WDPN32 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (SHANSHAN) WARNING NR 
006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.5N 140.8E
   INITIAL INTENSITY: 50 KTS
   GEOGRAPHIC REFERENCE: 329 NM NORTHWEST OF ANDERSEN AFB
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
STORM 11W (SHANSHAN) WITH A CONTINUED AND RELATIVELY LARGE CENTRAL
DENSE OVERCAST (CDO) OBSCURING THE LOW-LEVEL CYCLONIC CIRCULATION
(LLCC). THE SYSTEM HAS BEGUN TO TRACK NORTHWARD OVER THE LAST FEW
HOURS AT 05 KTS, WHILE CENTRAL CONVECTION HAS PERSISTED VIGOROUSLY
OVER THE ASSESSED CENTER. WITH WARM SEA SURFACE TEMPERATURES (28-30
C), LOW TO MODERATE VERTICAL WIND SHEAR (15-20 KTS), AND
DUAL-CHANNEL UPPER-LEVEL OUTFLOW, THE ENVIRONMENT REMAINS CONDUCIVE
FOR FURTHER INTENSIFICATION. THE INITIAL POSITION IS PLACED WITH
LOW CONFIDENCE AS THE LLC HAS REMAINED OBSCURED BY THE
AFOREMENTIONED CDO, HOWEVER, AN EARLIER (221438Z) OCEANSAT-3 IMAGE
HAS CONFIRMED THE SYSTEM'S NORTHWARD TRACK, WITH AN ASSOCIATED
ASYMETRIC WIND FIELD. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE OBJECTIVE AND SUBJECTIVE
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: THE PERIPHERY OF A SOUTHWESTWARD
EXTENDING RIDGE FROM THE DEEP-LAYER SUBTROPICAL RIDGE TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 49 KTS AT 221309Z
   CIMSS ADT: 53 KTS AT 221900Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 11W IS FORECAST TO REMAIN IN A WEAK
STEERING PATTERN OVER THE NEXT 6-12 HOURS AS RIDGING FROM THE EAST
CONTINUES TO BUILD WESTWARD. AS THE SUBTROPICAL STEERING RIDGE
(STR) AMPLIFIES WESTWARD, TS 11W WILL CONTINUE ITS NORTHWARD TRACK
INTO TAU 48. LEADING UP TO TAU 36 TO TAU 48, AN ADDITIONAL STR WILL
BUILD IN CLOSE VICINITY TO HONSHU, DRIVING THE SYSTEM NORTHWESTWARD
INTO TAU 96. AFTER TAU 96, TS 11W WILL CROSS THE STR AXIS AND BEGIN
ITS TRACK NORTH-NORTHEASTWARD, TOWARD WAKAYAMA, JAPAN BEFORE MAKING
LANDFALL JUST BEFORE TAU 120. IN REGARD TO INTENSITY, TS 11W IS
EXPECTED TO STEADILY INTENSIFY AS LOW TO MODERATE VWS (15-25 KTS)
WILL REMAIN PREVALENT DURING THE GENERALLY NORTHWARD TRACK INTO TAU
72, WHILE UPPER-LEVEL OUTFLOW REMAINS CONDUCIVE FOR FURTHER
DEVELOPMENT. AT THIS TIME, AN UPPER-LEVEL AREA OF CYCLONIC ROTATION
(TUTT CELL) WILL LIMIT THE SYSTEM'S EXHAUST MECHANISM UNTIL TS 11W
TRACKS NORTH OF THE STR AXIS. AFTER TAU 72, THE ENVIRONMENT WILL
SUPPORT FURTHER INTENSIFICATION WITH WARM SEA SURFACE TEMPERATURES,
LOW VWS, AND CONDUCIVE UPPER-LEVEL OUTFLOW, WITH TS 11W INTENSITIES
OF 105 KTS AT TAU 96 AND JUST BEFORE LANDFALL NEAR WAKAYAMA, JAPAN.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN MODERATE AGREEMENT
THAT TS 11W WILL TRACK GENERALLY NORTHWARD OVER THE NEXT 72 HOURS,
WITH THE EXCEPTION OF GFS, WHICH BRINGS THE SYSTEM FURTHER EAST
DURING THE INITIAL 72 HOURS OF THE FORECAST PERIOD. THE CROSS-TRACK
SPREAD AT TAU 72 IS 115 NM, AND THEN GRADUALLY INCREASES TO 170 NM
BY TAU 96, NEAR THE BEGINNING OF THE FORECASTED NORTHEASTWARD TRACK
OF THE SYSTEM. THE GFS (GEFS) AND ECMWF (EPS) ENSEMBLES SUPPORT THE
TRACK PHILOSOPHY, WITH THE LARGE MAJORITY OF SOLUTIONS INDICATING
THE RECURVE NORTH-NORTHEASTWARD AFTER TAU 96. THE JTWC TRACK IS
PLACED CLOSE TO CONSENSUS WITH MEDIUM CONFIDENCE. INTENSITY
GUIDANCE IS IN LOW AGREEMENT, WITH MODELS VARYING ON INTENSITY
GUIDANCE AFTER TAU 72 AND DURING THE BEGINNING OF THE NORTHEASTWARD
TRACK. OVERALL, THE JTWC INTENSITY FORECAST REMAINS CLOSE WITH THE
CONSENSUS DURING THE FIRST 72 HOURS OF THE FORECAST PERIOD, WHILE
INCREASING BETWEEN TAU 96 AND TAU 120 AS TS 11W APPROACHES MAINLAND
JAPAN. 

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