****0000006244****
WDPN32 PGTW 270900

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//

SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (JEBI) WARNING NR

004//

RMKS/

1. FOR METEOROLOGISTS.

2. 6 HOUR SUMMARY AND ANALYSIS.



SUMMARY:

   INITIAL POSITION: 18.3N 144.8E

   INITIAL INTENSITY: 35 KTS

   GEOGRAPHIC REFERENCE: 436 NM SOUTH-SOUTHEAST OF IWO TO

   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 07 KTS

   SIGNIFICANT WAVE HEIGHT: 15 FEET



SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:

ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A

DISORGANIZED SYSTEM, STRUGGLING AGAINST PERSISTENT MODERATE

MID-LEVEL SHEAR. THE MSI REVEALS A FULLY EXPOSED LOW LEVEL

CIRCULATION CENTER (LLCC) DISPLACED TO THE NORTHWEST OF

DISORGANIZED FLARING CONVECTION OVER THE NORTHERN MARIANAS ISLANDS.

RECENT SCATTEROMETER DATA FROM 260330Z SHOWS A WELL-DEFINED,

SYMMETRICAL CIRCULATION CENTER. HOWEVER, THE WIND FIELD REMAINS

HIGHLY ASYMMETRICAL, WITH LIGHT WINDS OF LESS THAN 20 KNOTS ACROSS

THE ENTIRETY OF THE WESTERN HEMISPHERE OF THE CIRCULATION, WHILE

WINDS BETWEEN 30-35 KNOTS ARE EVIDENT ACROSS THE EASTERN

HEMISPHERE. THE INITIAL POSITION WAS ASSESSED WITH HIGH CONFIDENCE

BASED ON THE EXPOSED LLCC IN THE MSI. THE INITIAL INTENSITY WAS

ASSESSED WITH MEDIUM CONFIDENCE, HEDGED SLIGHTLY HIGHER THAN THE

AGENCY DVORAK ESTIMATES, BUT IN LINE WITH THE CIMSS OBJECTIVE

ESTIMATES LISTED BELOW. ANIMATED WATER VAPOR IMAGERY AS WELL AS

MESOSCALE MODELS INDICATE THE PRESENCE OF A DEEP POCKET OF DRY AIR

WHICH BASICALLY COVERS THE WESTERN HALF OF THE CIRCULATION.

ADDITIONALLY, THE WATER VAPOR IMAGERY SHOWS A TUTT-CELL SITUATED

ABOUT 400NM NORTHEAST, IN A VERY UNFAVORABLE POSITION, AS IT IS

LEADING TO CONVERGENT NORTHERLY FLOW OVER THE LLCC AND ENHANCING

SHEAR. THE COMBINATION OF THESE FACTORS, ALONG WITH RELATIVELY WEAK

UPPER-LEVEL OUTFLOW, ARE GENERATING A MARGINAL TO MARGINALLY

UNFAVORABLE ENVIRONMENT FOR TS 19W. THE SYSTEM IS TRACKING

NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF A DEEP-LAYER

SUBTROPICAL RIDGE (STR) TO THE NORTHEAST.



INITIAL WIND RADII BASIS: PERSISTENCE



CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER

STR CENTERED TO THE NORTHEAST.



AGENCY DVORAK AND AUTOMATED FIXES:

   PGTW: T2.5 - 35 KTS

   RJTD: T2.0 - 30 KTS

   KNES: T2.0 - 30 KTS

   CIMSS SATCON: 36 KTS AT 270330Z

   CIMSS ADT: 37 KTS AT 270530Z

   CIMSS AIDT: 36 KTS AT 270600Z

   CIMSS DPRINT: 36 KTS AT 270600Z

   CIMSS DMINT: 29 KTS AT 270700Z



FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL

   VWS: 5-10 KTS

   SST: 29-30 CELSIUS

   OUTFLOW: MODERATE EQUATORWARD

   OTHER FACTORS: DEEP POCKET OF DRY AIR ENTRENCHED OVER THE

WESTERN HALF OF THE CIRCULATION. TUTT-CELL POSITIONED TO THE

NORTHEAST.



