WDXS32 PGTW 090900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (VINCE) WARNING NR 
016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.6S 70.0E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 715 NM EAST OF PORT LOUIS, MAURITIUS
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 45 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT
TROPICAL CYCLONE (TC), WITH AN INNER-CORE STRUCTURE MEASURING
APPROXIMATELY 120NM ACROSS. ENHANCED INFRARED (EIR) SATELLITE
IMAGERY INDICATES THE EYE HAS BROADENED SIGNIFICANTLY OVER THE
PAST 12 HOURS OR SO, NOW UP TO NEARLY 40NM ACROSS. A SERIES OF
89GHZ MICROWAVE IMAGES OVER THE PAST DAY, AS WELL AS THE CIMSS
MIMIC-TC ANIMATION AND M-PERC HOVMOLLER DIAGRAM STRONGLY SUGGEST
THE SYSTEM COMPLETED AN EYEWALL REPLACEMENT CYCLE OVER THE LAST 12
HOURS AND EXPLAIN THE SIGNIFICANT BROADENING OF THE EYE. A 090415Z
AMSU-B 89GHZ MICROWAVE IMAGE DEPICTS AN INCREASINGLY ASYMMETRIC
INNER-CORE, WITH THE EYEWALL BEING QUITE THIN TO THE NORTH, AND
MUCH WIDER TO THE SOUTHEASTERN SIDE. COINCIDENT S1A AND RCM-1
PASSES AT 090049Z AND 090046Z RESPECTIVELY, SHOWED VMAX OF BETWEEN
105-117 KNOTS AND SUPPORTED A DOWNGRADE OF THE 0000Z INTENSITY TO
110 KNOTS. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE
BASED ON THE 39NM WIDE EYE IN THE EIR IMAGERY. THE INITIAL
INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE BULK OF THE
AGENCY FIXES NOTED ABOVE AT T5.5 (102 KNOTS) AND THE CONTINUING
WEAKENING TREND EVIDENCED BY THE EARLIER SAR DATA. THE ENVIRONMENT
REMAINS MARGINAL, WITH LOW DEEP-LAYER SHEAR (MID-LEVEL SHEAR IS
RUNNING FROM THE WEST AT ABOUT 20 KNOTS), WARMS SSTS, AND GOOD
RADIAL AND POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF AN EAST-WEST
ORIENTED EXTENSION OF THE SUBTROPICAL RIDGE (STR) SITUATED TO THE
SOUTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   DEMS: T5.5 - 102 KTS
   FMEE: T5.5 - 102 KTS
   FIMP: T6.0 - 115 KTS
   CIMSS SATCON: 106 KTS AT 090430Z
   CIMSS ADT: 112 KTS AT 090530Z
   CIMSS AIDT: 114 KTS AT 090530Z
   CIMSS D-PRINT: 95 KTS AT 090530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG RADIAL
   OTHER FACTORS: POLEWARD OUTFLOW CHANNEL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 (VINCE) WILL CONTINUE TO TRACK WESTWARD
FOR ANOTHER 12 HOURS OR SO, ALONG AN EAST-WEST ORIENTED EXTENSION
OF THE STR WHICH ITSELF IS POSITIONED FURTHER TO THE SOUTHEAST. THE
RAPID DEVELOPMENT AND DEEPENING OF A DEEP UPPER-LEVEL HEIGHT CENTER
SOUTH OF THE MASCARENES WILL QUICKLY ERODE THE RIDGE EXTENSION
WHILE THE STR CENTER ITSELF SHIFTS NORTHWARD AND REORIENTS TO A
MORE NORTH-SOUTH AXIS. THESE CHANGES IN THE DEEP-LAYER PATTERN WILL
OPEN UP A CLEAR PATH POLEWARD FOR TC 13S TO DRIVE TOWARDS. THE TURN
WILL BE RELATIVELY SLOW DURING THE FIRST 24 HOURS OF THE FORECAST,
BUT THE SYSTEM WILL QUICKLY ACCELERATE AS IT ROUNDS THE AXIS OF THE
RIDGE BY TAU 36. IN TERMS OF INTENSITY, WHILE VINCE HAS COMPLETED
AN EWRC, IT IS UNLIKELY TO BE ABLE TO REINTENSIFY OR SEE A
REDUCTION IN THE EYE SIZE DUE TO IT MOVING OVER STEADILY COOLER
WATERS, A CONSISTENT INCREASE IN DEEP-LAYER SHEAR AND DECREASING
MOISTURE CONTENT. THE FORECAST CALLS FOR RELATIVELY SLOW WEAKENING
THROUGH TAU 36 AS THE STRONG POLEWARD OUTFLOW WILL OFFSET THE 
OTHERWISE NEGATIVE ENVIRONMENTAL EFFECTS FOR A TIME. BY TAU 48, THE
INTENSITY WILL DROP OFF PRECIPITOUSLY, AS THE SYSTEM MOVES SOUTH OF
THE 26C ISOTHERM, SHEAR INCREASES TO MORE THAN 40 KNOTS, AND VERY
DRY MID-LEVEL AIR MOVES IN AND ENGULFS THE SYSTEM. THIS ALSO MARKS
THE BEGINNING OF SUBTROPICAL TRANSITION (STT). THE REMNANTS OF TC
13S WILL COMPLETE STT BY OR SHORTLY AFTER TAU 72 AS IT RACES
SOUTHEASTWARD AND CONTINUES TO RAPIDLY WEAKEN. EXTRATROPICAL
TRANSITION (ETT) IS LIKELY BUT NOT UNTIL WELL AFTER TAU 96 AND
SOUTH OF 40S. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT, WITH A GRADUALLY EXPANDING ENVELOPE REACHING
APPROXIMATELY 100NM BY TAU 72. ALONG-TRACK SPREAD INCREASES AS
EXPECTED AFTER THE SYSTEM ROUNDS THE RIDGE AXIS, OPENING UP TO
ABOUT 165NM BY THE END OF THE FORECAST PERIOD. THE JTWC FORECAST
REMAINS CONSISTENT WITH THE PREVIOUS FORECAST AND IS SITUATED NEAR
TO, BUT FASTER THAN, THE MULTI-MODEL CONSENSUS MEAN. INTENSITY
GUIDANCE IS IN VERY CLOSE AGREEMENT AND THE JTWC FORECAST HUGS THE
CONSENSUS MEAN WITH HIGH CONFIDENCE. 

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