WDXS32 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (VINCE)        
WARNING NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.2S 88.0E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 1741 NM EAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 35 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT 
SYSTEM, WITH A RAGGED, INCONSISTENT EYE, WHICH SUPPORTS THE INITIAL 
POSITION WITH HIGH CONFIDENCE. DUE TO THE COMPACT NATURE OF THE SYSTEM, 
THE CIMSS OBJECTIVE INTENSITY ESTIMATES REMAIN TOO LOW, RANGING FROM 61-
77 KNOTS. ANIMATED WATER VAPOR IMAGERY INDICATES A GENERALLY FAVORABLE 
ENVIRONMENT, WITH MODERATE POLEWARD OUTFLOW AND WARM SST VALUES (26-
27C). HOWEVER, NORTHEASTERLY VERTICAL WIND SHEAR IS CLEARLY IMPINGING ON 
THE NORTHEAST QUADRANT OF THE SYSTEM AS EVIDENCED IN THE 041607Z MHS 
89GHZ MICROWAVE IMAGE, WHICH SHOWS A BREAK IN THE EYEWALL AND WEAKER 
DEEP CONVECTIVE BANDING. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM 
CONFIDENCE BASED ON THE HIGHER END OF THE DVORAK CURRENT INTENSITY 
ESTIMATES RANGING FROM 77-102 KNOTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   FMEE: T4.5 - 77 KTS
   CIMSS SATCON: 77 KTS AT 041815Z
   CIMSS ADT: 61 KTS AT 041815Z
   CIMSS AIDT: 67 KTS AT 041815Z
   CIMSS D-PRINT: 74 KTS AT 041815Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 IS FORECAST TO TRACK
WEST-SOUTHWESTWARD THROUGH TAU 96 ALONG THE NORTHWESTERN PERIPHERY
OF THE STR. A SLIGHT, SHORT-LIVED DIP IS POSSIBLE IN THE TRACK FROM
TAU 24 TO TAU 36 AS A MIDLATITUDE SHORTWAVE TROUGH PASSES WELL TO
THE SOUTH. HOWEVER, THE STR WILL RE-BUILD DRIVING THE SYSTEM
WEST-SOUTHWESTWARD UNTIL A MAJOR SHORTWAVE TROUGH APPROACHES AND
RECURVES THE SYSTEM SOUTHWESTWARD AROUND THE NORTHWEST PERIPHERY OF
THE STR. TC 13S SHOULD WEAKEN SLIGHTLY OVER THE NEXT DAY, WITH
RE-INTENSIFICATION ANTICIPATED AFTER TAU 72 AS POLEWARD OUTFLOW
IMPROVES INTO THE MIDLATITUDE WESTERLIES.   

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT, WITH A 55NM CROSS-TRACK SPREAD AT TAU 96, DIVERGING TO
110NM BY TAU 120 WHEN THE SYSTEM BEGINS ITS RECURVE. PROBABILISTIC
GUIDANCE IS IN GOOD AGREEMENT THROUGH THE FORECAST PERIOD LENDING
HIGH CONFIDENCE TO THE JTWC FORECAST TRACK. THE INTENSITY FORECAST
REMAINS CHALLENGING, DUE IN LARGE PART TO THE COMPACT STRUCTURE OF
THE SYSTEM AND THE LARGE SPREAD IN RELIABLE INTENSITY GUIDANCE.
HAFS-A SHOWS A WEAKENING TREND THROUGH TAU 36 TO ABOUT 83 KNOTS
THEN A STEADY RE-INTENSIFICATION TO 103 KNOTS BY TAU 108. COAMPS-TC
(GFS), ON THE OTHER HAND, IS ERRATIC AND UNLIKELY SHOWING A RAPID
WEAKENING TREND TO 60 KNOTS THEN FLAT TREND THROUGH TAU 120.    

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