WDPN31 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (MEKKHALA) WARNING NR 
034//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 31.6N 133.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 394 NM WEST-SOUTHWEST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 26 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS DEEP
CONVECTION PERSISTING OVER THE EASTERN SEMICIRCLE OF A PARTIALLY
EXPOSED, ELONGATED LOW LEVEL CIRCULATION CENTER (LLCC). THE
HIMAWARI-9 GEOSTATIONARY SATELLITE SENSORS ARE DETECTING HUNDREDS
OF LIGHTNING STRIKES AND CLOUD TOPS AS COLD AS -80 DEGREES CELSIUS.
A 270004Z ASCAT PASS REVEALED 35 KT WINDS AND A LESS SYMMETRIC WIND
FIELD. ENVIRONMENTAL CONDITIONS ARE MARGINALLY FAVORABLE FOR
DEVELOPMENT, CHARACTERIZED BY MODERATE VERTICAL WIND SHEAR (VWS)
OFFSET BY 26-27 DEGREE CELSIUS SEA SURFACE TEMPERATURE (SST)
ASSOCIATED WITH THE KUROSHIO CURRENT AND STRONG POLEWARD OUTFLOW
ALOFT. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED
ON THE PARTIALLY EXPOSED LLCC ON THE MSI AND THE AFOREMENTIONED
ASCAT PASS. THE INITIAL INTENSITY IS SET AT 35 KTS WITH HIGH
CONFIDENCE BASED ON THE SAME ASCAT PASS, WHICH IS CLOSE TO THE
CIMSS OBJECTIVE ESTIMATES RANGING FROM 31 KTS TO 41 KTS AND
SUBJECTIVE DVORAK FIXES OF T2.0-2.5.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: DEEP-LAYER WESTERLY FLOW

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T1.5 - 25 KTS
   CIMSS SATCON: 36 KTS AT 262000Z
   CIMSS ADT: 33 KTS AT 270110Z
   CIMSS AIDT: 41 KTS AT 270110Z
   CIMSS D-MINT: 34 KTS AT 262236Z
   CIMSS D-PRINT: 31 KTS AT 270010Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 07W CONTINUES TO ACCELERATE ON
A NORTHEASTWARD TRAJECTORY, DRIVEN BY DEEP-LAYER WESTERLY FLOW ON
THE POLEWARD SIDE OF THE SUBTROPICAL RIDGE. MEKKHALA JOGGED TO THE
NORTH FROM 261800Z TO 270000Z, WHICH NECESSITATED A POLEWARD SHIFT
IN THE TRACK AND RESULTED IN A CLOSER APPROACH TO THE KANTO PLAIN.
THE SYSTEM IS GRADUALLY GAINING EXTRATROPICAL CHARACTERISTICS, WITH
CONVECTION CONFINED TO THE NORTH AND EAST OF THE CENTER AND
INCREASING TEMPERATURE ADVECTION. DATA FROM THE 270004Z ASCAT PASS
INDICATED THAT MAXIMUM SUSTAINED WINDS ARE ON THE CUSP OF REACHING
40 KTS. 07W IS TAPPING INTO THE FAVORABLE REGION OF A 125-KT JET
STREAK OVER NORTHERN HONSHU. THE RESULTING DIVERGENCE ALOFT HAS
ENABLED TO CONVECTION TO INCREASE IN COVERAGE AND VIGOR. AS SUCH,
THE FORECAST STILL CALLS FOR THE TROPICAL STORM TO ATTAIN 40 KTS AT
TAU 12 BEFORE THE INCREASING VWS AND COOLER SST MORE THAN OFFSET
THE GAINS FROM THE ENHANCED VENTILATION ALOFT. AS THE SYSTEM MAKES
A CLOSE APPROACH TO THE KANTO PLAIN, THE STRONGEST WINDS WILL
REMAIN OFFSHORE. THE PREDICTED 35-45 KTS OF VWS AT TAU 24 AND TAU
36 WILL INDUCE WEAKENING AS MEKKHALA COMPLETES EXTRATROPICAL
TRANSITION. THE GALE-FORCE WIND RADII WILL EXPAND DUE TO BAROCLINIC
FORCING.

MODEL DISCUSSION: MODELS ARE TIGHTLY CLUSTERED THROUGHOUT THE
FORECAST PERIOD WITH A CROSS-TRACK SPREAD OF 40 NM AT TAU 12.
BECAUSE OF THE NORTHWARD JOG IN THE PAST SIX HOURS, SEVERAL
TRACKERS NOW DEPICT LANDFALL OVER THE KANTO PLAIN, INCLUDING
HAFS-A, HWRF, THE MEAN OF THE UKMET AND GEFS ENSEMBLES, AND NAVGEM.
THE GFS AND THE AI MODELS REMAIN OFFSHORE. THE JTWC TRACK FORECAST
IS LAID NEAR THE MULTI-MODEL CONSENSUS AT TAU 12 AND THEN HEDGES
CLOSER TO THE GFS MODEL WITH HIGH CONFIDENCE. THE INTENSITY
FORECAST MIRRORS THE GFS SOLUTION IN SHOWING SLIGHT INTENSIFICATION
AT TAU 12 FOLLOWED BY SLOW WEAKENING WITH MEDIUM CONFIDENCE. HAFS-A
AND COAMPS-TC WEAKEN THE SYSTEM FROM THE BEGINNING, THOUGH THESE
SOLUTIONS APPEAR LESS LIKELY GIVEN THE EXPANDING COVERAGE OF DEEP
CONVECTION.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM//
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