WDPN31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (KULAP) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.8N 142.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 361 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A TIGHT
LOW LEVEL CIRCULATION CENTER (LLCC) OCCASIONALLY PEAKING OUT FROM
UNDER CYCLING CONVECTION. THE CENTER WAS RELATIVELY DEVOID OF DEEP
CONVECTION AT THE 1200Z HOUR, BUT SUBSEQUENT IMAGERY REVEALS
ANOTHER ROUND OF CONVECTION HAS FLARED UP TO THE WEST OF THE CENTER
BUT IT REMAINS TO BE SEEN IF THIS CAN MOVE UPSHEAR AND COVER UP THE
LLCC ONCE AGAIN. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON AMBIGUITY ANALYSIS USING A FORTUITOUS 271121Z
ASCAT-B PASS AND THE ANIMATED SHORTWAVE INFRARED SATELLITE IMAGERY. 
THE INITIAL INTENSITY REMAINS ASSESSED AT 50 KNOTS WITH HIGH
CONFIDENCE, HEDGED SLIGHTLY ABOVE THE AGENCY CURRENT INTENSITY
ESTIMATES IN LINE WITH THE SATCON ESTIMATE. ADDITIONAL SUPPORT FOR
THE INITIAL INTENSITY CAME FROM ANALYSIS OF THE WIND FIELD OBSERVED
THE SCATTEROMETER DATA, WITH 45 KNOT WIND BARBS TO THE WEST AND 50
KNOT WIND BARBS INDICATED TO THE EAST SIDE OF THE CIRCULATION. THE
OVERALL ENVIRONMENT IS MARGINALLY FAVORABLE WITH WARM SSTS AND VERY
STRONG POLEWARD OUTFLOW BEING OFFSET BY STRONG VERTICAL WIND SHEAR
AND ENTRAINMENT OF MID-LEVEL DRY AIR WRAPPING INTO THE CORE FROM
THE SOUTH.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 49 KTS AT 271119Z
   CIMSS ADT: 39 KTS AT 271140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 25-30 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR INTRUSION FROM THE SOUTHEAST.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: HAVING ROUNDED THE RIDGE AXIS A FEW HOURS AGO,
TS 19W HAS ALMOST DOUBLED ITS TRACK SPEED, UP TO 14 KNOTS NOW, AS
IT RACES NORTHEASTWARD ALONG THE WEST SIDE OF THE STEERING RIDGE TO
THE EAST. THIS TREND IS EXPECTED TO CONTINUE, WITH THE SYSTEM
STEADILY ACCELERATING TO THE NORTHEAST AS A DEEP SHORTWAVE TROUGH
CURRENTLY ACROSS NORTHERN CHINA BEGINS TO ERODE AND FLATTEN THE
STEERING RIDGE TO THE EAST. THE BIGGEST CONCERN WITH TS 19W IS NOT
THE TRACK WHICH IS PRETTY FIRM, BUT THE INTENSITY AND TIMING OF THE
EXTRATROPICAL TRANSITION. THE SHORTWAVE CURRENTLY OVER NORTHERN
CHINA IS AT PRESENT FAIRLY WEAK, BUT AS TS 19W MOVES NORTHWARD AND
BEGINS TO PUMP WARM AIR UP INTO THE HIGHER LATITUDES, THE
DOWNSTREAM RIDGE AMPLIFIES SIGNIFICANTLY, ALLOWING FOR THE TROUGH
TO DEEPEN SIMULTANEOUSLY. SO MUCH SO THAT BY TAU 36 THE TROUGH HAS
BECOME NEGATIVELY TILTED AND BEGINS TO PICK UP TS 19W AS IT RACES
POLEWARD, MARKING THE START OF EXTRATROPICAL TRANSITION (ETT). THE 
SYSTEM WILL VERY RAPIDLY UNDERGO ETT (WITHIN 24 HOURS) AND BECOME AN 
INSTANT WARM SECLUSION TYPE EXTRATROPICAL LOW, RETAINING ITS WARM CORE 
ALL THE WAY UNTIL IT REACHES THE BERING SEA. IN THE NEAR-TERM THE 
SYSTEM IS EXPECTED TO CONTINUE TO INTENSIFY AS THE STRONG SHEAR IS 
OFFSET DUE TO THE IN-PHASE TRACK MOTION, ALLOWING FOR THE SYSTEM TO 
TAP INTO THE FULL EFFECTS OF THE VERY STRONG DIVERGENT OUTFLOW ALOFT. 
AFTER TAU 24, THE STRONG BAROCLINIC FORCING ASSOCIATED WITH THE 
NEGATIVELY TILTED 500MB TROUGH WILL ALLOW THE SYSTEM TO CONTINUE TO 
INTENSIFY EVEN AS IT TRANSITIONS TO AN EXTRATROPICAL LOW, REACHING
A PEAK OF 70 KNOTS AS IT COMPLETES THE ETT PROCESS.   

MODEL DISCUSSION: TRACK GUIDANCE IS IN TIGHT AGREEMENT THROUGH TAU
24, THOUGH THE GUIDANCE SPREADS OUT TO A 215NM ENVELOPE BY TAU 48
AS THE SYSTEM GOES EXTRATROPICAL. ALONG-TRACK SPREAD IS ABOUT 250NM
AT TAU 48, NOT ALL THAT BAD FOR A RAPIDLY MOVING SYSTEM BECOMING
EXTRATROPICAL. OVERALL CONFIDENCE REMAINS HIGH, AND THE JTWC TRACK
LIES CLOSE TO THE CONSENSUS MEAN THROUGH THE FORECAST PERIOD.
INTENSITY GUIDANCE REMAINS MIXED, WITH THE MESOSCALE MODELS SUCH AS
HWRF AND COAMPS-TC (NAVGEM VERSION) AND THE CONSENSUS MEAN PEAKING
AT 70 KNOTS. THE SHIPS GUIDANCE REMAINS LOW IN THE 55 KNOT RANGE,
WHILE THE COAMPS-TC (GFS VERSION) TAKES THE SYSTEM TO NEAR 95 KNOTS
BY TAU 48. THE JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN
THROUGH THE FORECAST WITH MEDIUM CONFIDENCE. 

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