WDPN31 PGTW 292100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
025//
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 01 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
NEAR-STATIONARY CYCLONE WITH TIGHTLY COILED, WELL-ORGANIZED
STRUCTURE. HOWEVER, DEEP CONVECTION REMAINS SPORADIC WITH POOR
COVERAGE, LIKELY BECAUSE OF ONGOING OCEANIC UPWELLING BENEATH THE
STORM DUE TO ITS SLOW MOTION, AS ANALYZED BY THE COUPLED HAFS-A
MODEL. THE CYCLONE REMAINS EMBEDDED IN A DRY BROAD-SCALE
ENVIRONMENT, WITH DEEPLY DRY AIR OBSERVED AROUND THE ENTIRE
PERIPHERY OF THE CIRCULATION EXCEPT FOR THE NORTHEASTERN QUADRANT.
VERTICAL WIND SHEAR IS LOW, WITH WEAK RADIAL CIRRUS OUTFLOW
OBSERVED. THE INITIAL INTENSITY IS LOWERED TO 40 KT BASED ON A
BLEND OF OBJECTIVE SATELLITE-BASED INTENSITY ESTIMATES AND AGENCY
DVORAK INTENSITY ESTIMATES, SUPPORTED BY AN EARLIER 291404Z OSCAT-3
SCATTEROMETER PASS.

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
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 33 KTS AT 291730Z

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 TO THE NORTH, WEST, AND
SOUTH

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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) CONTINUES TO DRIFT
NORTHWARD AT A CRAWL. THIS IS A DEFINING FEATURE OF THE STORM AT
THIS TIME, AS OCEANIC UPWELLING OCCURRING DUE TO THE SLOW MOTION IS
ACTIVELY ERODING THE CYCLONE'S CONVECTIVE STRUCTURE, PREVENTING
INTENSIFICATION. PROGRESS TOWARDS THE NORTH AND THEN NORTHWEST IS
EXPECTED TO ACCELERATE OVER THE NEXT 72 HOURS, BRINGING KROSA OUT
OF ITS SELF-GENERATED COLD WAKE AND INTO WARMER WATERS OF 28 TO 29
DEGREES CELSIUS. WHILE KROSA WILL REMAIN NEARLY ENCIRCLED BY A
DEEPLY DRY AIR MASS DURING THIS TIME, LOW VERTICAL SHEAR SHOULD
ALLOW THE STORM TO TAKE ADVANTAGE OF THESE WARMER WATERS AND
REINTENSIFY SOMEWHAT THROUGH 72 HOURS. HOWEVER, INTENSIFICATION IS
CURRENTLY EXPECTED TO BE MODERATED BY THE DRY AIR AND BACKGROUND
OCEANIC HEAT CONTENT OF ONLY 15 TO 30 KJ PER SQUARE CENTIMETER.
REGARDING THE TRACK FORECAST, WHILE DYNAMICAL MODELS ARE IN
AGREEMENT ON A GRADUAL ACCELERATION TOWARDS THE NORTH AND
NORTHWEST, THERE IS SIGNIFICANT SPREAD IN THE EXACT TRACK. THIS IS
BECAUSE 12W IS CURRENTLY EMBEDDED IN A REVERSE-ORIENTED MONSOON
TROUGH WITH ILL-DEFINED STEERING BETWEEN A DEEP-LAYER RIDGE TO ITS
NORTH (OVER JAPAN) AND THE BELT OF SOUTHWESTERLY MONSOON FLOW TO
ITS SOUTH. MODEL SPREAD IS OVER 300 NM AT 72 HOURS AS A RESULT,
WHICH CREATES UNCERTAINTY REGARDING HOW CLOSE TO HONSHU 12W WILL
TRACK. AS THE STORM MOVES NORTHWARD, INCREASING PROXIMITY TO THE
JAPANESE RIDGE IS EXPECTED TO CAUSE A BEND NORTHWESTWARD, FOLLOWED
BY A TURN NORTHEASTWARD AS THE RIDGE DECAYS AND RELEASES THE STORM
INTO THE MID-LATITUDE WESTERLIES. THE JTWC TRACK FORECAST IS
SIMILAR TO BUT SLIGHTLY WEST OF THE PREVIOUS ONE, TRACKING WITHIN
45 NM OF YOKOSUKA. ENSEMBLE GUIDANCE MAKES CLEAR THAT A TRACK
DIRECTLY STRIKING SOUTHEASTERN HONSHU IS WITHIN THE RANGE OF
POSSIBILITIES, AS IS A TRACK WELL OFFSHORE. OVERALL CONFIDENCE IN
THE TRACK FORECAST IS LOWER THAN AVERAGE DUE TO THE COMPLEX
STEERING ENVIRONMENT AND HIGH MODEL SPREAD. AFTER THE ULTIMATE TURN
NORTHEASTWARD, WEAKENING IS ANTICIPATED ONCE 12W MOVES NORTH OF THE
KUROSHIO CURRENT AND BEGINS EXTRATROPICAL TRANSITION.

MODEL DISCUSSION: THE JTWC TRACK FORECAST IS CLOSE TO THE
MULTI-MODEL CONSENSUS THROUGH 48 HOURS, THEN SLIGHTLY WEST OF IT
THEREAFTER. THE JTWC INTENSITY FORECAST IS SLIGHTLY ABOVE THE
MULTI-MODEL CONSENSUS, LEANING TOWARDS COAMPS-TC DUE TO THE
ANTICIPATED IMPROVEMENT IN OCEANIC CONDITIONS THROUGH 72 HOURS.

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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