WDPN33 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (NEPARTAK) WARNING 
NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 36.4N 142.1E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 134 NM EAST-NORTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
11W (NEPARTAK) REMAINS ASSESSED AS A SUBTROPICAL STORM AT THIS
TIME. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
SHALLOW BANDING WRAPPING INTO A FULLY EXPOSED LOW LEVEL CIRCULATION
CENTER (LLCC). DISORGANIZED, MODERATE CONVECTIVE ACTIVITY IS
SCATTERED IN A NARROW BAND OF MOIST INFLOW ACROSS THE NORTHERN
HEMISPHERE OF THE SYSTEM, WHILE DRIER AIR AND MID-LEVEL CONVERGENCE
IS HINDERING SIGNIFICANT CONVECTIVE DEVELOPMENT IN THE SOUTHERN
HEMISPHERE OF THE SYSTEM. 11W IS VERTICALLY STACKED UNDER AN
UPPER-LEVEL LEVEL LOW AND CONTINUES TO EXHIBIT THE THERMAL
STRUCTURE OF A SUBTROPICAL SYSTEM, WITH AN UPPER-TROPOSPHERIC WARM
ANOMALY OVERLYING A LOW TO MID-LEVEL COLD ANOMALY. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED
LLCC, ANIMATED RADAR DATA AND A 271158Z ASCAT-B BULLSEYE PASS. THE
INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE, A IS SLIGHTLY
HIGHER THAN THE PGTW SUBTROPICAL DVORAK INTENSITY ESTIMATE OF T2.5,
BASED ON THE AFOREMENTIONED ASCAT PASS WHICH INDICATED A SWATH OF
30-34 KNOT WINDS CONFINED TO THE EASTERN HEMISPHERE OF THE SYSTEM.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: LOW TO MID-LEVEL SUBTROPICAL RIDGE
(STR) LOCATED TO THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T1.5 - 25 KTS
   CIMSS SATCON: 49 KTS AT 270323Z
   CIMSS ADT: 41 KTS AT 271140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 0-5 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: WEAK RADIAL
   OTHER FACTORS: AS THE SYSTEM LIES UNDER AN UPPER-LEVEL CYCLONE,
THERE IS NO TRADITIONAL OUTFLOW MECHANISM. ADDITIONALLY, WHILE
SHEAR IS LOW AND SSTS ARE HIGH, THE PRESENCE OF THE UPPER-LEVEL LOW
PRECLUDES ANY SIGNIFICANT TROPICAL DEVELOPMENT. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: WHILE THE OVERALL FORECAST PHILOSOPHY
HAS NOT CHANGED, THE CURRENT FORECAST HAS BEEN TRUNCATED TO 48
HOURS BASED ON THE LOWER CURRENT INTENSITY ASSESSMENT AND ADJUSTED
TIMELINE TO DISSIPATION. 

FORECAST DISCUSSION: WHILE CONTINUING TO TRACK STEADILY
NORTH-NORTHWESTWARD, 11W HAS SOMEWHAT UNEXPECTEDLY SLOWED OVER THE
PAST SIX HOURS, WITH CURRENT FORWARD MOTION ASSESSED AT SIX KNOTS.
THE FORECAST CALLS FOR THE SYSTEM TO PICK UP FORWARD SPEED OVER THE
NEXT 12 HOURS, AND MAKE LANDFALL NEAR SENDAI NEAR 280000Z. AFTER
MAKING LANDFALL, THE SYSTEM WILL TURN MORE NORTHWESTWARD AS THE
PRIMARY STEERING MECHANISM SWITCHES OVER TO A WEAK LOW TO MID-LEVEL
RIDGE EXTENDING FROM THE SEA OF OKHOTSK TO THE WESTERN PORTION OF
THE SEA OF JAPAN. AFTER CROSSING THE JAPANESE ALPS AND EMERGING
BACK OVER WATER BY TAU 24, THE SYSTEM WILL THEN TRACK WESTWARD INTO
THE CENTRAL SEA OF JAPAN. SLOW BUT STEADY WEAKENING IS FORECAST
OVER THE NEXT 12 HOURS, WITH LANDFALL INTENSITY EXPECTED TO BE 30
KTS. AFTER CROSSING THE RUGGED TERRAIN OF NORTHERN HONSHU, THE
SYSTEM WILL EMERGE BACK OVER WATER AT 25 KTS. BY TAU 36, THE
UPPER-LEVEL LOW, WHICH IS CURRENTLY PROVIDING SHELTER FROM THE
IMPACTS OF VWS, WILL MOVE EAST AND OPEN UP 11W TO THE IMPACT OF
VERY HIGH WIND SHEAR ASSOCIATED WITH A FINGER OF THE JET STREAM,
RESULTING IN THE FULL DISSIPATION OF THE SYSTEM NO LATER THAN TAU
48.   

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE HAS COME INTO BETTER
AGREEMENT WITH THE CURRENT RUN, WITH ALL CONSENSUS MEMBERS IN TIGHT
AGREEMENT THROUGH THE DURATION OF THE FORECAST, LENDING HIGH
CONFIDENCE TO THE JTWC FORECAST TRACK, WHICH LIES NEAR TO BUT
SLIGHTLY SLOWER THAN THE CONSENSUS MEAN. THE JTWC INTENSITY
FORECAST LIES SLIGHTLY BELOW THE INTENSITY CONSENSUS MEAN AND
SUPPORTS THE JTWC FORECAST. HOWEVER, THE INTENSITY FORECAST HAS
ONLY MEDIUM CONFIDENCE DUE TO THE UNCERTAINTIES ASSOCIATED WITH THE
INFLUENCE OF TERRAIN INTERACTION AND THE ULTIMATE STRENGTH OF THE
LLCC THAT EMERGES INTO THE SEA OF JAPAN. 


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