WDPN32 PGTW 240300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.0N 141.3E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 288 NM SOUTH OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 17 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS DEEP LAYER
CONVECTION WRAPPING IN TO A LOW-LEVEL CIRCULATION CENTER (LLCC)
WITH DRY AIR ENTRAINING INTO THE CENTER FROM THE SOUTHWEST OF THE
SYSTEM. A TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT) CELL TO THE
WEST-NORTHWEST HAS BEGUN TO ENHANCE STRONG OUTFLOW POLEWARD ON
WATER VAPOR IMAGERY.  THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON A 232344Z METOP-B ASCAT WIND AMBIGUITIES IMAGE
REVEALING A DISTINCT CIRCULATION CENTER AND WAS ALSO BASED ON THE
AFOREMENTIONED ANIMATED MSI. THE INITIAL INTENSITY OF 65 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE
FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: ON THE WESTERN PERIPHERY OF A RIDGE TO
THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   CIMSS ADT: 53 KTS AT 232330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON 11W IS FORECAST TO TRACK NORTH OVER
THE NEXT 12 HOURS BEFORE TRACKING NORTHWESTWARD UNDER THE STEERING
INFLUENCE OF A SUBTROPICAL RIDGE TO THE NORTHEAST. THE SYSTEM WILL
ROUND THE RIDGE BEFORE ULTIMATELY TRACKING NORTHEASTWARD BY THE END
OF THE FORECAST PERIOD. THE SYSTEM WILL CONTINUE TO BE HEAVILY
SHEARED BY THE CLOSE PROXIMITY OF THE TUTT CELL LOCATED TO THE
WEST. AS THE TUTT DRIFTS WEST, SHEAR WILL SIGNIFICANTLY DECREASE
BETWEEN TAU 36-60. THE ENVIRONMENT WILL REMAIN HIGHLY FAVORABLE
WITH LOW SHEAR, STRONG UPPER-LEVEL DIVERGENCE, AND WARM SEA SURFACE
TEMPERATURES UNTIL THE SYSTEM MAKES LANDFALL AND INTERACTS WITH THE
TOPOGRAPHY OF JAPAN. JUST BEFORE TAU 96 THE SYSTEM BEGINS
EXTRATROPICAL TRANSITION AS IT INTERACTS AND EMBEDS INTO AN
UPPER-LEVEL JET AND COMPLETES TRANSITION BY TAU 120. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
FOR THE FIRST 48 HOURS OF THE TRACK WITH A MAXIMUM CROSS-TRACK
SPREAD OF 120NM. THE MODEL SPREAD OPENS BASED ON VARIED
INTERPRETATIONS OF HOW STRONGLY THE SYSTEM INTERACTS WITH THE STR
TO THE NORTHEAST, OPENING THE CROSS-TRACK SPREAD TO 220NM BY THE
END OF THE FORECAST. THE JTWC INTENSITY GUIDANCE SPREADS
SIGNIFICANTLY BY TAU 36 AS SHEAR LESSENS AND THE ENVIRONMENT IS
MORE FAVORABLE. HAFS-A SHOWS A PEAK OF 125KTS WHILE GFS IS THE
LOWEST AND REPRESENTS A PEAK OF 90KTS. THE SPREAD CAN BE ATTRIBUTED
TO VARIATIONS OF HOW FAVORABLE THE ENVIRONMENT IS AND THE DIFFERENT
TRACK SOLUTIONS, SOME OF WHICH CARRY THE TYPHOON OVER WATER FOR LONGER
THAN OTHERS. 

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