WDPN32 PGTW 131500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUBTROPICAL DEPRESSION 07W (SEVEN)   
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.1N 127.8E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 154 NM SOUTHWEST OF SASEBO, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
THIS SYSTEM IS CLASSIFIED AS A SUBTROPICAL CYCLONE, WITH STRUCTURAL
FEATURES CHARACTERISTIC OF BOTH TROPICAL AND MID-LATITUDE CYCLONES.
THIS WARNING IS PROVIDED AS A SPECIAL ISSUANCE TO FACILITATE
RESOURCE PROTECTION. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS A FULLY EXPOSED, BROAD LOW-LEVEL CIRCULATION, WITH
FRAGMENTED, SHALLOW BANDING WRAPPING INTO A DEFINED CENTER. EIR
IMAGERY SHOWS FLARING ISOLATED CONVECTION SHEARED TO THE NORTHEAST.
ENVIRONMENTAL CONDITIONS HAVE GRADUALLY DEGRADED OVER THE PAST SIX
HOURS, WITH INCREASING VERTICAL WIND SHEAR OF 20-25 KNOTS. A
131212Z ASCAT-C IMAGE PROVIDES SOLID EVIDENCE OF THE SIGNIFICANT
WEAKENING OF THIS SYSTEM, WITH 15-20 KNOT VECTORS OVER THE WESTERN
AND SOUTHERN QUADRANTS, WHICH SUGGESTS A BORDERLINE INTENSITY OF
ABOUT 25 KNOTS. ADDITIONALLY, THE CIRCULATION HAS WEAKENED AND
STARTED TO OPEN UP OVER THE NORTHEASTERN QUADRANT. OVERALL, THERE
IS HIGH CONFIDENCE IN THE INITIAL POSITION AND INITIAL INTENSITY.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: LOW-LEVEL STEERING RIDGE POSITIONED TO
THE SOUTH, WITH THE STR POSITIONED NORTHEAST OF THE SYSTEM OVER THE 
SEA OF JAPAN. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS ADT: 29 KTS AT 131130Z
   CIMSS AIDT: 36 KTS AT 131130Z
   CIMSS D-PRINT: 24 KTS AT 131330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: DUE TO THE RAPIDLY WEAKENING SYSTEM
AND EXPECTED TRACK OVER KYUSHU, THERE ARE MAJOR CHANGES TO BOTH THE 
JTWC TRACK AND INTENSITY FORECAST.

FORECAST DISCUSSION: SUBTROPICAL DEPRESSION (SD) 07W IS EMBEDDED
WITHIN A DEEP UPPER-LEVEL MAJOR SHORTWAVE TROUGH POSITIONED OVER
THE KOREAN PENINSULA AND EAST CHINA SEA. THIS IS FORECAST TO DRIVE
THE SYSTEM EASTWARD TO EAST-NORTHEASTWARD THROUGH TAU 12, WITH
LANDFALL OVER WESTERN KYUSHU EXPECTED WITHIN ABOUT NINE HOURS. THE
LATEST SATELLITE IMAGERY AT 131440Z CONTINUES TO SHOW A STEADY
EAST-NORTHEASTWARD TRAJECTORY. AFTER TAU 12, THE SYSTEM IS EXPECTED
TO TURN POLEWARD, TRACKING OVER KYUSHU AND WESTERN HONSHU, WITH
DISSIPATION BY TAU 24.

MODEL DISCUSSION: DETERMINISTIC GUIDANCE CONTINUES TO SHOW A LARGE 
SPREAD, WITH A BIFURCATION. GFS AND NAVGEM INDICATE AN EAST-
NORTHEASTWARD TRACK TOWARD SOUTHERN KYUSHU WHILE UEMI, AEMI AND EGRI 
SHOW A SHARPER POLWARD TURN INTO THE KOREAN STRAIT. ECMWF AND THE 
ECENS TRACKER NO LONGER ARE TRACKING A VIABLE VORTEX CENTER DUE TO THE 
WEAK NATURE OF THIS SYSTEM. THE 130600Z GEFS RUN CONTINUES TO SHOW A 
BIFURCATION, WITH THE BULK OF THE SOLUTIONS TRACKING THE SYSTEM OVER 
KYUSHU AND THE REMAINDER SHOWING A POLEWARD TRACK INTO THE SEA OF 
JAPAN THEN OVER THE KOREAN PENINSULA. AN ADDITIONAL FACTOR IS THE 
FORMATION OF A STRONG UPPER-LEVEL LOW OVER THE KOREAN PENINSULA WITHIN 
THE NEXT 24 HOURS, WITH MULTIPLE VORTICITY MAXIMUMS MERGING INTO ONE 
LARGE, DYNAMIC, COMPLEX UPPER-LEVEL LOW. THEREFORE, THERE IS POTENTIAL 
AND UPPER-LEVEL SUPPORT FOR THE FORMATION OF MULTIPLE SURFACE LOWS. 
THE 130600Z HAFS-A RUN SHOWS SD 07W APPROACHING WESTERN KYUSHU AND 
DISSIPATING, WITH ANOTHER SUBTROPICAL LOW FORMING NEAR 35N 129E THEN 
TRACKING THE SYSTEM POLEWARD INTO THE WESTERN SEA OF JAPAN. THE 
130600Z GFS RUN ALSO SHOWS DISSIPATION AND THE FORMATION OF ANOTHER 
LOW NEAR 36N 129E.             

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