WDPN31 PGTW 290900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.5N 142.9E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 439 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A COMPACT
INNER-CORE, WTIH WELL-DEFINED LOW-LEVEL CLOUD LINES WRAPPING INTO A
SMALL LOW LEVEL CIRCULATION CENTER (LLCC). THE MSI ALSO DEPICTS
RAPID DEVELOPMENT OF VORTICAL HOT TOWERS IN CLOSE PROXIMITY TO THE
LLCC, ALONG THE SOUTHWESTERN SIDE OF THE VORTEX, AND BEGINNING
TO WRAP UPSHEAR TO THE EASTERN SIDE. ANIMATED WATER VAPOR IMAGERY
INDICATES THE SYSTEM IS COCOONED WITHIN A LARGE MASS OF DRY AIR,
HOWEVER THE INNER STRUCTURE OF THE SYSTEM, ROUGHLY INSIDE 200NM
FROM THE CENTER, IS SUFFICIENTLY MOIST TO SUPPORT ACTIVE
CONVECTION. THIS IS CONFIRMED BY THE CHICHIJIMA 290000Z SOUNDING
(APPROXIMATELY 100NM SOUTHWEST OF THE CENTER) WHICH SHOWED A
COMPLETELY SATURATED ATMOSPHERE UP TO ABOUT 400MB. CIMSS
ATMOSPHERIC MOTION VECTORS (AMVS), JTWC UPPER-LEVEL STREAMLINE
ANALYSIS AND GLOBAL MODEL FIELDS SUGGEST AN UPPER-LEVEL CYCLONE
OVERLAYS THE SYSTEM, THOUGH THE 200MB WINDS DO SHOW SOME
ANTICYCLONIC TURNING TO THE NORTH OF THE CENTER, PROVIDING SOME
WEAK POLEWARD OUTFLOW. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE OBVIOUS CENTER IN THE MSI. THE INITIAL
INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, HEDGED TOWARDS THE
HIGHER END OF THE AGENCY DVORAK FIXES AND THE SATCON. ENVIRONMENTAL
CONDITIONS ARE MARGINALLY FAVORABLE, WITH LOW SHEAR OFFSET BY WEAK
POLEWARD OUTFLOW AND OCEANIC UPWELLING, LOCALLY REDUCING SSTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: WEAK AND COMPETING STEERING PATTERN,
WITH A SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST AND A BUILDING STR
CENTERED ON THE NORTHERN COAST OF CENTRAL JAPAN. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 55 KTS AT 290401Z
   CIMSS ADT: 34 KTS AT 290540Z
   CIMSS AIDT: 38 KTS AT 290540Z
   CIMSS D-MINT: 42 KTS AT 290335Z
   CIMSS D-PRINT: 43 KTS AT 290700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY AIR SURROUNDING THE SYSTEM AT A DISTANCE OF
ABOUT 200NM. AN UPPER-LEVEL LOW OVER TOP OF THE SYSTEM. UPWELLING
FOR COOLER OCEAN WATERS. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THIS IS A SIGNIFICANT CHANGE IN THE
FORECAST PHILOSOPHY, EXTENDING THE FORECAST TRACK MUCH FURTHER
TOWARDS THE NORTHWEST, AND MUCH CLOSER TO JAPAN, THAN THE PREVIOUS
FORECAST. 

FORECAST DISCUSSION: TROPICAL STORM (TS) 12W IS FORECAST TO REMAIN
QUASI-STATIONARY OVER THE NEXT 12 TO 24 HOURS, GENERALLY MEANDERING
NORTHWARD, TRAPPED WITHIN A WEAK AND COMPETING STEERING PATTERN
BETWEEN STRONG RIDGING BOTH SOUTHEAST AND NORTHWEST OF THE SYSTEM.
