WDXS31 PGTW 011500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 14S (VERNON) WARNING 
NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.8S 85.6E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 963 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS AN AREA
OF PERSISTENT, SYMMETRICAL CONVECTION WITH A FEW OVERSHOOTING TOPS,
OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). WHILE THE
CONVECTION AND OVERSHOOTING TOPS LOOK RATHER OMINOUS, A SERIES OF
37GHZ MICROWAVE IMAGES INCLUDING A 010753Z AMSR2, A 010929Z GMI AND
A 011047Z SSMIS, CONFIRM THAT THE LLCC IS DISPLACED TO THE
NORTHEAST OF THE CENTER OF THE CONVECTION DUE TO PERSISTENT
MODERATE NORTHEAST SHEAR. THE SERIES OF MICROWAVE IMAGES PROVIDED
HIGH CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY OF
45 KNOTS IS ASSESSED WITH HIGH CONFIDENCE, BASED ON A CONGRUENCE OF
AGENCY SUBJECTIVE AND AUTOMATED OBJECTIVE FIXES. ANALYSIS REVEALS A
SOMEWHAT MARGINAL ENVIRONMENT WITH WARM SSTS AND STRONG POLEWARD,
DIVERGENT OUTFLOW OFFSET BY MID-LEVEL DRY AIR ENTRAINMENT AND
MODERATE SHEAR. CIMSS SHEAR ANALYSIS INDICATES 5-10 KNOTS OF SHEAR,
WHILE HWRF MODEL DERIVED SOUNDINGS AND SHIPS GUIDANCE INDICATE MORE
MODERATE VALUES BETWEEN 15-20 KNOTS. BASED ON THE SATELLITE
DEPICTION, THE HIGHER SHEAR VALUES APPEAR A MORE REALISTIC
ASSESSMENT.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   FMEE: T3.5 - 55 KTS
   CIMSS SATCON: 42 KTS AT 010813Z
   CIMSS ADT: 45 KTS AT 010915Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR ENTRAINMENT ALONG THE NORTHERN
PERIPHERY 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 TO TRACK SOUTHWESTWARD
THROUGH THE FORECAST PERIOD, ALONG THE WESTERN SIDE OF A STRONG STR
CENTERED TO THE EAST. AT THE TAIL END OF THE FORECAST, THE SYSTEM
IS EXPECTED TO TURN MORE SOUTHWARD AS IT SLIDES INTO A WEAKNESS IN
THE RIDGE INDUCED BY THE PASSING OF A MAJOR SHORTWAVE TROUGH TO THE
SOUTH. FROM AN INTENSITY PERSPECTIVE, THE ENVIRONMENT IS EXPECTED
TO REMAIN RELATIVELY STEADY, WITH THE STRONG POLEWARD OUTFLOW
CONTINUING TO BE OFFSET BY THE MID-LEVEL DRY AIR AND PERSISTENT
NORTHEASTERLY SHEAR. HOWEVER, SHEAR IS EXPECTED TO WEAKEN SLIGHTLY
OVER THE NEXT 24 HOURS, WHICH SHOULD ALLOW FOR SOME MINOR
INTENSIFICATION, TO A PEAK OF 55 KNOTS BY TAU 24. AFTER THIS POINT,
THE COMBINATION OF INCREASING SHEAR AND MORE SIGNIFICANT
ENTRAINMENT OF DRY AIR WILL MARK THE START OF A SLOW BUT STEADY
WEAKENING TREND. THE SYSTEM WILL CROSS THE 26C SST ISOTHERM AROUND
TAU 48, AND BEGIN INTERACTING WITH A 500M SUBTROPICAL TROUGH, AND
BEGIN SUBTROPICAL TRANSITION. AS THE SYSTEM CONTINUES SLIDING
SOUTHWARD IT WILL MOVE OVER STEADILY DECREASING SSTS, WHILE SHEAR
BUILDS SIGNIFICANTLY AND IT BECOMES ENVELOPED WITHIN A POCKET OF
DRY AIR. BY TAU 96 THE SYSTEM TRANSITIONS TO A SHALLOW WARM CORE,
SUBTROPICAL SYSTEM AS IT MOVES UNDER A 500MB LOW AND 200MB JET
STREAK BUT REMAINS NORTH OF THE LOW LEVEL SUBTROPICAL RIDGE. 

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN
GOOD AGREEMENT WITH A SPREAD OF 135NM BETWEEN THE GFS TO THE WEST
AND EGRR ON THE EAST SIDE OF THE ENVELOPE. MODELS BEGIN TO DIVERGE
BY TAU 906 AS THE SYSTEM UNDERGOES SUBTROPICAL TRANSITION, WITH
CROSS TRACK SPREAD INCREASING TO 250NM BY TAU 96. THE JTWC TRACK
LIES ALONG THE WESTERN SIDE OF THE TRACK ENVELOPE, FAVORING THE
ECMWF SOLUTION FOR THE DURATION OF THE FORECAST, WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN FAIRLY GOOD AGREEMENT,
WITH A FAIRLY TIGHT ENVELOPE WITH A PEAK BETWEEN 45-60 KNOTS
FOLLOWED BY SLOW BUT STEADY WEAKENING THEREAFTER. THE JTWC FORECAST
REMAINS WITHIN THE ENVELOPE, ABOUT FIVE KNOTS LOWER THAN THE
CONSENSUS MEAN THROUGH THE FORECAST PERIOD WITH MEDIUM CONFIDENCE. 

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