WDPN31 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (KULAP) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.7N 141.6E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 408 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A PARTIALLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) DISPLACED JUST TO THE
SOUTH OF FLARING DEEP CONVECTIVE BURSTS. BY AROUND THE 0700Z HOUR
THE MSI SUGGESTS THE LLCC MAY BE TUCKING BACK UP UNDER THE
STRONGEST OF THE CONVECTIVE BURSTS. A 270624Z SSMIS 37GHZ MICROWAVE
IMAGE SHOWED A BROAD BAND OF DEEP CONVECTION WRAPPING CYCLONICALLY
INTO A WELL-DEFINED CENTER, THOUGH NOT WRAPPING ALL THE WAY AROUND
ENOUGH TO CALL IT A MICROWAVE EYE FEATURE. BASED ON THE HIGH
CONFIDENCE INITIAL POSITION, THE SYSTEM HAS SLOWED DOWN AS IT HAS
REACHED THE AXIS OF THE STEERING RIDGE AND HAS BEGUN TO TRACK NORTH
OR SLIGHTLY NORTH-NORTHEAST. THE INITIAL INTENSITY IS ASSESSED WITH
MEDIUM CONFIDENCE AT 50 KNOTS, BASED ON THE AVERAGE OF THE AGENCY
DVORAK CURRENT INTENSITY ESTIMATES AND THE SATELLITE CONSENSUS
(SATCON), WHICH ALSO ALIGNS WELL WITH THE EXPERIMENTAL CIMSS DEEP
MICRONET ESTIMATE OF 49 KNOTS AND AN OPEN-AIIR ESTIMATE OF 53 KTS.
THE SYSTEM LIES IN A MARGINAL ENVIRONMENT CHARACTERIZED BY WARM
SSTS (28-29C) AND ROBUST POLEWARD OUTFLOW COMPETING WITH STRONG
SOUTHERLY VERTICAL WIND SHEAR (VWS). MID-LEVEL DRY AIR IS ALSO
BEGINNING TO NOSE ITS WAY IN ON THE SOUTH-SOUTHEAST SIDE OF THE
INNER CORE, INHIBITING CONVECTION THERE AND GIVING THE SYSTEM THE
LOOK OF A MID-LATITUDE FRONTAL TYPE SYSTEM. BUT LOOKS CAN BE
DECEIVING, AS SOUNDER PROFILES AND PHASE-SPACE DIAGRAMS CONFIRM THE
SYSTEM IS STILL SOLIDLY A WARM-CORE TROPICAL CYCLONE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: NORTHWESTERLY 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: T3.5 - 55 KTS
   CIMSS SATCON: 50 KTS AT 270334Z
   CIMSS ADT: 39 KTS AT 270540Z

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 ON THE
SOUTH-SOUTHEAST PERIPHERY. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: HAVING REACHED THE STEERING RIDGE AXIS,
TROPICAL STORM 19W (KULAP) HAS BEGUN TO SHIFT OVER TO A
NORTHEASTWARD TRACK OVER THE PAST FEW HOURS. THIS TREND WILL
CONTINUE AS THE SYSTEM MOVES NORTH OF THE RIDGE AXIS AND
ACCELERATE NORTHEASTWARD ALONG THE WESTERN SIDE OF THE STEERING
RIDGE. WHILE THE OVERALL ENVIRONMENT WOULD SUGGEST WEAKENING DUE TO
THE HIGH SHEAR, THE FORECAST CALLS FOR INTENSIFICATION THROUGH THE
FORECAST PERIOD, FOR TWO PRIMARY REASONS; FIRST THE VERY ROBUST
OUTFLOW ALOFT IS ENOUGH TO OFFSET THE SHEAR, AT LEAST IN THE
NEAR-TERM AS THE RELATIVE SHEAR IS A BIT LOWER DUE TO THE STORM MOTION 
AND SHEAR VECTOR BEING IN PHASE. SECONDLY, BY AROUND TAU 24 TO 36, AS 
THE SYSTEM MOVES NORTHEASTWARD, IT WILL BEGIN TO INTERACT AND COME IN 
PHASE WITH A STRONG 500MB SHORTWAVE TROUGH, WHICH WILL INDUCE
STRONG POSITIVE VORTICITY OVER TOP OF THE SYSTEM, AS WELL AS
ENHANCED THERMAL ADVECTION LEADING TO STRONG BAROCLINIC FORCING AND
INTENSIFICATION AS THE SYSTEM BEGINS EXTRATROPICAL TRANSITION
(ETT). AS INDICATED BY PHASE-SPACE DIAGRAMS AND GLOBAL MODEL
FIELDS, TS 19W WILL REMAIN A WARM-CORE SYSTEM AS IT TRANSITIONS,
BECOMING AN INSTANT WARM-SECLUSION TYPE EXTRATROPICAL LOW BY TAU
48, WHICH WILL LIKELY CONTINUE TO INTENSIFY EVEN AFTER COMPLETION
OF ETT (AND THE END OF THE FORECAST) AS IT MOVES INTO THE BERING
SEA BY AROUND TAU 72. 

MODEL DISCUSSION: TRACK GUIDANCE IS IN VERY GOOD AGREEMENT WITH
MINIMAL SPREAD IN THE CONSENSUS MEMBERS THROUGH THE FORECAST
PERIOD, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.
INTENSITY GUIDANCE IS MIXED, WITH THE COAMPS-TC (BOTH NAVGEM AND
GFS VERSIONS) AND GFS INDICATING NEAR-RAPID INTENSIFICATION THROUGH
TAU 24, PEAKING AT 77 KNOTS, WHILE THE REMAINDER OF THE GUIDANCE
INDICATES A LESS-ROBUST RATE OF INTENSIFICATION, WITH PEAKS BETWEEN
55-65 KNOTS. HWRF SHOWS A DELAYED PEAK INTENSITY OF 65 KNOTS AT TAU
72. THE JTWC FORECAST LIES NEAR THE CONSENSUS MEAN WITH MEDIUM
CONFIDENCE, THROUGH THE FORECAST PERIOD. ADDITIONAL INTENSIFICATION
IS POSSIBLE BEYOND THE END OF THE FORECAST PERIOD AS THE SYSTEM
RAPIDLY MOVES NORTHEAST INTO THE BERING SEA. 

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