Tropical Storm NEPARTAK Advisory sab, 24.07.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (NEPARTAK) WARNING
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
   INITIAL POSITION: 25.0N 149.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 799 NM SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT THE LOW
LEVEL CIRCULATION CENTER (LLCC) OF TROPICAL STORM NEPARTAK IS FULLY
EXPOSED AND BREAKING AWAY FROM THE BAND OF DEEP CONVECTION AT THE
BASE OF THE MONSOON GYRE. VIGOROUS WESTERLIES ALOFT ARE SHEARING
THE CLOUD BAND TO THE EAST OF THE VORTEX. THE SATELLITE IMAGERY,
AMSU RADIAL HEIGHT AND CROSS SECTION ANALYSIS, AND STRETCHED 850 MB
VORTICITY PATTERN ARE INDICATIVE OF A SUB-TROPICAL SYSTEM. THE
CURRENT INTENSITY IS BASED ON A JTWC DVORAK ESTIMATE OF T2.5 USING
THE SUB-TROPICAL TECHNIQUE AND SUPPORTED BY AN ADT ESTIMATE.
INITIAL WIND RADII BASIS: PERSISTENCE.
CURRENT STEERING MECHANISM: THE SOUTHWESTERN PERIPHERY OF THE
LOW-TO-MID LEVEL REFLECTION OF STRONG SUB-TROPICAL RIDGE (STR)
ANCHORED OVER THE DATELINE.
POLEWARD.
AGENCY DVORAK AND AUTOMATED FIXES:
   PGTW: T2.5 - 35 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T1.0 - 25 KTS
   CIMSS ADT: 31 KTS AT 232340Z
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 ARE IMPEDING
INTENSIFICATION.
ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 AND
NOT EXPECTED TO CHANGE INTO A WARM CORE BAROTROPIC (TYPICAL
TROPICAL) SYSTEM. IT WILL NOT DEVELOP INTO A VIGOROUS STORM AND IS
NOT EXPECTED TO REACH 50 KNOTS DURING ITS LIFE CYCLE. THE SYSTEM
WILL MANANGE TO 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, WHILE THE HIGH LATITUDE OF FORMATION PRECLUDES
MOVEMENT THROUGH A ZONE WITH ADEQUATE SEA SURFACE TEMPERATURES BUT
LOW OCEAN HEAT CONTENT. THE POINT OF RECKONING IN THE FORECAST WILL
COME AS THE STORM CROSSES THE 30TH LATITUDE, WHERE IT A BUILDING
SUBTROPICAL RIDGE WILL FORCE THE THE STORM TO TURN TO A WESTWARD
TRACK TOWARDS HONSHU. AS THE STORM MAKES THE TURN, 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.
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 72 HOUR FORECAST POSITION,
HOWEVER, THERE IS A
WIDE SPREAD IN THE GUIDANCE. SOME VORTEX TRACKERS INDICATE LANDFALL
AS FAR SOUTH AS THE CHIBA PENINSULA, WHILE THE NORTHERNMOST
TRACKERS POINT TO MISAWA. 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 JTWC FORECAST STAYS
CLOSE TO THE MULTI-MODEL CONSENSUS, WHICH POINTS TO SENDAI.
THE INTENSITY FORECAST STAYS TO THE HIGH SIDE OF GUIDANCE.
STATISTICAL-DYNAMICAL PREDICTIONS SHOW TOO MUCH VERTICAL WIND SHEAR
AND GIVE UP ON THE SYSTEM BEFORE LANDFALL WHILE CONSENSUS SHOWS A
PEAK AT TAU 24 AS THE STORM BEGINS THE TURN TO THE WEST.  THERE IS
LOW BUT INCREASING CONFIDENCE THAT THE STORM WILL STAY AT LOW
TROPICAL STORM OR TROPICAL DEPRESSION STRENGTH UNTIL LANDFALL AND
WILL DISSIPATE QUICKLY OVER THE RUGGED TERRAIN OF THE JAPANESE
ALPS. IT IS NOT EXPECTED TO SURVIVE INTO THE SEA OF JAPAN.
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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