WDPN33 PGTW 232100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (NEPARTAK) WARNING 
NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.7N 149.4E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 253 NM WEST OF MINAMI TORI SHIMA
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AND EARLY
MORNING VISUAL FRAMES DEPICT AN AREA OF VIGOROUS DEEP CONVECTION
JUST TO THE EAST OF AN EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC).
A 231839Z SSMIS SERIES VERIFIES THE EXISTENCE OF LOW LEVEL BANDING
AROUND THE CORE BUT AN ABSENCE OF CONVECTION CONSISTENT WITH THE
SIGNATURE OF A SUB-TROPICAL SYSTEM. THE INITIAL POSITION IS PLACED
WITH MEDIUM CONFIDENCE BASED ON THE EXPOSED LOW LEVEL CIRCULATION.
A DVORAK ESTIMATE OF T2.5 USING THE SUB-TROPICAL TECHNIQUE IS USED
FOR THE INITIAL INTENSITY ASSESSMENT. AN AMSU RADIAL HEIGHT AND
CROSS SECTION ANALYSIS PILES ONTO THE EVIDENCE THAT TROPICAL STORM
NEPARTAK IS A SUBPTROPICAL SYSTEM.

INITIAL WIND RADII BASIS: PERSISTENCE FROM A 231021 SCATTEROMETRY
PASS.  

CURRENT STEERING MECHANISM: A SHARP, HIGH-AMPLITUDE AND NARROW
SUBTROPICAL RIDGE TO THE EAST OF THE SYSTEM IS FORCING THE VORTEX
POLEWARD. 


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   CIMSS ADT: 30 KTS AT 231740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: LOW OCEAN HEAT CONTENT AND DRY AIR ENTRAINMENT
ASSOCIATED WITH A DEEP UPPER LEVEL TROUGH. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   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 11W IS A SUBTROPICAL SYSTEM. 
TROPICAL STORM 11W WILL NOT CHANGE INTO A TROPICAL SYSTEM. IT WILL 
NOT DEVELOP INTO A VIGOROUS STORM AND MAY NOT TOP 50 KNOTS ALONG ITS 
TRACK TOWARDS THE EAST COAST OF JAPAN, BUT IT WILL GENERATE SOME 
RAISED SURF FOR THE OLYMPIC SURFING EVENTS. ITS ORIGIN AT THE 
EASTERN EDGE OF A MONSOON GYRE PLACES IT WITHIN THE DIVERGENT REGION 
OF A DEEP SUBTROPICAL TROUGH WITH EXCELLENT EQUATORWARD OUTFLOW BUT 
HIGH VERTICAL WIND SHEAR. THE ASYMMETRIC WIND FIELD REVEALED BY THE 
EARLIER SCATTEROMETER PASS IS TYPICAL OF SUBTROPICAL CYCLONES. 


MODEL DISCUSSION: MODEL GUIDANCE OVER THE PAST TWO DAYS HAS BEEN
CONSISTENT IN INDICATING A TRACK TOWARDS THE TOHOKU REGION OF
JAPAN. BY THE TIME THE STORM REACHES THE COAST, HOWEVER, THERE IS A
WIDE SPREAD IN WHERE THE STORM MAY STRIKE, WITH OUR TWO
CHAMPIONS--ECMWF AND GFS--BEING THE OUTLIERS OF THE CONSENSUS
MEMBERS. ECMWF POINTS TO THE NORTHERN CHIBA PENINSULA, WHILE GFS
POINTS TOWARDS MISAWA. THE REST OF THE GUIDANCE IS PACKED BETWEEN
THE TWO, WITH THE MEAN POINTING AT SENDAI. THE KEY POINT IN THE
TRACK IS THE 30TH LATITUDE, WHERE THE STORM IS EXPECTED TO MAKE ITS
TURN TO THE NORTHWEST. AS IT DOES THAT, THE CERTAINTY OF WHERE THE
STORM WILL COME ASHORE WILL INCREASE SHARPLY.  UNTIL WE SEE THE
STORM ROUND THAT TURN, FORECAST TRACK UNCERTAINTY WILL REMAIN HIGH.
THE INTENSITY FORECAST IS MUCH EASIER: IN ADDITION TO THE STORM
BEING A SUB-TROPICAL SYSTEM, THE SYSTEM WILL ENCOUNTER HIGH
VERTICAL WIND SHEAR AND LOW OCEAN HEAT CONTENT THROUGH THE DURATION
OF ITS TRACK. THE INTENSITY FORECAST LIES ON THE HIGH SIDE OF THE
INTENSITY CONSENSUS MEAN. TROPICAL STORM NEPARTAK IS NOT EXPECTED
TO EVER REACH TYPHOON STRENGTH. 


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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