OVER THE SAME TIME PERIOD, THE RIDGE TO THE SOUTHEAST WILL ELONGATE
AND WEAKEN, WHILE THE STR OVER JAPAN BUILDS AND EXTENDS TO THE
NORTHEAST, ALLOWING IT TO TAKE OVER AS THE DOMINATE STEERING
MECHANISM. AFTER TAU 36, THE CHANGE IN THE RIDGING PATTERN WILL BE
COMPLETE, WITH A BROAD REGION OF RIDGING IN PLACE TO THE NORTH OF
TS 12W, ROUGHLY EXTENDING FROM SOUTHERN HONSHU NORTHEASTWARD ALONG
THE JAPANESE MAIN ISLANDS, THEN EXTENDING OUT INTO THE NORTHWESTERN
PACIFIC. AS THIS RIDGE CONTINUES TO BUILD, TS 12W WILL TURN ONTO A
MORE NORTHWESTWARD TRACK, GENERALLY TOWARDS HONSHU. TRACK SPEEDS
BEGIN TO PICK UP AFTER TAU 48, AS THE SYSTEM COMES UNDER THE
INFLUENCE OF THE RIDGING TO THE NORTH. HOWEVER, BY TAU 96, A SUDDEN
AND DRAMATIC SHIFT IN THE TRACK IS ANTICIPATED, AS THE STR TO THE
SOUTHEAST RAPIDLY BUILDS AND UPPER-LEVEL TROUGHING DEEPENS OVER
JAPAN. THE COMBINATION OF STEERING INFLUENCES WILL TURN TS 12W
SHARPLY NORTHEASTWARD AS IT APPROACHES EASTERN HONSHU AROUND TAU
96. THE SYSTEM WILL THEN ACCELERATE RAPIDLY NORTHEASTWARD ALONG THE
TIGHT STEERING GRADIENT ALONG THE NORTHWESTERN SIDE OF THE STRONG
STR EAST OF IWO TO. IN TERMS OF INTENSITY, THE LACK OF STRONG
OUTFLOW ALOFT, AND THE CONTINUING UPWELLING OF COOLER OCEAN WATERS,
MEANS THAT TS 12W WILL STRUGGLE TO INTENSIFY OR EVEN MAINTAIN
INTENSITY FOR THE NEXT 12 TO 18 HOURS. AN ANTICIPATED SLOW DRIFT
NORTHWARD, COUPLED WITH A SLIGHTLY IMPROVED UPPER-LEVEL OUTFLOW
PATTERN, SHOULD ALLOW FOR SOME SLOW INTENSIFICATION AFTER TAU 24.
HOWEVER, OFFSETTING FACTORS WILL ONCE AGAIN HINDER DEVELOPMENT
THROUGH TAU 48. AFTER TAU 72, THE SYSTEM MOVES ACROSS THE WARMEST
WATERS OF KUROSHIO CURRENT, AND SIMULTANEOUSLY A TUTT-CELL DEVELOPS
TO ITS SOUTHWEST, OFFERING A BURST OF IMPROVED OUTFLOW, ALLOWING
THE SYSTEM TO INTENSIFY TO TYPHOON STRENGTH AS IT APPROACHES JAPAN.
THE SYSTEM WILL THEN BEGIN TO WEAKEN UNDER INCREASING SHEAR AND
DECREASING SSTS AS IT MOVES NORTHEASTWARD BEYOND TAU 96. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE HAS COME INTO BETTER
OVERALL AGREEMENT, WITH THE ENTIRE GUIDANCE ENVELOPE SHIFTING OVER
TOWARDS A NORTHWESTWARD TRACK. HOWEVER, SIGNIFICANT UNCERTAINTY
REMAINS, BOTH IN THE TIMING OF THE BREAKOUT FROM THE
QUASI-STATIONARY BUBBLE, AS WELL AS THE AMOUNT OF WESTERLY
COMPONENT IN THE TRACK. THE GFS IS A SIGNIFICANT WESTERLY OUTLIER,
TAKING THE SYSTEM FAR OUT TO THE WEST BEFORE SHARPLY TURNING IT
BACK NORTHEASTWARD AT TAU 96. THE JGSM MEANWHILE TRACKS THE SYSTEM
NORTHWARD THROUGH MOST OF THE FORECAST PERIOD BEFORE IT TOO SHIFTS
NORTHEASTWARD AFTER TAU 96. THE REMAINDER OF THE MODELS LIE
GENERALLY IN THE MIDDLE, WITH THE CONSENSUS MEAN, ECMWF, GEFS,
ECENS AND A COUPLE OF AI MODELS ALL TIGHTLY PACKED ABOUT THE MEAN.
CROSS-TRACK SPREAD EXCEEDS 300NM AT TAU 72, BUT THEN TIGHTENS UP
SLIGHTLY AFTER MAKING THE TURN NORTHEASTWARD, THOUGH ALONG-TRACK
SPREAD THEN INCREASES SHARPLY. THE JTWC FORECAST IS POSITIONED
CLOSE TO THE ECMWF AND ECENS SOLUTION THROUGH TAU 72, AND THE
CONSENSUS MEAN THROUGH TAU 120. CONFIDENCE IS LOW THROUGHOUT THE
FORECAST DUE TO LARGE UNCERTAINTY IN THE ENSEMBLE GUIDANCE AS WELL
AS THE DETERMINISTIC GUIDANCE. INTENSITY GUIDANCE IS IN GOOD
AGREEMENT OVERALL, WITH MINOR DEVIATIONS BOTH ABOVE AND BELOW THE
MEAN, BUT NO SIGNIFICANT OUTLIERS. THE JTWC FORECAST IS POSITIONED
CLOSE TO THE HAFS-A SOLUTION WITH MEDIUM CONFIDENCE. 

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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