WDPN32 PGTW 030900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (BAILU) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 34.4N 143.6E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 199 NM EAST-SOUTHEAST OF YOKOSUKA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 22 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) CONTINUES TO SHOW A
COMPLEX CIRCULATION WITH AT LEAST TWO MAIN CIRCULATIONS EMBEDDED
WITHIN IT. WEAK CONVECTION CONTINUES TO FLARE UP FROM TIME TO TIME
NEAR THE ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC) BUT SO FAR
HAS NOT PERSISTED MORE THAN A FEW HOURS. A 022339Z ASCAT-B PASS
REVEALED THE COMPLEX NATURE OF THE OF THE CIRCULATION, WITH A LARGE
ROTATION EVIDENT, CENTERED ROUGHLY 135NM SOUTHEAST OF YOKOSUKA.
HOWEVER, THE VORTEX THAT JTWC HAS BEEN TRACKING CONSISTENTLY FOR
THE PAST DAY IS ACTUALLY DEPICTED AS A MUCH SMALLER AREA OF
ROTATION TO THE SOUTHEAST OF THE LARGER ONE, AND MUCH CLOSER TO THE
ENHANCED WIND FIELD ALONG THE SOUTHEASTERN FLANK. SUBSEQUENT
VISIBLE IMAGERY SHOWS THE LARGER ROTATION TRACKING EASTWARD TOWARDS
THE SMALLER ONE AND ULTIMATELY MERGING WITH IT PRIOR TO THE 0600Z
HOUR. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED
ON THE OVERALL COMPLEX NATURE OF THE SYSTEM AND THE OBSCURED
LOW-LEVEL FEATURES. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM
CONFIDENCE BASED IN LARGE PART ON EXTRAPOLATION OF THE EARLIER
ASCAT DATA WHICH SHOWED A SMALL PATCH OF 35 KNOT WINDS IN THE
SOUTHEASTERN QUADRANT. ENVIRONMENTAL CONDITIONS ARE MARGINAL, WITH
ROBUST POLEWARD OUTFLOW, WARM SSTS AND LOW VWS OFFSET BY THE
CONTINUED PRESENCE DRY MID-LEVEL AIR ALONG THE WESTERN FLANK AND
THE MULTIPLE VORTEX, HIGHLY ASYMMETRIC STRUCTURE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.0 - 30 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 49 KTS AT 030610Z
   CIMSS ADT: 39 KTS AT 030530Z
   CIMSS AIDT: 42 KTS AT 030530Z
   CIMSS D-MINT: 27 KTS AT 030343Z
   CIMSS D-PRINT: 27 KTS AT 030530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 5-10 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MULTIPLE VORTICES; DRY MID-LEVEL AIR TO THE WEST
AND SOUTHWEST. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TROPICAL STORM (TS) 13W IS FORECAST TO
CONTINUE TRACKING NORTHEASTWARD OVER THE NEXT 12 HOURS, GRADUALLY
TURNING ONTO AN EASTWARD TRACK AFTER TAU 24 IS THE STEERING RIDGE
SLIDES WESTWARD TO THE SOUTH OF THE SYSTEM. TRACK SPEEDS SLOW DOWN
SIGNIFICANTLY AFTER TAU 36 AS THE STEERING GRADIENT SHARPLY WEAKENS
DUE TO A BREAK IN THE RIDGE TO THE SOUTH. AFTER TAU 48, THE SYSTEM
TURNS NORTHEASTWARD ONCE MORE AS IT COMES UNDER THE STEERING
INFLUENCE OF ANOTHER STR MOVING WESTWARD FROM THE DATELINE. TRACK
SPEEDS INCREASE AFTER TAU 72 AS THE STR MOVES INTO A POSITION SOUTH
OF THE SYSTEM. NO SIGNIFICANT CHANGE IS EXPECTED IN THE INTENSITY
OF THE SYSTEM FOR THE FIRST 72 HOURS OF THE FORECAST, AS
ENVIRONMENTAL CONDITIONS WILL COMPETE AND OFFSET ONE ANOTHER. SHEAR
IS EXPECTED TO REMAIN RELATIVELY LOW AND UPPER-LEVEL OUTFLOW WILL
BE VERY GOOD AS THE SYSTEM STARTS TO PUSH MASS INTO THE REAR OF A
JET MAX MOVES EAST OFF HOKKAIDO. HOWEVER, DECREASING SSTS,
PERSISTENT DRY AIR INTRUSIONS AND THE LACK OF COHESIVE VORTEX
STRUCTURE WILL OFFSET THE OTHERWISE FAVORABLE CONDITIONS, LEADING
TO AN OVERALL STEADY INTENSITY THROUGH TAU 72. BRIEF VARIATIONS
ABOVE AND BELOW THE MEAN INTENSITY CAN BE EXPECTED, ESPECIALLY
THROUGH TAU 36. THE SYSTEM WILL BEGIN EXTRATROPICAL TRANSITION BY
TAU 72, WITH ETT EXPECTED TO BE COMPLETE BY TAU 96. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN TIGHT
AGREEMENT THROUGH TAU 72, WITH A CROSS-TRACK SPREAD OF 110NM, WITH
THE NOTABLE EXCEPTION OF NAVGEM WHICH LIES ABOUT 100NM SOUTH OF THE
SOUTHERN EDGE OF THE GUIDANCE ENVELOPE. ALONG-TRACK SPREAD OPENS UP
TO ABOUT 125NM BY TAU 72. CROSS- AND ALONG-TRACK SPREAD INCREASE AS
THE SYSTEM UNDERGOES ETT AND BY TAU 96 MEASURE 235NM AND 355NM
RESPECTIVELY, WITH THE GFS BEING THE FASTEST AND THE ECMWF ENSEMBLE
MEAN BEING THE SLOWEST MODELS. THE JTWC FORECAST IS POSITIONED
NEAR, BUT SLIGHTLY FASTER THAN, THE MULTI-MODEL CONSENSUS MEAN
THROUGH THE FORECAST PERIOD WITH HIGH CONFIDENCE. INTENSITY
GUIDANCE IS IN FAIRLY GOOD AGREEMENT, WITH ALL BUT THE HAFS-A
INDICATING A VERY SMALL AMOUNT OF INTENSIFICATION (40 KNOTS PEAK)
THROUGH TAU 48, FOLLOWED BY A SHARP WEAKENING THROUGH TAU 96. THE
JTWC FORECAST IS PLACED NEAR THE HAFS-A TO TAU 72, THEN REJOINS THE
PACK THEREAFTER. 

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM//
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