECASTED TO CURRENTLY BE AT ITS PEAK INTENSITY OF 55 KTS, AND IS 
EXPECTED TO BEGIN A TERMINAL WEAKENING TREND IMMINENTLY. AS 18P TRACKS 
FARTHER SOUTH, IT WILL ENCOUNTER INCREASINGLY UNFAVORABLE CONDITIONS: 
35-40 KTS OF VWS, MARGINAL (26 C) SSTS, DRY AIR ENTRAINMENT, AND THE 
LOSS OF THE ROBUST OUTFLOW SUPPORT FROM THE UPPER LEVEL TROUGH, ALL BY
TAU 24. CONSEQUENTLY, 18P WILL QUICKLY WEAKEN FROM TAU 12 ONWARD,
AND BEGIN SUBTROPICAL TRANSITION (STT) WHILE IT MOVES POLEWARD.
ULTIMATELY, DISSIPATION IS FORECAST TO OCCUR BEFORE TC 18P
COMPLETES STT, NO LATER THAN TAU 36. 

MODEL DISCUSSION: DETERMINISTIC TRACK MODEL GUIDANCE IS IN GOOD
AGREEMENT IN A SOUTH TO SOUTHWESTWARD TRACK THROUGH TAU 36, WITH
ONLY MINOR DISCREPANCIES IN CROSS-TRACK AND ALONG-TRACK SPREAD. AS
A RESULT, THE JTWC TRACK FORECAST IS PLACED WITH OVERALL HIGH
CONFIDENCE. RELIABLE INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT
18P HAS PEAKED AND WILL BEGIN TERMINALLY WEAKENING IMMINENTLY. ALL
INTENSITY GUIDANCE INDICATES DISSIPATION BY TAU 36 AT THE LATEST,
SUPPORTING THE JTWC INTENSITY FORECAST WITH HIGH CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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