WDPN31 PGTW 030300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (MUN) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 27.0N 145.4E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 577 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 04W (MUN) HAS UNDERGONE A RATHER REMARKABLE
TRANSFORMATION OVER THE LAST SIX HOURS. AT THE PREVIOUS FORECAST
TIME, THE LOW LEVEL CIRCULATION CENTER (LLCC) WAS JUST BEGINNING TO
TUCK UNDER RECENTLY DEVELOPED CONVECTION. BASED ON A SERIES OF
MICROWAVE IMAGES FROM THE COWVR AND WSF-M INSTRUMENTS, THE LLCC
APPEARS TO HAVE UNDERGONE A PRECESSION, AS VORTEX AXISYMMETRIZED
UNDER THE CONVECTIVE REGION. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY INDICATES THE CONVECTION HAS WARMED SIGNIFICANTLY
OR DISSIPATED ALL TOGETHER IN THE PAST COUPLE OF HOURS, LEAVING A
HOW MOSTLY EXPOSED LLCC, WITH POCKETS OF REFORMING DEEP CONVECTION.
THE UPPER-LEVEL STRUCTURE IS COMPLEX BASED ON CIRA UPPER-LEVEL
DERIVED MOTION VECTORS (ULDMV), SHOWING AN ANTICYCLONIC ARC OF
OUTFLOW PUSHING SOUTH, THEN TURNING POLEWARD ALONG THE WESTERN
EXTENT OF THE CIRCULATION. MEANWHILE UPPER-LEVEL FLOW IS CYCLONIC
ALONG THE EASTERN SIDE OF THE VORTEX UNTIL REACHING A POINT NORTH
OF 30N WHERE IT TURNS ANTICYCLONICALLY. THE CIRA ADVECTED LAYER
PRECIPITABLE WATER PRODUCT DEPICTS A WEDGE OF DEEP, DRY AIR MOVING
UP FROM THE SOUTH AND WRAPPING ALL THE WAY AROUND THE VORTEX,
ENCROACHING INTO THE INNER-CORE.  OVERALL, THE ENVIRONMENT IS
FAVORABLE, WITH WARM SSTS, GOOD OUTFLOW ALOFT AND LOW VWS, THOUGH
OFFSET SOMEWHAT BY THE INFLUENCE OF THE DRY AIR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF AN EXTENSIVE
RIDGING PATTERN EXTENDING FROM EAST OF THE PHILIPPINES, OVER THE
MARIANAS ISLANDS AND THEN NORTHEASTWARD TO NEAR 35N 175E. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS SATCON: 46 KTS AT 030000Z
   CIMSS ADT: 35 KTS AT 030000Z
   CIMSS AIDT: 39 KTS AT 030000Z
   CIMSS D-MINT: 33 KTS AT 022052Z
   CIMSS D-PRINT: 37 KTS AT 030030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR WRAPPING INTO THE CORE OF THE
SYSTEM.

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: DUE TO VORTEX PRECESSION, TS 04W HAS SLOWED
CONSIDERABLY OVER THE PAST SIX HOURS. NOW THAT THE VORTEX APPEARS
TO BE VERTICALLY ALIGNED, THE SYSTEM WILL BEGIN TO ACCELERATE
TOWARDS THE NORTH-NORTHWEST IN THE NEAR-TERM, ALONG THE WESTERN
SIDE OF THE STEERING RIDGE TO THE EAST. BY TAU 36, THE SOUTHWESTERN
END OF THE LARGE RIDGING PATTERN BREAKS OFF INTO A DISTINCT
SUBTROPICAL RIDGE (STR) CENTER OVER THE NORTHERN MARIANAS. AS THIS
STR BUILDS AND EXPANDS IN AREAL COVERAGE, IT WILL BECOME THE
DOMINANT STEERING INFLUENCE OF TS 04W, WHICH WILL TURN ONTO A MORE
EAST-NORTHEASTWARD TRACK BETWEEN TAU 36 AND TAU 72. BEYOND TAU 72,
THE SYSTEM WILL TURN NORTHWARD, TRAVERSING ALONG THE WESTERN SIDE
OF A DEVELOPING REX BLOCK SETTING UP ALONG 165E. AFTER TAU 96, TS
04W WILL ACCELERATE INTO A DEVELOPING BREAK IN THE RIDGE TO THE
NORTH. IN TERMS OF INTENSITY, THE SYSTEM HAS ENJOYED A BRIEF SPURT
OF INTENSIFICATION DUE TO THE VORTEX ALIGNMENT. HOWEVER, THE
INFLUENCE OF DRY AIR ON THE INNER-CORE WILL PUT A BRAKE ON THE
INTENSIFICATION TREND IN THE NEAR-TERM. UNTIL THE CONVECTION CAN
PERSIST IN AND AROUND THE CORE AND PUSH THE DRY AIR OUT, THE SYSTEM
WILL INTENSIFY AT A SLOW BUT STEADY RATE. THIS PROCESS SHOULD BE
WRAPPED UP AROUND TAU 36, AT WHICH POINT, THE SYSTEM WILL ALSO TAP
INTO AN ENHANCED POLEWARD OUTFLOW CHANNEL ON THE SOUTHEAST SIDE OF
AN UPPER-LEVEL TROF APPROACHING FROM THE NORTHWEST. THIS WILL ALLOW
FOR ANOTHER BURST OF MORE PROLONGED INTENSIFICATION THROUGH TAU 72.
