WDPN31 PGTW 030900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
043//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 40.5N 154.5E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 607 NM EAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 25 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY
DECOUPLING SYSTEM, WITH THE WESTERN PORTIONS OF THE LOW LEVEL
VORTEX STARTING PEAK OUT FROM UNDER MID-LEVEL CONVECTION BEING
SHEARED OFF THE NORTHEAST. A 030738Z WSF-M COLOR-ENHANCED 89GHZ
MICROWAVE IMAGE CONFIRMS THE VORTEX DECOUPLING PROCESS HAS BEGUN,
AS SOUTHWESTERLY SHEAR NOW EXCEEDS 25 KNOTS. THE INITIAL POSITION
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LOW
LEVEL CIRCULATION CENTER (LLCC) IN THE MSI. THE INITIAL INTENSITY
IS ASSESSED WITH HIGH CONFIDENCE, HEDGED HIGHER THAN THE BULK OF
THE OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES IN LIGHT OF A
030017Z ASCAT-C PASS THAT SHOWED A PERSISTENT AREA OF 50-55 KNOT
WINDS IN THE SOUTHEASTERN QUADRANT. ENVIRONMENTAL CONDITIONS ARE
DETERIORATING RAPIDLY AS THE SHEAR HAS NOW BEGUN TO TAKE EFFECT.
COOL SSTS AND DRY AIR INTRUSION ARE COMPOUNDING THE IMPACT OF THE
SHEAR AND ARE OFFSETTING THE CONTINUED ROBUST POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 45 KTS AT 030530Z
   CIMSS AIDT: 43 KTS AT 030730Z
   CIMSS D-PRINT: 39 KTS AT 030700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 22-23 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY MID-LEVEL AIR ACROSS THE WESTERN
AND SOUTHWESTERN PORTIONS OF THE CIRCULATION. 

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. THE FORECAST HAS BEEN
SHORTENED TO 36 HOURS. 

FORECAST DISCUSSION: TROPICAL STORM (TS) 12W WILL TRACK
EAST-NORTHEASTWARD ALONG THE NORTHERN PORTION OF THE STEERING RIDGE
FOR THE DURATION OF THE FORECAST PERIOD. A GRADUAL SLOWING OF TRACK
SPEEDS IS EXPECTED AFTER TAU 24 AS THE PRIMARY STEERING INFLUENCE
SHIFTS FROM THE STR TO THE SOUTH, TO ANOTHER STR MOVING IN FROM THE
EAST. THE SYSTEM WILL STEADILY WEAKEN UNDER UNFAVORABLE
ENVIRONMENTAL CONDITIONS INCLUDING HIGH SHEAR, COOL SSTS AND DRY
AIR ENTRAINMENT, THROUGH THE FORECAST PERIOD. EXTRATROPICAL
TRANSITION (ETT) IS SET TO BEGIN WITHIN THE NEXT 24 HOURS AND
RAPIDLY COMPLETE AS THE SYSTEM DEVELOPS FRONTAL CHARACTERISTICS AND
IS PICKED UP BY A MID-LATITUDE MAJOR SHORTWAVE TROF. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN STRONG
AGREEMENT WITH MINIMAL CROSS- OR ALONG-TRACK SPREAD THROUGH THE
FORECAST PERIOD, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST
TRACK. INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT, SHOWING STEADY
WEAKENING THROUGH ETT. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: HIGH//
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