WDPN31 PGTW 281500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.5N 143.7E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 511 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS SPIRAL
CLOUD BANDS AND FLARING CONVECTION WRAPPING INTO A LOW-LEVEL
CIRCULATION CENTER (LLCC) OVER TROPICAL STORM (TS) 12W. THE LLCC
HAS BECOME BROAD AS THE SYSTEM HAS WEAKENED OVER THE LAST SIX
HOURS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON
AN EARLIER 281200Z METOP-C ASCAT IMAGE REVEALING A BULLSEYE
LOW-LEVEL CIRCULATION CENTER. THE INITIAL INTENSITY OF 60 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AFOREMENTIONED
SCATTEROMETRY AND THE FIXES LISTED BELOW. THE CONFIDENCE IS
SLIGHTLY DECREASED IN THE INTENSITY DUE TO A MAXIMUM OF 45KTS
REPRESENTED IN THE NORTHERN PERIPHERY OF THE AFOREMENTIONED
SCATTEROMETRY.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: A COMPETING STEERING ENVIRONMENT
BETWEEN A SUBTROPICAL RIDGE TO THE NORTHWEST AND A NEAR EQUATORIAL
RIDGE TO THE SOUTHEAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.5 - 77 KTS
   RCTP: T4.5 - 77 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 66 KTS AT 281129Z
   CIMSS ADT: 55 KTS AT 281130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD AND EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE TRACK SPEED DECREASES BETWEEN TAU
12-96, RESULTING IN A LONGER QUASI-STATIONARY PERIOD. THE INTENSITY
IS LOWER AS WELL RESULTING FROM SIGNIFICANT UPWELLING AS THE SYSTEM
REMAINS QUASI-STATIONARY.

FORECAST DISCUSSION: TS 12W WILL CONTINUE TRACKING NORTHWESTWARD
WEAKLY THROUGH TAU 12 WHILE REMAINING IN A COMPETING STEERING
ENVIRONMENT. AFTER TAU 12, THE RIDGE TO THE NORTHWEST BUILDS,
SLOWING THE TRACK SPEED SIGNIFICANTLY. AS A RESULT, TS 12W IS
EXPECTED TO TRACK IRREGULARLY IN A QUASI-STATIONARY PERIOD. THE
NORTHWESTERN RIDGE WILL GRADUALLY WEAKEN AFTER TAU 72, AND THE
SOUTHEASTERN RIDGE WILL TRACK TS 12W NORTH-NORTHEASTWARD THROUGH
THE REMAINDER OF THE FORECAST PERIOD. DRY AIR TO THE NORTHWEST
ASSOCIATED WITH THE DEEP-LAYER RIDGE AND SIGNIFICANT UPWELLING WILL
CONTINUE TO ENTRAIN INTO THE LLCC FOR THE NEXT 72 HOURS. THE SYSTEM
WILL MOVE INTO WARMER WATERS AFTER TAU 72, RESULTING IN SLIGHT
REINTENSIFICATION IN A MARGINAL ENVIRONMENT WITH MODERATE VERTICAL
WIND SHEAR AND MARGINAL UPPER-LEVEL DIVERGENCE TO A PEAK OF 60KTS.

MODEL DISCUSSION: TS 12W IS IN STRONG AGREEMENT OVER THE NEXT 12
HOURS, BUT STRONGLY BIFURCATES AFTER TAU 12. THE CROSS-TRACK SPREAD
IS APPROXIMATELY 100NM BY THE END OF THE FORECAST PERIOD. THE
INTENSITY GUIDANCE FOLLOWS IN SUIT AND IS HIGHLY VARIABLE BASED ON
THE DIRECTION THAT THE SYSTEM TRACKS. DIFFERENT MODEL FIELDS REVEAL
A VARIETY OF MODEL FIELD SOLUTIONS BETWEEN VERTICAL WIND SHEAR,
RELATIVE HUMIDITY, AND UPPER-LEVEL DIVERGENCE.

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