WDPN31 PGTW 300300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.7N 142.8E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 426 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 00 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A
NEAR-STATIONARY CYCLONE WITH A TIGHTLY COILED LLCC. DEEP CONVECTIVE
BANDING HAS SLIGHTLY IMPROVED IN COVERAGE OVER THE PAST FEW HOURS,
BUT REMAINS FRAGMENTED DUE TO ONGOING OCEANIC UPWELLING BENEATH THE
SLOW-MOVING CYCLONE AS DIAGNOSED BY THE COUPLED HAFS-A MODEL. A
DEEP-LAYER DRY AIR MASS CONTINUES TO SURROUND THE CYCLONE IN WATER
VAPOR SATELLITE IMAGERY. WEAK UPPER-LEVEL RADIAL OUTFLOW IS
OBSERVED IN ALL QUADRANTS. THE INITIAL INTENSITY IS HELD AT 40 KT
BASED ON A BLEND OF OBJECTIVE SATELLITE-BASED INTENSITY ESTIMATES
AND AGENCY DVORAK INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: COMPETING STEERING INFLUENCES FROM A
DEEP-LAYER RIDGE OVER JAPAN AND THE SOUTHWESTERLY MONSOON FLOW BELT
TO THE SOUTH

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T3.5 - 55 KTS
   CIMSS SATCON: 40 KTS AT 292141Z
   CIMSS ADT: 33 KTS AT 292030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 0-5 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK RADIAL
   OTHER FACTORS: DEEP-LAYER DRY AIR MASS ON PERIPHERY OF
CIRCULATION

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM 12W (KROSA) REMAINS NEARLY
STATIONARY IN A COMPLEX STEERING ENVIRONMENT, STUCK BETWEEN A
DEEP-LAYER RIDGE TO THE NORTH (OVER JAPAN) AND A BELT OF MONSOONAL
SOUTHWESTERLY FLOW TO THE SOUTH. THIS IS SIGNIFICANTLY RESTRAINING
THE STORM'S INTENSITY AT THE MOMENT DUE TO ONGOING OCEANIC
UPWELLING BENEATH THE CIRCULATION. KROSA IS EXPECTED BY ALL
DYNAMICAL MODELS TO BEGIN MAKING GRADUAL PROGRESS NORTHWARD OVER
THE NEXT 24 HOURS, EVENTUALLY ACCELERATING ON A NORTHWESTWARD BEND
AS THE JAPANESE RIDGE GAINS MORE STEERING INFLUENCE OVER 12W. BY 72
HOURS, MODELS DISAGREE SIGNIFICANTLY ON HOW FAR WEST THIS BEND WILL
TAKE THE STORM. SOME RUNS TAKE 12W AS FAR WEST AS A POINT OFFSHORE
OF WAKAYAMA, JAPAN BEFORE CHECKMARKING NORTHEASTWARD, WHILE OTHERS 
STAY EAST OF TOKYO'S LONGITUDE. MOST MODELS DO AGREE THAT THE RIDGE 
OVER JAPAN IS EXPECTED TO WEAKEN AND ERODE AFTER 72 HOURS, RELEASING 
THE STORM INTO THE MID-LATITUDE WESTERLIES ON A NORTHEASTWARD HEADING. 
WHERE THIS TURN OCCURS WILL GOVERN WHETHER 12W MAKES LANDFALL IN 
HONSHU. ENSEMBLE GUIDANCE CONTINUES TO INDICATE THAT LANDFALL REMAINS 
WITHIN THE RANGE OF POSSIBLE OUTCOMES, BUT A TRACK THAT STAYS OFFSHORE 
IS MORE LIKELY AT THIS TIME. THE JTWC TRACK FORECAST IS SIMILAR TO THE 
PREVIOUS ONE, SHIFTED SLIGHTLY FARTHER WEST THROUGH 72 HOURS. OVERALL
CONFIDENCE IN THE TRACK FORECAST IS LOWER THAN AVERAGE DUE TO THE 
COMPLEX STEERING ENVIRONMENT AND ELEVATED MODEL SPREAD. REGARDING
THE INTENSITY FORECAST, AS 12W ACCELERATES NORTHWESTWARD, IT WILL
ESCAPE ITS SELF-GENERATED COLD WAKE AND LIKELY INTENSIFY SOMEWHAT
OVER WARMER WATERS OF 28 TO 29 DEGREES CELSIUS NEAR THE KUROSHIO
CURRENT. HOWEVER, A COLD EDDY SOUTH OF YOKOSUKA AND GENERALLY LOW
OCEAN HEAT CONTENT VALUES OF 15 TO 30 KJ PER SQUARE CENTIMETER
ALONG THE FORECAST TRACK IS LIKELY TO MODERATE THE INTENSIFICATION
THAT OCCURS. THE JTWC INTENSITY FORECAST PEAKS AT 60 KT AT 72
HOURS, THOUGH SOME ADDITIONAL STRENGTHENING COULD OCCUR DURING THE
TIME BETWEEN THE 72-HOUR AND 96-HOUR FORECAST POINTS.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS GENERALLY CLOSE TO THE
MULTI-MODEL CONSENSUS, LEANING TOWARDS A BLEND OF ECMWF, ECMWF
ENSEMBLE MEAN, GFS, GFS ENSEMBLE MEAN, AND AVAILABLE AI-BASED MODEL
GUIDANCE. THE JTWC INTENSITY FORECAST IS CLOSE TO THE MULTI-MODEL
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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