WDXS31 PGTW 030300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 14S (VERNON) WARNING 
NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.4S 82.7E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 146 NM SOUTHEAST OF DIEGO GARCIA
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS RAGGED
CONVECTION HAS FLARED CONTINUOUSLY WITH CLOUD TOPS IN A WARMING
PHASE. A 032300Z SSMIS 89GHZ MICROWAVE IMAGE SHOWED THE RAGGED LLCC
WITH THE MAJORITY OF THE  CONVECTIVE ACTIVITY DISPLACED FROM CENTER
TO THE SOUTH, WITH WEAK LOW LEVEL BANDING FEATURES ON THE NORTH
SIDE THE CIRCULATION, PROVIDING HIGH CONFIDENCE TO THE INITIAL
POSITION. THE INITIAL INTENSITY OF 50 KNOTS IS BASED ON AN OVERALL
ASSESSMENT OF AGENCY AND AUTOMATED DVORAK ESTIMATES AND REFLECTS
THE SUSTAINED 6-HR EIR CONVECTIVE STRUCTURE. GEOSTATIONARY WATER
VAPOR IMAGERY SUGGESTS A WEDGE OF DRY AIR CONTINUED TO WRAP IN
CLOSER TO THE CORE FROM THE NORTHEAST. CIMSS VWS ANALYSIS REVEALS
THE SYSTEM IS MOVING INTO 20-25 KNOTS OF PERSISTENT SHEAR. THE
ENVIRONMENT IS MARGINAL WITH WARM SSTS AND ROBUST POLEWARD OUTFLOW
OFFSET BY INCREASING VWS AND INFLUX OF DRY AIR. THE CYCLONE IS
TRACKING ALONG THE NORTHWEST PERIPHERY OF THE STR TO THE SOUTHEAST

INITIAL WIND RADII BASIS: PERSISTENCE FROM A BULLSEYE ASCAT PASS AT
021636Z.

CURRENT STEERING MECHANISM: NORTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   CIMSS SATCON: 57 KTS AT 021954Z
   CIMSS ADT: 55 KTS AT 022115Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 14S WILL CONTINUE TRACKING SOUTH-SOUTHWEST
FOR THE NEXT 24 TO 48 HOURS, ALONG THE NORTHWESTERN PERIPHERY OF
THE STEERING RIDGE TO THE SOUTHEAST IN THE DIRECTION OF A WEAKNESS
IN THE RIDGE INDUCED BY THE APPROACH OF A MID-LATITUDE TROUGH. THE
SYSTEM WILL TURN MORE SOUTHWARD BY TAU 48. 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 HOURS, BUT THEN BEGIN A STEADY WEAKENING TREND AS THE SHEAR
INCREASES AND SSTS BEGIN TO DECREASE BY TAU 48 WHILE THE SYSTEM
BEGINS SUBTROPICAL TRANSITION BY TAU 60. TC 14S WILL COMPLETE
TRANSITION INTO A STRONG GALE-FORCE SUBTROPICAL LOW NO LATER THAN
TAU 72.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL VERY GOOD
AGREEMENT THROUGH THE FORECAST PERIOD, WITH LESS CONFIDENCE BY
AFTER TAU 48 WITH A GRADUAL SPREAD TO 180 NM BY TAU 72. THE TRACK
LIES ON THE WESTERN SIDE OF THE CONSENSUS WITH HIGH CONFIDENCE. THE
INTENSITY FORECAST LIES NEAR THE CONSENSUS MEAN THROUGH THE
FORECAST PERIOD. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, WITH
A PEAK OF 55 KNOT PEAK BY TAU 12 FOLLOWED BY A STEADY WEAKENING
TREND THEREAFTER. 

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