WDPN32 PGTW 302100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (JEBI) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 30.8N 141.2E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 280 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS TROPICAL
STORM (TS) 19W (JEBI) CONTINUING TO ORGANIZE AND SLOWLY INTENSIFY
AS IT PICKS UP SPEED POLEWARD. THE LATEST EIR SUGGESTS THE EARLY
STAGES OF BANDING EYE DEVELOPMENT AND A SMALL-SCALE UPPER-LEVEL
ANTICYCLONE ALOFT OVER THE SYSTEM REPRESENTED BY TRANSVERSE BANDING
FEATURES, PARTICULARLY EVIDENT ACROSS THE SOUTHERN HEMISPHERE. THIS
IS OF IMPORTANCE, AS THE LATEST CIMSS AND CIRA ATMOSPHERIC MOTION
VECTOR (AMV) DATA ARE NOT DETECTING THIS UPPER-LEVEL OUTFLOW.
ANIMATED WATER VAPOR IMAGERY DEPICTS A STRONG UPPER-LEVEL LOW TO
THE SOUTHWEST OF TS 19W, WHICH IS CURRENTLY ENHANCING THE POLEWARD
OUTFLOW BUT ALSO IMPARTING SOME SOUTHERLY SHEAR ON THE SYSTEM.
LASTLY, SHORTWAVE INFRARED (SWIR) IMAGERY AND EARLIER ASCAT DATA
INDICATED A SURFACE LOW TRACKING SOUTHWESTWARD ABOUT 275NM
NORTHWEST OF TS 19W. DUE TO A LACK OF RECENT HIGH RESOLUTION
MICROWAVE IMAGERY, THE INITIAL POSITION IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON ANALYSIS OF A 301610Z ATMS 88.9GHZ MICROWAVE
IMAGE WHICH REVEALED A WELL-DEFINED BAND OF CONVECTION ACROSS THE
SOUTHERN HEMISPHERE WRAPPING INTO A DEFINED LOW LEVEL CIRCULATION
CENTER (LLCC). THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE, HEDGED HIGHER THAN THE AGENCY FIXES NOTED BELOW IN
LIGHT OF AN ADJUSTED ADT VALUE OF T3.4 AND THE OVERALL IMPROVING
STRUCTURE. THE ENVIRONMENT REMAINS OVERALL FAVORABLE WITH WARM
SSTS, AND ROBUST POLEWARD OUTFLOW. HOWEVER, SOUTHERLY SHEAR IS
BEGINNING TO INCREASE (CURRENTLY ESTIMATED AT 20 KNOTS BY CIMSS)
THOUGH FOR THE IMMEDIATE FUTURE IT LOOKS LIKE THE OUTFLOW IS
OFFSETTING THE SHEAR.

INITIAL WIND RADII BASIS: PERSISTENCE WITH EARLIER SAR DATA. 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST-NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 57 KTS AT 301800Z
   CIMSS ADT: 49 KTS AT 301730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: UPPER-LEVEL LOW TO THE SOUTHWEST; SURFACE LOW TO
THE NORTHWEST. 

