WDPN31 PGTW 060900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YUN-YEUNG)    
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.5N 134.3E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 596 NM SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED, WELL-DEFINED LOW-LEVEL CIRCULATION CENTER (LLCC)
POSITIONED UNDER THE NORTHERN EDGE OF AN AREA OF EXPANDING DEEP
CONVECTION. A 060426Z ATMS 88.2 GHZ MICROWAVE IMAGE INDICATES THE
DEEP CONVECTIVE AREA IS NOT WELL-ORGANIZED AND IS LINEAR, SHEARED
TOWARD THE SOUTHWEST. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE MSI. THE INITIAL INTENSITY OF 35 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE CIMSS ADT, AIDT, DPRINT, 
AND SATCON ESTIMATES. THE REMNANTS OF 11W (KIROGI), WHICH ARE 
CURRENTLY CENTERED ABOUT 322 NM NORTH OF 12W'S INITIAL POSITION, ARE 
UNDERGOING BINARY INTERACTION WITH 12W. MSI INDICATES THE REMNANTS OF 
11W ARE STILL INTACT BUT ARE BEGINNING TO WEAKEN SIGNIFICANTLY AS THEY 
INTERACT WITH THE OUTER PERIPHERY OF 12W AND ACCELERATE SOUTHEASTWARD 
TO SOUTHWARD.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: PRIMARY: LOW- TO MID-LEVEL SUBTROPICAL
RIDGE (STR) POSITIONED TO THE EAST. SECONDARY (THROUGH TAU 24): BINARY 
INTERACTION WITH THE REMNANTS OF 11W (KIROGI). 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 36 KTS AT 060447Z
   CIMSS ADT: 34 KTS AT 060530Z
   CIMSS AIDT: 36 KTS AT 060530Z
   CIMSS DPRINT: 36 KTS AT 060700Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 5-10 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM (TS) 12W IS FORECAST TO TRACK
NORTH-NORTHEASTWARD ALONG THE WESTERN PERIPHERY OF THE STR THROUGH
TAU 24. TS 12W WILL QUICKLY ABSORB THE WEAKENING REMNANTS OF 11W
(KIROGI) WITHIN THE NORTHERN AND NORTHWESTERN QUADRANTS. THE BINARY 
INTERACTION OR FUJIWARA INTERACTION WILL INTRODUCE SOME UNCERTAINTY IN 
THE EXACT TRACK OF TS 12W WITH A SHORT DURATION NORTHWARD TRACK 
POSSIBLE BEFORE 12W RESUMES A STEADY NORTH-NORTHEASTWARD TRACK CLOSE 
TO THE KANTO PLAIN. POLEWARD OUTFLOW IS EXPECTED TO IMPROVE IN 
RESPONSE TO A MIDLATITUDE SHORTWAVE TROUGH CURRENTLY DIGGING OVER 
SOUTH KOREA AND WESTERN JAPAN. IN FACT, ANIMATED WATER VAPOR IMAGERY 
INDICATES POLEWARD OUTFLOW IS BEGINNING TO EXPAND WITH DEEP CONVECTION 
NOW BUILDING OVER THE LLCC. THE IMPROVED ENVIRONMENTAL CONDITIONS WILL 
SUPPORT A SHORT (24 TO 36 HOURS) PERIOD OF INTENSIFICATION WITH A PEAK 
OF 45-50 KNOTS BY TAU 36. AFTER TAU 36, VERTICAL WIND SHEAR IS 
FORECAST TO INCREASE TO 30-40 KNOTS WITH INCREASING DRY AIR 
ENTRAINMENT LEADING TO A STEADY WEAKENING TREND AS THE SYSTEM 
APPROACHES AND PASSES THE KANTO PLAIN. THE MIDLATITUDE SHORTWAVE 
TROUGH IS EXPECTED TO QUICKLY PROPAGATE NORTHEASTWARD WITH THE STR 
REBUILDING, WHICH WILL TURN THE SYSTEM EAST-NORTHEASTWARD AFTER TAU 72 
WITH DISSIPATION ANTICIPATED BY TAU 96. DUE TO THE LACK OF A RECURVE 
MECHANISM AND BAROCLINIC ZONE, A TYPICAL RECURVE SCENARIO WITH EXTRA-
TROPICAL TRANSITION IS UNLIKELY. 

MODEL DISCUSSION: DETERMINISTIC AND PROBABILISTIC GUIDANCE SUPPORTS
THIS SCENARIO WITH A DISTINCT SLOW DOWN AND WEAKENING TREND
REFLECTED IN THE 060000Z GFS AND ECMWF ENSEMBLES. ADDITIONALLY, THERE 
ARE NO RECURVING SOLUTIONS, REINFORCING THE LACK OF A RECURVE 
MECHANISM. OVERALL, THERE IS MEDIUM CONFIDENCE IN THE JTWC FORECAST 
TRACK WITH MODEL GUIDANCE SHOWING SOME POTENTIAL FOR THE SYSTEM TO 
TRACK CLOSER TO THE KANTO PLAIN REGION. THE 060000Z COAMPS-TC ENSEMBLE 
SUPPORTS THE JTWC INTENSITY FORECAST OVER THE NEXT 36 HOURS WITH 
MODERATE INTENSIFICATION PROBABILITIES INCREASING TO 70 TO 80 PERCENT.

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