WDXS32 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (VINCE) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.0S 68.3E
   INITIAL INTENSITY: 95 KTS
   GEOGRAPHIC REFERENCE: 638 NM EAST-SOUTHEAST OF PORT LOUIS,
MAURITIUS
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 40 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 13S (VINCE) WITH AN ERODING EYEWALL AND WARMING CLOUD TOPS,
PARTICULARLY IN THE NORTHERN SEMICIRCLE. NORTHWESTERLY SHEAR IS
EVIDENT AND IS THE MAIN CULPRIT FOR THE DEFORMATION. A 100055Z
RCM-1 SAR IMAGE REVEALED A VMAX OF 110 KTS LOCALIZED TO THE
SOUTHWESTERN PERIPHERY AND 98-101 KTS WITHIN THE OTHER QUADRANTS.
THE INITIAL INTENSITY IS PLACED WITH MEDIUM CONFIDENCE BASED ON
WEAKENING FROM THE SAR IMAGE AND THE INTENSITY ESTIMATES LISTED
BELOW. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
THE EYE IN ANIMATED MSI AND EXTRAPOLATION FROM THE 100444Z ASCAT-B
IMAGE. ENVIRONMENTAL ANALYSIS INDICATES THAT 13S IS IN A MARGINALLY
FAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG RADIAL OUTFLOW ALOFT,
LOW TO MODERATE (15-20 KTS) NORTHERLY VERTICAL WIND SHEAR, AND WARM
(26-27 C) SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: SAR DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) POSITIONED TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T5.5 - 102 KTS
   FMEE: T5.5 - 102 KTS
   FIMP: T5.0 - 90 KTS
   CIMSS ADT: 99 KTS AT 100600Z
   CIMSS AIDT: 92 KTS AT 100600Z
   CISMS DPRINT: 89 KTS AT 100600Z

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: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: EXTRATROPICAL TRANSITION VICE
SUBTROPICAL TRANSITION TYPE. 

FORECAST DISCUSSION: TC 13S IS FORECAST TO CONTINUE TRACKING
GENERALLY SOUTHWARD, ALONG THE WESTERN PERIPHERY OF THE STR THROUGH
TAU 36. AFTER TAU 36, THE SYSTEM WILL TURN SOUTHEASTWARD AS IT
ROUNDS THE RIDGE AXIS AND ACCELERATES TOWARD THE BAROCLINIC ZONE.
EXTRATROPICAL TRANSITION IS NOW THE FORECAST TRANSITION TYPE DUE TO
THE QUICK ONSET AFTER TAU 48. A SHARP LONG WAVE TROUGH WILL CAUSE
THE SYSTEM TO COMPLETE EXTRATROPICAL TRANSITION NO LATER THAN TAU
72, POSSIBLY TAU 60. REGARDING INTENSITY, 13S IS FORECAST TO
CONTINUE WEAKENING IN RESPONSE TO COOLING SEA SURFACE TEMPERATURES
AND INCREASING VERTICAL WIND SHEAR. SHEAR WILL RISE TO ABOVE 40 KTS
AT TAU 36 AND SEA SURFACE TEMPERATURES DROP TO BELOW 25 C AROUND
THAT SAME TIME. AS A RESULT, INTENSITY IS EXPECTED TO DROP TO
AROUND 50 KTS AT TAU 48. AFTER TAU 48, THE WEAKENING TREND LESSENS
DUE TO BAROCLINIC FORCING.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN VERY GOOD
AGREEMENT THROUGH TAU 48 WITH A 63 NM CROSS-TRACK SPREAD AT THAT
TIME. AFTER TAU 48, ALONG-TRACK SPREAD INCREASES AS THE VORTEX
BEGINS TO INTERACT WITH THE JET MAX TO THE SOUTH. OVERALL, THE JTWC
TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE. INTENSITY GUIDANCE
IS ALSO IN GOOD AGREEMENT WITH ALL MODELS SUGGESTING A SIMILAR RATE
OF WEAKENING. THE JTWC INTENSITY FORECAST IS PLACED WITH HIGH
CONFIDENCE AS WELL.

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