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TS 19W IS IN THE AGGREGATE EXPECTED TO
CONTINUE TRACKING POLEWARD, RECURVING TO THE NORTHEAST OVER THE
DURATION OF THE FORECAST PERIOD. MULTIPLE FACTORS HOWEVER HAVE LED
TO A SHIFT IN THE TRACK, BRINGING IT CLOSER TO EASTERN HONSHU.
FIRST, THE SURFACE LOW ABOUT 275NM TO THE WEST-NORTHWEST IS SLIDING
SOUTHWESTWARD BUT ALSO STRENGTHENING AS IT MOVES UNDER THE STRONG
UPPER-LEVEL LOW TO THE SOUTHWEST. AT THE SAME TIME, THE STR TO THE
EAST IS BUILDING AND THE WESTERN PERIPHERY OF IT BECOMING MORE
NORTH-SOUTH ORIENTED. THE COMBINATION OF FACTORS WILL DRIVE TS 19W
ON A MORE NORTHWARD, OR EVEN POSSIBLY SLIGHTLY
NORTH-NORTHWESTWARD, TRACK OVER THE NEXT 12 HOURS, BRING THE
SYSTEM WITHIN LESS THAN 100NM FROM YOKOSUKA. THE EARLIER SAR DATA
CONTINUES TO SHOW THE WIND FIELD REMAINS VERY ASYMMETRIC, WITH THE
BULK OF THE 35KT WINDS, AND THE ENTIRETY OF THE 50KT WINDS CONFINED
TO THE EASTERN SIDE OF THE STORM. THE SYSTEM IS EXPECTED TO REACH
THE RIDGE AXIS BY TAU 12, THEN RAPIDLY ACCELERATE NORTHEASTWARD.
EXTRATROPICAL TRANSITION IS FORECAST TO BEGIN BY TAU 24 AS THE
SYSTEM TRACKS UNDER THE JET AND GAINS FRONTAL CHARACTERISTICS,
COMPLETING ETT BY TAU 36. FOR THE NEXT 12 HOURS OR SO, THE ROBUST
OUTFLOW WILL OFFSET THE INCREASING SHEAR, ALLOWING TS 19W TO
INTENSIFY UP TO MINIMAL TYPHOON STRENGTH. AFTER TAU 12, THE SHEAR
WILL COME TO DOMINATE THE OUTFLOW, WITH THE SYSTEM LIKELY TO BE
DECAPITATED, LEADING TO RAPID WEAKENING AFTER TAU 24 AS THE SYSTEM
UNDERGOES ETT. 

MODEL DISCUSSION: THE CPA TO YOKOSUKA HAS DROPPED FROM 148NM AT
301200Z TO 98NM WITH THUS FORECAST DUE TO THE REASONS OUTLINED
ABOVE. THE MAJORITY OF THE CONSENSUS GUIDANCE PACKAGE (INTERPOLATED
TRACKERS) REMAINS WELL-CONSTRAINED IN A TIGHT CROSS-TRACK ENVELOPE
THAT REMAINS CONSISTENT WITH THE PREVIOUS FORECAST AND KEEPS THE
SYSTEM WELL OFFSHORE. HOWEVER, THE 1200Z RAW GFS AND GEFS TRACKERS
SHOW A SIGNIFICANT SHIFT WESTWARD, BOTH INDICATING A
NORTH-NORTHWEST TRACK THROUGH TAU 12, BEFORE TURNING
NORTH-NORTHEASTWARD AND CLIPPING THE CHIBA PENINSULA BEFORE
REJOINING THE GUIDANCE ENVELOPE. THE BULK OF THE INDIVIDUAL GEFS
MEMBERS REMAIN OFFSHORE, THOUGH THREE MEMBERS DO SKIRT THE CHIBA
PENINSULA. THE LAST ECEPS PACKAGE REMAINS FURTHER OFFSHORE, WITH
ALL MEMBERS CONSTRAINED WITHIN THE CONSENSUS ENVELOPE. THE JTWC
FORECAST TRACK IS SHIFTED WESTWARD, BUT REMAINS EAST OF THE GFS AND
GEFS, GENERALLY ON THE FAR WESTERN EDGE OF THE CONSENSUS ENVELOPE.
INTENSITY GUIDANCE SHOWS A SIGNIFICANT AMOUNT OF INTENSIFICATION,
UP TO A PEAK OF 75-90 KNOTS (COAMPS-TC AND CTR1), WHILE THE HAFS-A
INDICATES A MORE MODEST INTENSIFICATION UP TO 65 KNOTS. THE JTWC
FORECAST LIES CLOSE TO THE HAFS-A THROUGH THE FORECAST PERIOD.   

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