WDPN31 PGTW 031500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
044//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 41.2N 157.5E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 741 NM EAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 24 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A SYSTEM
IN THE THROES OF RAPID VORTEX DECOUPLING, WITH A PARTIALLY EXPOSED
LOW LEVEL CIRCULATION CENTER (LLCC) SOUTHWEST OF THE MID-LEVEL
ROTATION WITH REMNANT CONVECTION. A 031049Z ASCAT-B AND A 030952Z
ASCAT-C PASS REVEALED A SMALL LLCC WITH A BROAD SWATH OF GALE-FORCE
WINDS ACROSS THE SOUTHERN HEMISPHERE OF THE CIRCULATION AND AN
EMBEDDED REGION OF 45-50 KNOT WINDS TO THE SOUTH. THE SERIES OF
ASCAT PASSES LENT HIGH CONFIDENCE TO THE INITIAL POSITION. THE
SCATTEROMETER DATA ALSO PROVIDED HIGH CONFIDENCE TO THE INITIAL
INTENSITY, WHICH WAS HELD HIGHER THAN THE SUBJECTIVE AND OBJECTIVE
ESTIMATES NOTED BELOW DUE TO THE SCATTEROMETER DATA. ENVIRONMENTAL
CONDITIONS ARE RAPIDLY BECOMING UNFAVORABLE, WITH STRONG WESTERLY
SHEAR, VERY COOL SSTS, AND SIGNIFICANT DRY AIR, PARTICULARLY ALONG
THE WESTERN FLANK, OFFSET BY ROBUST POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: VORTEX DECOUPLING.

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.0 - 30 KTS
   KNES: T2.5 - 35 KTS
   CIMSS ADT: 41 KTS AT 031140Z
   CIMSS AIDT: 45 KTS AT 031140Z
   CIMSS D-MINT: 38 KTS AT 030752Z
   CIMSS D-PRINT: 40 KTS AT 031230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 20-22 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: TROPICAL STORM (TS) 12W IS MOVING QUICKLY NOW,
ALONG THE NORTHERN SIDE OF THE STRONG RIDGE TO THE SOUTH. WHILE
THIS RIDGE WILL QUICKLY MOVE SOUTHWEST OVER THE NEXT 12 TO 24
HOURS, THERE WILL BE LITTLE IMPACT ON EITHER THE TRACK SPEED OR
DIRECTION DUE TO THE FACT THAT ANOTHER RIDGE QUICKLY MOVES IN FROM
THE EAST AND THE STEERING HANDOFF WILL BE QUITE RAPID. TS 12W IS
THUS EXPECTED TO CONTINUE TRACKING EAST-NORTHEASTWARD AT ABOUT
22-24 KNOTS THROUGH THE ENTIRE FORECAST PERIOD. AS TS 12W BECOMES
FULLY DECOUPLED, MOVES OVER EVEN COLDER WATERS AND DRY AIR RUSHES
TO ENGULF THE REMNANT VORTEX, IT WILL STEADILY WEAKEN WHILE
SIMULTANEOUSLY UNDERGOING EXTRATROPICAL TRANSITION (ETT).
COMPLETION OF ETT IS ANTICIPATED BY TAU 36. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE DISPLAYS LITTLE IN
THE WAY OF EITHER CROSS- OR ALONG-TRACK SPREAD THROUGH THE FORECAST
PERIOD, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST. INTENSITY
GUIDANCE IS ALSO IN GOOD AGREEMENT ON A STEADY WEAKENING THROUGH
ETT, THOUGH THE MAJORITY OF THE GUIDANCE IS A BIT TOO QUICK TO
DISSIPATE THE SOON TO BE EXTRATROPICAL LOW AND THE JTWC FORECAST IS
HEDGED SLIGHTLY HIGHER TO REFLECT THAT. 

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