WDXS32 PGTW 052100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (VINCE)      
WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.8S 83.9E
   INITIAL INTENSITY: 110 KTS
   GEOGRAPHIC REFERENCE: 1505 NM EAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 39 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT, 
SYMMETRIC CORE OF DEEP CONVECTION, APPROXIMATELY 120NM DIAMETER, WITH 
A SMALL EYE EVIDENT. EIR IMAGERY INDICATES SIGNIFICANT TROCHOIDAL 
MOTION, WITH DEEP CONVECTION CYCLING RAPIDLY. A 051554Z NOAA-19 MHS 
89GHZ MICROWAVE IMAGE REVEALS A DEFINED MICROWAVE EYE FEATURE, WITH 
THE BULK OF THE DEEP CONVECTION LOCATED OVER THE WESTERN SEMICIRCLE 
AND A BREAK IN THE EYEWALL OVER THE SOUTHEAST QUADRANT. DUE TO 
PARALLAX ERROR AND THE TROCHOIDAL MOTION, THE INITIAL POSITION IS 
PLACED WITH MEDIUM CONFIDENCE BASED PRIMARILY ON THE MHS IMAGE. IN 
GENERAL, ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE, WITH MODERATE 
RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR. DUE TO THE COMPACT NATURE 
OF THE SYSTEM, RAPID FLUCTUATIONS IN THE INTENSITY AND CONVECTIVE 
STRUCTURE CONTINUE UNABATED. THE INITIAL INTENSITY OF 110 KTS IS 
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SUBJECTIVE DVORAK 
ESTIMATES RANGING FROM 102-115 KNOTS. CIMSS OBJECTIVE ESTIMATES SHOW 
A SIMILAR SPREAD FROM 106-112 KNOTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE SOUTHEAST, WITH A BREAK TO THE SOUTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   FMEE: T5.5 - 102 KTS
   CIMSS SATCON: 108 KTS AT 051900Z
   CIMSS ADT: 112 KTS AT 051800Z
   CIMSS AIDT: 106 KTS AT 051800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: MODERATE RADIAL

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 13S HAS SLOWED SLIGHTLY
DUE TO THE WEAKENED STR AND PASSING MAJOR SHORTWAVE TROUGH BUT HAS
CONTINUED WESTWARD. A SHORT-LIVED DIP OR TURN WEST-SOUTHWESTWARD IS
POSSIBLE THROUGH TAU 24. HOWEVER, THE SHORTWAVE TROUGH IS FORECAST
TO QUICKLY PROPAGATE EASTWARD, ALLOWING THE STR TO RE-BUILD TO THE
SOUTH. THIS WILL ACCELERATE THE SYSTEM WESTWARD TO WEST-SOUTHWESTWARD 
THROUGH TAU 72 ALONG THE NORTHERN PERIPHERY OF THE STR. TC 13S WILL 
WEAKEN GRADUALLY THROUGH TAU 36 BUT IS EXPECTED TO REINTENSIFY FROM 
TAU 36 TO TAU 72 AS POLEWARD OUTFLOW IMPROVES INTO THE MIDLATITUDE 
WESTERLIES. AFTER TAU 72, THE STEERING RIDGE WILL RE-ORIENT NORTH-
SOUTH, WITH A BROAD UPPER-LEVEL SUBTROPICAL TROUGH DIGGING 
EQUATORWARD AND ENVELOPING THE SYSTEM, WHICH WILL DRIVE THE SYSTEM 
SOUTHWARD THROUGH TAU 120. ENVIRONMENTAL CONDITIONS WILL DEGRADE IN 
THE EXTENDED PERIOD LEADING TO A PRONOUNCED WEAKENING TREND, WITH 
INCREASING (30-35 KNOTS) VERTICAL WIND SHEAR AND COOLING SST VALUES 
(25-26C).     

MODEL DISCUSSION: GLOBAL MODEL GUIDANCE REMAINS IN GOOD AGREEMENT
THROUGH THE FORECAST PERIOD, WITH A 50NM TO 80NM CROSS-TRACK SPREAD
FROM TAU 72 TO TAU 120. EPS AND GEFS ENSEMBLE GUIDANCE SHOWS A
SLIGHTLY WIDER SPREAD OF SOLUTIONS BUT REMAINS IN OVERALL GOOD
AGREEMENT LENDING HIGH CONFIDENCE TO THE JTWC FORECAST. RELIABLE
INTENSITY GUIDANCE REMAINS IN FAIR AGREEMENT ALTHOUGH THERE IS
SIGNIFICANT UNCERTAINTY IN THE INTENSITY FORECAST DUE TO THE COMPACT 
NATURE OF THE SYSTEM AND THE TENDENCY FOR THESE SYSTEMS TO FLUCTUATE 
QUICKLY.    

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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