WDPN31 PGTW 121500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (MEARI) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.9N 136.7E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 253 NM SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THAT THE
LOW LEVEL CIRCULATION CENTER (LLCC) OF TS 09W REMAINS FIRMLY AND
STUBBORNLY FULLY EXPOSED, WITH CONVECTION SIMPLY UNABLE TO
CONSOLIDATE NEAR THE CORE DUE TO THE PERSISTENT NORTH-NORTHWESTERLY
FLOW. WHILE SHEAR VALUES ARE IN THE MODERATE (15-20 KNOTS), THE
ORIENTATION OF THE UPPER-LEVEL FLOW (TURNING ANTI-CYCLONICALLY OVER
THE SYSTEM) IS BRINGING UPPER-LEVEL MASS CONVERGENCE AND DOWNWARD
VERTICAL MOTION OVER THE SYSTEM, INHIBITING CONVECTIVE DEVELOPMENT
AND INTENSIFICATION. OTHERWISE THE ENVIRONMENT REMAINS FAVORABLE,
WITH WARM (28-29C) SSTS AND STRONG EQUATORWARD OUTFLOW. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC
IN THE SHORTWAVE INFRARED IMAGERY. THE INITIAL INTENSITY REMAINS
SET AT 35 KNOTS, HEDGED SLIGHTLY HIGHER THAN THE AGENCY DVORAK
CURRENT INTENSITY ESTIMATES, TOWARDS THE ADT, AIDT AND SATCON
ESTIMATES RANGING FROM 34-38 KNOTS. LATE RECEIPT OF A 121214Z
PARTIAL ASCAT-B PASS CONFIRMS 35 KNOT WINDS ON THE EASTERN
PERIPHERY OF THE SYSTEM, LENDING HIGHER CONFIDENCE TO THE INTENSITY
ASSESSMENT. THE SYSTEM CONTINUES TRACK NORTHWARD ALONG THE WESTERN
PERIPHERY OF A DEEP SUBTROPICAL RIDGE (STR) TO THE EAST.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 38 KTS AT 121051Z
   CIMSS ADT: 34 KTS AT 121140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: UPPER-LEVEL CONVERGENCE AND DOWNWARD VERTICAL
MOTION. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 09W HAS TRACKED JUST A SHADE RIGHT OF DUE
NORTH OVER THE PAST SIX HOURS, ALONG THE WESTERN SIDE OF THE
STEERING RIDGE CENTERED TO THE EAST. ALL EYES ARE WAITING WITH
BAITED BREATH FOR THE ANTICIPATED TURN TO THE NORTHEAST, WHICH ALL
AVAILABLE MODEL GUIDANCE SUGGESTS SHOULD BE IMMINENT. ONCE THE
RIDGE STARTS TO SLIDE SOUTHWARD, TS 09W WILL TURN SHARPLY
NORTHEASTWARD, SKIRT THE SOUTHERN COAST OF HONSHU, AND MAKE
LANDFALL ALONG THE SOUTHWESTERN IZU PENINSULA AROUND TAU 18. THE
SYSTEM IS THEN EXPECTED TO PASS RAPIDLY THROUGH THE TOKYO METRO
AREA AND THEN EMERGE BACK OVER WATER BY AROUND TAU 24, ACCELERATING
ON A NORTHEASTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST. IN
TERMS OF INTENSITY, THE CHANGE IN THE UPPER-LEVEL FLOW PATTERN
WHICH HAS INDUCED THE STRONGLY NEGATIVE CONVERGENT FLOW REGIME
MEANS THAT THE SYSTEM WILL NOT HAVE SUFFICIENT TIME REMAINING OVER
OPEN WATERS TO INTENSIFY ALL THAT MUCH. THE MODEL GUIDANCE HOWEVER
IS STILL HOLDING OUT HOPE THAT AN IMPROVEMENT IN THE UPPER-LEVEL
OUTFLOW PATTERN IS FORTHCOMING IN THE NEXT 12 TO 24 HOURS, AND THUS
THE SYSTEM MAY YET HAVE A CHANCE AT MARGINAL INTENSIFICATION PRIOR
TO LANDFALL. THE PEAK INTENSITY IS NOW FORECAST TO REACH 45 KNOTS
BY TAU 24. AFTER MOVING BACK OVER THE SIGNIFICANTLY COOLER WATERS
NORTHEAST OF HONSHU, THE SYSTEM WILL BEGIN TO INTERACT WITH A
ROBUST UPPER-LEVEL TROUGH AND WILL EXPERIENCE ENOUGH BAROCLINIC
FORCING TO MAINTAIN A 45 KNOT INTENSITY THROUGH TAU 36 WHILE
BEGINNING EXTRATROPICAL TRANSITION (ETT). THE SYSTEM IS FORECAST TO
COMPLETE ETT AND BECOME A COLD-CORE, GALE-FORCE EXTRATROPICAL LOW
EAST OF HOKKAIDO BY TAU 48. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT, WITH
ALL MEMBERS OF THE CONSENSUS CONSTRAINED WITHIN A 50NM ENVELOPE
THROUGH TAU 24, EXPANDING SLIGHTLY TO 70NM BY TAU 36. THIS TIGHT
ENVELOPE WOULD SUGGEST HIGH CONFIDENCE IN THE TRACK FORECAST, BUT
THE FACT THAT THE CURRENT TRACK IS DUE NORTH WITH NO SIGN YET OF A
TURN TO THE NORTH IS INDUCING SOME DECREASED CONFIDENCE IN THE
TRACK. THE LONGER THE TURN NORTHEAST IS DELAYED, THE FURTHER WEST
THE TRACK WILL SLIDE. CONFIDENCE IS THUS MEDIUM EVEN WITH THE VERY
LOW MODEL SPREAD. INTENSITY GUIDANCE HAS COME DOWN SIGNIFICANTLY
WITH THIS RUN, WITH THE BULK OF THE GUIDANCE NOW LYING BETWEEN 35
AND 45 KNOTS, WITH ONLY THE CTCX INDICATING A HIGHER, ALBEIT
UNREALISTIC AT THIS POINT, 60 KNOT PEAK. THUS THE FORECAST HAS COME
DOWN TO 45 KNOTS, WHICH IS ON THE UPPER END OF THE ENVELOPE. 

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