WDPN31 PGTW 282100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.0N 143.1E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 215 NM NORTH-NORTHEAST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM (TS) 12W (KROSA) WITH A PARTIALLY EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) AND ASSOCIATED BUT SHORT-LIVED CONVECTION
FLARING IN THE SOUTHEAST QUADRANT. AROUND THE PERIPHERY OF THE
SYSTEM, FRAGMENTED LOW-LEVEL CONVECTIVE BANDING HAS BEEN OBSERVED
WRAPPING NEATLY INTO THE WELL-DEFINED LLCC. ALOFT, WEAK EQUATORWARD
OUTFLOW HAS BEEN IDENTIFIED ON ANIMATED WATER VAPOR IMAGERY,
HOWEVER, DRY AIR IS PREVALENT AND WRAPPING INTO THE SOUTHERN
SEMICIRCLE FROM THE WESTERN FLANK. WITH REGARD TO THE ENVIRONMENTAL
ANALYSIS, LOW VERTICAL WIND SHEAR (LESS THAN 15 KTS) AND WARM SEA
SURFACE TEMPERATURES (26-27 C) CONTINUE TO SUSTAIN THE SYSTEM
THROUGH ITS NORTH-NORTHWEST TRACK. THE INITIAL POSITION HAS BEEN
PLACED WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED PARTIALLY
EXPOSED LLCC. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON AN EARLIER 281159Z METOP-C ASCAT IMAGE AND
AGENCY DVORAK FIX ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: A COMPETING STEERING ENVIRONMENT,
WEDGED BETWEEN A DEEP-LAYER SUBTROPICAL RIDGE LOCATED TO THE EAST
AND A SECOND SUBTROPICAL RIDGE POSITIONED DIRECTLY TO THE NORTHWEST
OVER CENTRAL JAPAN

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 64 KTS AT 281420Z
   CIMSS ADT: 39 KTS AT 281930Z
   CIMSS AIDT: 54 KTS AT 281930Z
   CIMSS D-MINT: 42 KTS AT 281523Z
   CIMSS D-PRINT: 40 KTS AT 281930Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 12W IS FORECASTED TO SLOWLY TRACK TO THE
NORTH-NORTHWEST THROUGHOUT THE 120 FORECAST PERIOD DUE TO AN
ONGOING COMPETING STEERING ENVIRONMENT. IMMEDIATELY TO THE NORTH
OVER CENTRAL JAPAN, A SUBTROPICAL RIDGE IS EXPECTED TO SLOW ANY
SIGNIFICANT MOVEMENT NORTHWARD THROUGH TAU 120. DEPENDENT ON THE
STRENGTH OF THE AFOREMENTIONED RIDGE TO THE NORTH, THE SPEED OF
APPROACH AND DIRECTION OF TS KROSA TO THE NORTH COULD CHANGE
DRASTICALLY AS THE SYSTEM SIMULTANEOUSLY INTERACTS WITH A
DEEP-LAYER SUBTROPICAL RIDGE TO THE EAST. IF THE WELL-ENTRENCHED
RIDGE TO THE NORTH BUILDS OVER THE NEXT 72 HOURS, POTENTIAL MODEL
SOLUTIONS TRACK TS 12W NORTHWESTWARD TOWARD THE EASTERN COAST OF
HONSHU. IF THE SAME RIDGE WEAKENS, TS 12W MAY TRACK NORTHEASTWARD
ALONG THE NORTHWEST PERIPHERY OF THE SUBTROPICAL RIDGE TO THE EAST.
THEREFORE, TS KROSA IS EXPECTED TO SLOWLY PROGRESS NORTHWARD
THROUGH TAU 120. WITH REGARD TO INTENSITY, THE SLOW-MOVING NATURE OF
THE SYSTEM HAS CAUSED SIGNIFICANT UPWELLING, RESTRICTING INTENSITIES
TO 50-55 KTS BY THE END OF THE FORECAST PERIOD. COUPLED WITH DRY
AIR FROM THE WEST, TS 12W IS FORECASTED TO MAINTAIN 50 KTS THROUGH
THE INITIAL 72 HOURS OF THE FORECAST PERIOD AND SLOWLY INTENSIFY TO
55 KTS THEREAFTER AS THE SYSTEM RE-MOISTENS IN A LOW VWS
ENVIRONMENT.

MODEL DISCUSSION: TS 12W IS IN GOOD AGREEMENT THROUGH THE INITIAL
12 HOURS OF THE FORECAST PERIOD BUT BIFURCATES SIGNIFICANTLY
THEREAFTER. NEAR TAU 12, THE CROSS-TRACK SPREAD IS 46 NM, HOWEVER,
INCREASES TO 307 NM BY TAU 120. THEREFORE, THE JTWC TRACK FORECAST
HAS BEEN PLACED WITH LOW CONFIDENCE THROUGH TAU 120 DUE TO
DISAGREEMENT AMONGST JTWC CONSENSUS SOLUTIONS. THE INTENSITY
GUIDANCE HOWEVER WAS ASSESSED WITH MEDIUM CONFIDENCE AND ALIGNED
CLOSELY WITH THE JTWC INTENSITY CONSENSUS.  

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