WDXS31 PGTW 021500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 14S (VERNON) WARNING 
NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.3S 83.5E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 973 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A RAGGED
AND RATHER ILL-DEFINED BALL OF CONVECTION DISPLACED TO THE
SOUTHWEST OF AN OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC). OVER
THE PAST TWELVE HOURS, THE CONVECTION HAS CYCLED CONTINUOUSLY AND
AT PRESENT CLOUD TOPS ARE IN A WARMING PHASE. A 021148Z SSMIS 37GHZ
MICROWAVE IMAGE SHOWED THE RAGGED LLCC WITH THE BULK OF CONVECTIVE
ACTIVITY IN A BROAD SWATH TO THE SOUTH, AND ONLY WEAK LOW LEVEL
BANDING FEATURES TO THE NORTH SIDE OF THE CIRCULATION, AND LENT
HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY OF
50 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE, ROUGHLY IN THE MEAN
BETWEEN THE PGTW AND FMEE DVORAK INTENSITY ESTIMATES AND SLIGHTLY
LESS THAN THE ADT AND SATCON. GEOSTATIONARY AND MICROWAVE TPW
IMAGERY SUGGESTS A WEDGE OF DRY AIR IS ENTRENCHED ACROSS THE NORTH
SIDE OF THE SYSTEM, AND BEGINNING TO WRAP IN CLOSER TO THE CORE
FROM THE NORTHEAST. CIMSS VWS ANALYSIS REVEALS 15-20 KNOTS OF
PERSISTENT NORTHERLY SHEAR AND IS BORN OUT BY THE SATELLITE
ANALYSIS. BEYOND THAN THE SHEAR AND DRY AIR, THE ENVIRONMENT IS
OTHERWISE FAVORABLE, WITH WARM SSTS AND ROBUST POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   CIMSS SATCON: 54 KTS AT 020754Z
   CIMSS ADT: 53 KTS AT 020915Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR ENTRAINMENT. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 14S WILL CONTINUE TRACKING SOUTH-SOUTHWEST
FOR THE NEXT 48 HOURS, ALONG THE WESTERN PERIPHERY OF THE STEERING
RIDGE TO THE EAST AND TOWARDS A WEAKNESS IN THE RIDGE PATTERN
INDUCED BY THE APPROACH OF A MID-LATITUDE TROUGH. THE SYSTEM WILL
TURN MORE SOUTHWARD BY THE END OF THE FORECAST AS IT BEGINS TO SLOW
DOWN SLIGHTLY. NO SIGNIFICANT ENVIRONMENTAL CHANGES ARE EXPECTED IN
THE FIRST 36 HOURS OF THE FORECAST, WITH SUPPORTIVE SSTS AND ROBUST
OUTFLOW COMPETING WITH PERSISTENT NORTHERLY SHEAR AND DRY AIR
ENCROACHMENT FROM THE NORTH. THE SYSTEM IS FORECAST TO BRIEFLY
INTENSITY TO 55 KNOTS IN THE NEXT 12 TO 24 HOURS, BUT THEN BEGIN A
STEADY WEAKENING TREND AS THE SHEAR COMES TO DOMINATE OVER THE
OUTFLOW AND SSTS BEGIN TO DROP OFF. THE SYSTEM WILL MOVE INTO
SIGNIFICANTLY COOLER WATERS AROUND TAU 48, AND BEGIN SUBTROPICAL
TRANSITION. AS THE SYSTEM IS ENVELOPED BY DRY AIR, MOVES UNDER A
200MB JET STREAK AND MOVES INTO A REGION OF SUB-23C SSTS, IT WILL
COMPLETE TRANSITION INTO A STRONG GALE-FORCE SUBTROPICAL LOW NO
LATER THAN TAU 72, AND LIKELY AS EARLY AS TAU 60  

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
VERY GOOD AGREEMENT THROUGH THE FORECAST PERIOD, WITH A SPREAD OF
ONLY 150NM AT TAU 72. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT,
WITH A FIVE KNOT SPREAD ABOUT A 50-55 KNOT PEAK BY TAU 12 FOLLOWED
BY SLOW BUT STEADY WEAKENING. THE JTWC TRACK LIKES ON THE WESTERN
SIDE OF THE ENVELOPE WITH HIGH CONFIDENCE. THE INTENSITY FORECAST
LIES NEAR THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD WITH
MEDIUM CONFIDENCE. 

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