A SHARP INCREASE IN SHEAR IS ANTICIPATED TO HIT THE SYSTEM BETWEEN
TAU 72 AND 96, WITH TS 04W LIKELY BEING DECAPITATED AROUND TAU 96,
AS IT ALSO HAPPENS TO CROSS THE 26C ISOTHERM. THE SYSTEM IS
EXPECTED TO REMAIN WARM-CORE EVEN AS IT RAPIDLY SHALLOWS OUT,
BEGINNING SUBTROPICAL TRANSITION (STT) BETWEEN TAU 96-120 AS IT
RAPIDLY WEAKENS. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS BY AND LARGE IN
GOOD AGREEMENT ON THE OVERALL S-TYPE TRACK SCENARIO. THE GALWEM
CONTINUES TO DEPART FROM THE REST OF THE GUIDANCE, IN BEING
SIGNIFICANTLY SLOWER AND THEN TRACKING NORTHWEST TOWARDS HONSHU
AFTER TAU 96. THE HWRF AND HAFS-A (THOUGH NOT MEMBERS OF THE TRACK
CONSENSUS) SHOW A SIMILAR TREND, THOUGH THEY ARE MORE IN LINE WITH
THE REST OF THE GUIDANCE IN TERMS OF SPEED THROUGH TAU 72. THE
REMAINDER OF THE CONSENSUS PACKAGE IS CONFINED TO A 120NM ENVELOPE
THROUGH TAU 72 AND THE JTWC TRACK IS POSITIONED JUST EAST OF THE
CONSENSUS MEAN. AFTER TAU 72, THE MODELS BEGIN TO DISPERSE AND FAN
OUT, WITH THE ECMWF SHOWING THE FURTHEST WEST TRACK, WHILE THE
NAVGEM IS THE FURTHEST TO THE EAST. THE JTWC TRACK IS POSITIONED
JUST EAST OF THE CONSENSUS MEAN. ENSEMBLE GUIDANCE IS ALSO IN
GENERAL AGREEMENT, THOUGH THERE REMAIN FIVE ECEPS MEMBERS AND TEN
GEFS MEMBERS WHICH DEPICT A TRACK TOWARDS HONSHU, THUS THERE IS A
VERY LOW, BUT NON-ZERO, PROBABILITY OF A POTENTIAL WESTWARD TRACK
AFTER TAU 72. INTENSITY GUIDANCE IS MIXED, WITH THE HAFS-A AND HWRF
INDICATING A FLAT OR DECREASING TREND THROUGH TAU 48, THEN A SHARP
INCREASE TO A PEAK BETWEEN 55-70 KNOTS AT TAU 72 FOLLOWED BY RAPID
WEAKENING. THE CTCX MEANWHILE INDICATES SLOW INTENSIFICATION TO TAU
24, THEN RAPID UP TO A PEAK OF 80 KNOTS AT TAU 60. THREE RAPID
INTENSIFICATION (RI) AIDS HAVE TRIPPED (RICN, RIDE AND FRIA) ON
THIS CYCLE, AND THE CTCX ENSEMBLE INDICATES A THIRTY PERCENT
PROBABILITY OF RI IN THE TAU 48-72 TIMEFRAME. THUS, THERE IS A LOW
PROBABILITY OF A NEAR-TERM RI EVENT. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   TRACK 72-120 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: LOW//
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