WDPN32 PGTW 220300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (SHANSHAN) WARNING 
NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.1N 141.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 263 NM WEST-NORTHWEST OF TINIAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS
CONSOLIDATION OF A WELL DEFINED SYMMETRIC CONVECTIVE CORE, WITH
INCREASINGLY TIGHT WRAPPING OF THE DEVELOPING BANDING FEATURES. THE
INITIAL POSITION WAS ADJUSTED APPROXIMATELY 50NM SOUTHWEST OF THE
PRIOR 6 HOUR INTERPOLATED FORECAST POSITION AFTER A LATE-ARRIVING
220029Z ASCAT-B PASS PROVIDED MUCH NEEDED CLARITY ON THE LOCATION
OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THE PREVIOUS BEST TRACK
WAS ADJUSTED TO ACCOUNT FOR THE WESTWARD SHIFT IN POSITIONING. THE
INITIAL INTENSITY WAS ASSESSED AT 40 KNOTS, BASED ON THE
AFOREMENTIONED ASCAT DATA, AND SUPPORTED BY ADT AND DPRINT
ESTIMATES, WHILE THE SUBJECTIVE DVORAK ESTIMATES CAME IN AT 35
KNOTS. THE ENVIRONMENT IS GENERALLY FAVORABLE WITH LOW (10-15 KNOT
VERTICAL WIND SHEAR) AND VERY WARM SST, THOUGH OUTFLOW IS ONLY 
MODERATE
AT THE MOMENT. TS SHANSHAN IS MORE ORGANIZED THAN CURRENT MODEL
ANALYSES GIVE IT CREDIT FOR. 

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WEAK STEERING FLOW IS BEING PROVIDED
BY MID-LEVEL RIDGING TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   RCTP: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   CIMSS SATCON: 31 KTS AT 211540Z
   CIMSS ADT: 41 KTS AT 220200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: INITIAL POSITION WAS ADJUSTED
APPROXIMATELY 50 NM SOUTHWEST OF THE PRIOR 6-HOUR INTERPOLATED
POSITION. THE NEW FORECAST TRACK WAS SHIFTED WEST OF THE PRIOR TRACK. 

FORECAST DISCUSSION: TS SHANSHAN IS EXPECTED TO TURN ON TO A
NORTHWARD TRACK OVER THE NEXT 24 HOURS AS A STEERING RIDGE (STR)
BUILDS TO THE EAST, HOWEVER, THE CURRENT WEAK STEERING FLOW AND 
TIMING OF THE TURN ADD UNCERTAINTY TO THE INITIAL TRACK MOTION. AFTER 
TAU 72, A NORTHWESTWARD DEFLECTION IS EXPECTED AS THE STR BUILDS IN 
AHEAD OF THE TRACK. INTENSITY GUIDANCE SPREAD IS EXTREMELY LARGE, 
BOTH IN THE INITIAL AND EXTENDED PERIODS. STATISTICAL GUIDANCE 
CONTINUES TO INTENSIFY THE SYSTEM OVER THE NEXT 36 HOURS, AS OUTFLOW 
GRADUALLY IMPROVES. HOWEVER, BETWEEN TAU 36 TO 48 THE INTENSIFICATION 
TREND IS SLOWED AS A DEVELOPING TUTT CELL TO THE WEST INCREASES THE 
VERTICAL WIND SHEAR OVER THE SYSTEM. BEYOND TAU 72, THE GFS CALLS FOR 
TUTT CELL TO MOVE INTO A MORE FAVORABLE POSITION, RESULTING IN 
RENEWED
INTENSIFICATION, WHEREAS THE ECMWF MAINTAINS A NEGATIVE
SUPERPOSITION OF THE TUTT FEATURE RESULTING IN WEAKENING OF THE 
SYSTEM. THE FORECAST IS HEDGED TOWARDS THE GFS SOLUTION GIVEN
THE OTHERWISE VERY FAVORABLE ENVIRONMENT IN THE LATER TAUS. GIVEN
THE UNCERTAINTIES DESCRIBED, THERE IS LOW CONFIDENCE IN THE TRACK
AND INTENSITY FORECAST AT THIS TIME. 

MODEL DISCUSSION: INITIAL MULTI-MODEL SPREAD IS HIGH, BUT COMES
INTO INCREASING AGREEMENT BY TAU 48 WITH A STRAIGHT-RUNNING TRACK
TOWARDS JAPAN. LIKEWISE, ENSEMBLE MODEL MEMBERS OVERWHELMING
INDICATE A RECURVATURE IS NOT LIKELY DURING THE FORECAST PERIOD. AS
NOTED, THERE IS SIGNIFICANT DISAGREEMENT ON INTENSITY, WHICH WILL
BE STRONGLY DEPENDENT ON WHEN TS 11W MAKES ITS NORTHWARD TURN AND
THE SUBSEQUENT LONGITUDINAL POSITIONING RELATIVE TO THE TUTT LATER
IN THE FORECAST. 

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