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: TS 19W IS FORECAST TO CONTINUE TRACKING

NORTHWESTWARD ALONG THE SOUTHWEST SIDE OF THE STEERING RIDGE FOR

THE NEXT 48 HOURS. THE LATEST GFS AND ECMWF GLOBAL FIELDS SUGGEST

THE DEEP LAYER STR HAS BUILT TOWARDS THE SOUTHWEST OVER THE PAST

DAY, NOW EXTENDING SOUTHWESTWARD FROM THE RIDGE CENTER ALL THE WAY

TO OKINAWA. THE VORTEX TRACKERS HAVE NOT YET PICKED UP ON THIS AND

ARE PERSISTING IN TAKING TS 19W STRAIGHT NORTHWESTWARD, BUT FURTHER

WALKING OF THE TRACK TO A MORE WEST-NORTHWEST TRACK IS NOT OUT OF

THE REALM OF THE POSSIBLE. REGARDLESS, BY TAU 48, THE RIDGE

EXTENSION IS EXPECTED TO QUICKLY BREAK DOWN, ALLOWING TS 19W TO

ROUND THE RIDGE AXIS AND ACCELERATE NORTH, THEN NORTHEASTWARD

THROUGH THE REMAINDER OF THE FORECAST PERIOD. IN TERMS OF

INTENSITY, THE PESKY TUTT-CELL TO THE NORTHEAST WILL CONTINUE TO

TRACK SLOWLY WESTWARD, BUT REMAIN IN AN UNFAVORABLE POSITION

RELATIVE TO TS 19W FOR THE NEXT 24-36 HOURS. SHEAR IS EXPECTED TO

INCREASE SHARPLY IN THE NEXT 12 HOURS, WHICH WHEN COMBINED WITH THE

DRY AIR ALOFT, WILL LEAD TO A PERIOD OF WEAKENING THROUGH TAU 24.

BY TAU 36, THE TUTT IS EXPECTED TO WEAKEN AND PASS TO THE WEST SIDE

OF TS 19W, WHICH WILL OPEN UP A POLEWARD OUTFLOW CHANNEL AND AS WELL

BE ENHANCED FURTHER AFTER TAU 72 BY VENTILATION INTO A JET

STREAK OVER JAPAN. AT THE SAME TIME AS THE TUTT-CELL MOVES WEST OF

THE SYSTEM, THE ATMOSPHERE IS EXPECTED TO MOISTEN SIGNIFICANTLY AND

AS AN UPPER-LEVEL POINT SOURCE DEVELOPS ALOFT, SHEAR IS FORECAST TO

WEAKEN. THESE FACTORS TAKEN TOGETHER WILL ALLOW THE SYSTEM TO

INTENSIFY UP TO A PEAK OF AT LEAST 60 KNOTS BY TAU 96. AFTER THIS

POINT, THE SYSTEM BEGINS EXTRATROPICAL TRANSITION AS IT MOVES INTO

THE BAROCLINIC ZONE, DEVELOPS FRONTAL CHARACTERISTICS, AND MOVES

UNDER A STRONG JET STREAK. THE SYSTEM IS EXPECTED TO COMPLETE ETT

BY TAU 120 TO THE EAST OF HOKKAIDO.



MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN FAIRLY GOOD

AGREEMENT, THOUGH THERE ARE THE FIRST HINTS OF A BIT OF A SPLIT IN

THE GUIDANCE BEGINNING AT TAU 36, WHERE THE GFS AND RELATED MODELS

TURN THE SYSTEM SHARPLY NORTHWARD, TRACKING CLOSE TO IWO TO. THE

REMAINDER OF THE GUIDANCE INCLUDED THE ECMWF AND NAVGEM, GALWEM AND

UKMET TAKE THE SYSTEM ON A MORE WEST-NORTHWEST TRACK, ON A WIDER

RECURVE. CROSS-TRACK SPREAD BETWEEN OUTLIERS IS 220NM AT TAU 72,

INCREASING TO ABOUT 250NM AT TAU 120. ALONG-TRACK SPREAD INCREASES

SHARPLY AFTER THE SYSTEM ROUNDS THE RIDGE AXIS, UP TO 1000NM

BETWEEN THE NAVGEM AND GFS BY THE END OF THE FORECAST PERIOD. THE

JTWC FORECAST IS A BIT WIDER ON THE RECURVE THAN THE GFS BUT NOT AS

FAR AS THE NAVGEM AND ECMWF. IN THE EXTENDED FORECAST, THE JTWC

TRACK IS ROUGHLY BETWEEN THE FASTEST GFS AND THE CONSENSUS MEAN.

INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL

STAGNANT OR WEAKEN SLIGHTLY FOR THE FIRST 24 HOURS, FOLLOWED BY

STEADY INTENSIFICATION TO A PEAK BETWEEN 60 KNOTS AND 75 KNOTS.



FORECAST CONFIDENCE:

   TRACK 0 - 72 HR: MEDIUM

   TRACK 72-120 HR: LOW

   INTENSITY 0 - 72 HR: MEDIUM

   INTENSITY 72-120 HR: MEDIUM//

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