WDXS32 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (VINCE) WARNING NR 
015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.5S 71.5E
   INITIAL INTENSITY: 115 KTS
   GEOGRAPHIC REFERENCE: 799 NM EAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 50 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS THE EYE OF
TROPICAL CYCLONE (TC) 13S (VINCE) BEGINNING TO COOL AND BECOME MORE
RAGGED IN APPEARANCE. AS 13S IS SURROUNDED BY DRIER AIR, ITS
CONVECTIVE BANDING SIGNATURE IS SHOWING SIGNS OF INTRUSION, WHILE
THE CORE OF THE SYSTEM REMAINS RELATIVELY STRONG. PAIRED WITH
STRONG, RADIAL OUTFLOW, THE ENVIRONMENT IS ANALYZED AS MARGINALLY 
FAVORABLE. SEA SURFACE TEMPERATURES OSCILLATE AROUND 27C, WHILE THE 
VERTICAL WIND SHEAR IS MODERATE AND FAVORABLE (15-20 KTS). THE INITIAL 
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE OBJECTIVE 
ESTIMATES AND AGENCY FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   CIMSS SATCON: 111 KTS AT 081329Z
   CIMSS ADT: 112 KTS AT 081800Z
   CIMSS AIDT: 106 KTS AT 081800Z
   CIMSS D-PRINT: 102 KTS AT 081800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG RADIAL

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: TC 13S IS FORECAST TO CONTINUE TO TRACK ALONG
THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TO THE
SOUTHEAST. IT IS CURRENTLY EXPECTED TO SLOW DOWN OVER THE NEXT 48 
HOURS,
UNTIL IT ROUNDS THE AXIS OF THE RIDGE. JUST PRIOR TO THAT, A
MID-LEVEL TROUGH WILL DEVELOP TO THE SOUTHWEST OF THE PATH OF TC
13S, AND AS SOON AS THE SYSTEM STARTS TRACKING SOUTH, IT WILL START
ACCELERATING POLEWARD. AROUND TAU 72 THE SYSTEM IS EXPECTED TO
BEGIN SUBTROPICAL TRANSITION, AS IT CROSSES INTO AN AREA OF COOLER
SEA SURFACE TEMPERATURES (BELOW 26C) AND DRASTICALLY INCREASING VWS
(45-50 KTS). TC 13S IS EXPECTED TO COMPLETE SUBTROPICAL
TRANSITION BY TAU 96. IN TERMS OF INTENSITY, THE FORECAST CALLS FOR
STEADY, BUT SLOW WEAKENING, OVER THE NEXT 48 HOURS, AS THE
ENVIRONMENT REMAINS MARGINAL TO MARGINALLY FAVORABLE. HOWEVER, PAST
TAU 48, SST, VWS, COMBINED WITH A STRONG DRY AIR INTRUSION FROM
THE WEST WILL BEGIN TO ERODE THE CORE OF THE SYSTEM AND LEAD TO A
MORE RAPID WEAKENING, CULMINATING ON 50 KTS, TOWARDS THE END OF THE
FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL DETERMINISTIC MODEL GUIDANCE IS IN GOOD
AGREEMENT IN REGARD TO THE TRACK, WITH JUST 80 NM CROSS-TRACK
SPREAD AT TAU 48, WITH SIMILAR ALONG-TRACK SPREAD, INDICATING TIGHT
AGREEMENT IN REGARD TO THE RATE OF TURNING, WHILE THE SYSTEM ROUNDS 
THE AXIS OF THE STR. CROSS-TRACK SPREAD INCREASES TO 150 NM BY TAU 72, 
INDICATING INCREASING UNCERTAINTY IN REGARD TO THE TIMELINE AND ANGLE 
OF TURNING DURING THE SUBTROPICAL TRANSITION. HOWEVER, BETWEEN TAUS 72
AND 96, THE CROSS-TRACK SPREAD OF THE GUIDANCE REMAINS NEARLY
CONSTANT. JTWC TRACK FORECAST IS LAID IN CLOSE PROXIMITY TO THE
MULTI-MODEL CONSENSUS. AS FAR AS INTENSITY, ALL MODEL GUIDANCE IS
PREDICTING SIMILAR RATE OF WEAKENING THROUGHOUT THE FORECAST
PERIOD, WITH THE ONLY OUTLIER BEING GFS, WHICH SHOWS A SHARPER
INITIAL WEAKENING, EXTENDING THROUGH TAU 48, AFTER WHICH IT MATCHES
THE MULTI-MODEL CONSENSUS, WHICH THE JTWC FORECAST IS CLOSELY ALIGNED
WITH. 

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