WDPN31 PGTW 310900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (KROSA) WARNING NR 
031//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.1N 142.6E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 181 NM NORTH OF CHICHI JIMA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS RAGGED DEEP
CONVECTIVE BANDING WRAPPING INTO AN OBSCURED LOW-LEVEL CIRCULATION
CENTER (LLCC). A DISTINCTLY DRY ENVIRONMENT SURROUNDS THE SYSTEM ON
WATER VAPOR IMAGERY AND INHIBITS FURTHER DEVELOPMENT. THE 
INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE
AFOREMENTIONED DISORGANIZED STRUCTURE OF TROPICAL STORM (TS) 12W.
THE LLCC IS UNIDENTIFIABLE DUE TO THE MINIMAL POLAR ORBITING
SATELLITE DATA. THE INITIAL INTENSITY OF 45 KTS IS ASSESSED WITH
LOW CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE FIXES LISTED
BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: A COMPETING STEERING ENVIRONMENT
BETWEEN A WEAKENING SUBTROPICAL RIDGE OVER JAPAN AND AN ELONGATED
RIDGE TO THE SOUTHEAST ENHANCING MONSOONAL FLOW.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T3.0 - 45 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 52 KTS AT 310324Z
   CIMSS ADT: 33 KTS AT 310530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: LOW
   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 12W WILL REMAIN IN A WEAK STEERING
ENVIRONMENT BETWEEN THE SUBTROPICAL RIDGE (STR) TO THE NORTHWEST
AND THE NEAR EQUATORIAL RIDGE (NER) TO THE SOUTHEAST. THE STR WILL
WEAKEN DUE TO A SHORTWAVE TROUGH APPROACHING FROM THE WEST, CAUSING
A WEAK NORTHWARD TRACK WITH IRREGULAR MOTION ANTICIPATED. THE
TROUGH WILL BREAK DOWN THE STR BY TAU 36, RESULTING IN A TRACK
SHIFT TO THE EAST-NORTHEAST ON THE NORTHERN PERIPHERY OF THE NER
THROUGH THE REMAINDER OF THE FORECAST PERIOD. AFTER TAU 72, THE
SYSTEM WILL BEGIN EXTRATROPICAL TRANSITION AS THE SYSTEM INTERACTS
WITH AN UPPER-LEVEL TROUGH AND BECOME FRONTAL. IN THE NEAR-TERM
FORECAST, THE SYSTEM WILL WEAKLY INTENSIFY WHILE PASSING SLOWLY
OVER WATER WITH LOW OCEAN HEAT CONTENT, LEAVING BEHIND A COLD WAKE.
THE UPPER-LEVEL ENVIRONMENT WILL BE MARGINAL WITH A TROUGH TO THE
NORTHWEST ENHANCING POLEWARD OUTFLOW. DRY AIR WILL CONTINUE TO
ENCIRCLE TS 12W AND INTRUDE INTO THE CORE OF THE CIRCULATION. AFTER
REACHING A PEAK INTENSITY AT TAU 48 OF 60KTS WHILE TRACKING OVER
THE WARMER KUROSHIO CURRENT, TS 12W WILL WEAKEN AFTER CURVING
EAST-NORTHEASTWARD INTO COOLER WATER, HIGHER VERTICAL WIND SHEAR,
AND A BAROCLINIC ZONE.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT TS 12W WILL REMAIN IN A WEAK STEERING ENVIRONMENT. BINARY
INTERACTION WITH THE CYCLONE TO THE SOUTHWEST SEEMS TO INFLUENCE
THE TRACK LESS THAN REPRESENTED IN PREVIOUS MODEL RUNS. HOWEVER,
THE TRACK GUIDANCE HAS BEEN VARIABLE RUN-TO-RUN, AND THE TRACK
CONFIDENCE IS LOW. ENSEMBLE GUIDANCE OF COAMPS-TC, GEFS, AND ECENS
IS SPREAD BROADLY IN THE NEAR-TERM, BUT FEW MEMBERS MAKE LANDFALL
ON HONSHU. THE JTWC INTENSITY GUIDANCE IS CONSISTENT, FORECASTING A
PEAK INTENSITY OF 55-65KTS BETWEEN TAU 24-36. HOWEVER, THE
INTENSITY GUIDANCE IS HIGHLY DEPENDENT ON THE TRACK SPEED, AND
DEVIATIONS TO THE WEST MAY CAUSE THE SYSTEM TO PASS INTO COOLER 
WATERS ASSOCIATED WITH A COLD-CORE EDDY, WHILE DEVIATIONS TO THE EAST 
MAY BRING THE SYSTEM INTO SLIGHTLY WARMER WATERS IN THE KUROSHIO.

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