WDXS32 PGTW 060900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 13S (VINCE) WARNING NR 
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3S 82.5E
   INITIAL INTENSITY: 105 KTS
   GEOGRAPHIC REFERENCE: 936 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 13S (VINCE) WITH A VERY COMPACT CENTRAL DENSE OVERCAST
(CDO) SURROUNDING THE EYEWALL OF A 15 NM EYE. A 052350Z RCM-2 SAR
WIND SPEED IMAGE SHOWS A VMAX OF 104 KTS LOCALIZED TO A SMALL
PORTION OF THE NORTHWESTERN EYEWALL WITH 90-95 KTS WITHIN THE OTHER
QUADRANTS. THE SYSTEM HAS IMPROVED IN APPEARANCE SINCE THEN,
LEADING TO THE ASSESSMENT OF THE INITIAL INTENSITY AT 105 KTS. DUE
TO SOME OF THE AGENCY DVORAK ESTIMATES BEING A BIT HIGHER, THE
INITIAL INTENSITY IS PLACED MEDIUM CONFIDENCE. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE IN THE ANIMATED
MSI. ENVIRONMENTAL ANALYSIS INDICATES THAT 13S IS IN A FAVORABLE
ENVIRONMENT CHARACTERIZED BY MODERATE RADIAL OUTFLOW ALOFT, LOW
(10-15 KTS) VERTICAL WIND SHEAR, AND WARMISH (26-27 C) SEA SURFACE
TEMPERATURES.

INITIAL WIND RADII BASIS: PERSISTENCE FROM THE MENTIONED SAR DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T6.0 - 115 KTS
   KNES: T6.0 - 115 KTS
   DEMS: T6.0 - 115 KTS
   FMEE: T5.5 - 102 KTS
   CIMSS ADT: 112 KTS AT 060600Z
   CIMSS AIDT: 103 KTS AT 060600Z
   CIMSS DPRINT: 103 KTS AT 060700Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: 13S IS FORECAST TO TRACK WEST-SOUTHWESTWARD,
ALONG THE NORTHWESTERN PERIPHERY OF THE STR THROUGH TAU 72. NEAR
TAU 72, THE SYSTEM WILL BEGIN TO ROUND THE AXIS OF THE RIDGE IN
RESPONSE TO THE REORIENTATION OF THE RIDGE TO A NORTH-SOUTH
ALIGNMENT. 13S WILL CONTINUE ON A SOUTHWARD TRACK THROUGH THE
REMAINDER OF THE FORECAST PERIOD. NEAR TAU 120, THE VORTEX WILL
BEGIN TO INTERACT WITH A BRANCH OF THE JET, MARKING THE TRANSITION
TO A SUBTROPICAL CYCLONE. FULL EXTRATROPICAL TRANSITION IS EXPECTED
TO BE PROLONGED, CAUSING 13S TO LIKELY BE DESIGNATED AS A
SUBTROPICAL CYCLONE SOON AFTER TAU 120. REGARDING INTENSITY, 13S IS
FORECAST TO BASICALLY MAINTAIN INTENSITY OVER THE NEXT 72 HOURS AS
ENVIRONMENTAL PARAMETERS ARE EXPECTED TO REMAIN OVERALL FAVORABLE.
HOWEVER, BORDERLINE SEA SURFACE TEMPERATURES OF AROUND 26 C AND
SLIGHT DRY AIR ENTRAINMENT ARE EXPECTED TO CAP INTENSIFICATION.
AFTER TAU 72, SEA SURFACE TEMPERATURES QUICKLY DROP AND VERTICAL
WIND SHEAR RISES. THESE TWO FACTORS WILL CAUSE 13S TO WEAKEN TO
AROUND 65 KTS AT THE END OF THE FORECAST PERIOD AS THE VORTEX
SHALLOWS OUT AND BEGINS SUBTROPICAL TRANSITION. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT
REGARDING THE TRACK OF 13S WITH A 160 NM CROSS-TRACK SPREAD AT TAU
72. AFTER TAU 72, ALONG-TRACK SPREAD INCREASES AS MODELS DIFFER IN
THE SPEED OF ROUNDING THE RIDGE AXIS. ECMWF IS THE SLOWEST WHILE
GFS IS THE FASTEST. AS A RESULT, THE JTWC TRACK FORECAST IS PLACED
WITH HIGH CONFIDENCE THROUGH TAU 72 AND LOW CONFIDENCE THEREAFTER.
INTENSITY GUIDANCE, WITH THE EXCEPTION OF GFS, IS IN GOOD
AGREEMENT. GFS IS AN OUTLIER, HAVING THE SYSTEM 25 KTS WEAKER
THROUGH TAU 72. ALL MODELS SUGGEST WEAKENING AFTER TAU 72. WITH THE
SYSTEM BEING SMALL, THERE IS ONLY MEDIUM CONFIDENCE IN THE
INTENSITY FORECAST AS SMALL SYSTEMS CAN HIGHLY FLUCTUATE WITH THEIR
INTENSITY. 

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