WDPN32 PGTW 242100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.9N 139.5E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 112 NM WEST-SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 18 KTS
   SIGNIFICANT WAVE HEIGHT: 24 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS
STRUGGLING DEEP CONVECTION OBSCURING A LOW-LEVEL CIRCULATION CENTER
THAT IS CLEARLY SHEARED HIGH 20-25KT FROM THE SOUTHWEST. THE
SOUTHWESTERLY VERTICAL WIND SHEAR (VWS) IS INDUCED BY A TROPICAL
UPPER TROPOSPHERIC (TUTT) CELL LOCATED NEARBY TO THE NORTHWEST. THE
TUTT CELL IS COUNTERBALANCING THE UNFAVORABLE SHEAR BY ENCOURAGING
VERY STRONG POLEWARD OUTFLOW ALOFT. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON A 241824Z F-18 SSMIS 91GHZ IMAGE
DEPICTING THE DEEP CONVECTION DISPLACED FROM A MICROWAVE EYE-LIKE
FEATURE AND LOW-LEVEL CLOUD BANDING EXPOSED BY THE DRY AIR WRAPPING
IN FROM THE SOUTHWEST. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE FIXES
LISTED BELOW ACCOMPANIED BY THE PRESENCE OF THE MICROWAVE EYE-LIKE
FEATURE.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: THE NORTHWESTERN PERIPHERY OF A RIDGE
TO THE WEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 60 KTS AT 241607Z
   CIMSS ADT: 49 KTS AT 241730Z

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TYPHOON (TY) 11W WILL TRACK NORTHWESTWARD
WHILE UNDER THE STEERING INFLUENCE OF A WEAKENING RIDGE TO THE
EAST. BETWEEN TAU 12-24, THE SYSTEM WILL COME UNDER THE STEERING
INFLUENCE OF A DIFFERENT RIDGE AND CONTINUE TO ROUND THE RIDGE
THROUGH THE END OF THE FORECAST PERIOD, TRACKING THE SYSTEM OVER
MAINLAND JAPAN BETWEEN TAU 72-96. THE SYSTEM IS FORECAST TO RESUME
INTENSIFICATION SLOWLY WITHIN THE NEXT 12 HOURS AS VWS DROPS TO
MODERATE SPEEDS (15-20KTS). VWS WILL CONTINUE TO DECREASE AS THE
TUTT CELL CONTINUES WEST ALLOWING FOR A MORE DRAMATIC
INTENSIFICATION RATE WHILE IN A FAVORABLE ENVIRONMENT OF LOW VWS,
WARM SSTS, AND STRONG UPPER-LEVEL DIVERGENCE. AFTER 72 HOURS, THE
SYSTEM WILL BEGIN TO INTERACT WITH AN UPPER-LEVEL TROUGH EXTENDING
OVER THE SEA OF JAPAN WHICH WILL INITIATE EXTRATROPICAL TRANSITION
(ETT). THE INCREASE OF VWS, INTERACTION WITH LAND, AND ETT WILL
CAUSE WEAKENING TO START AT TAU 72 THAT WILL CONTINUE TO THE END OF
THE FORECAST PERIOD WHEN THE SYSTEM BECOMES FULLY EXTRATROPICAL AT
TAU 120.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THAT THE SYSTEM WILL TRACK NORTHWESTWARD AS THE STEERING INFLUENCE
IS PICKED UP BY THE SUBTROPICAL RIDGE TO THE NORTH, BUT UNCERTAINTY
IN THE LATER FORECAST TRACK INCREASES DUE TO A WIDE CROSS-TRACK
SPREAD OF 560NM. THE LARGE SPREAD OF SOLUTIONS BETWEEN TAU 72-120
CAN BE ATTRIBUTED TO DIFFERENT INTERPRETATIONS OF HOW STRONGLY THE
SYSTEM IS STEERED BY THE SUBTROPICAL RIDGE. DIFFERENT TRACK
SOLUTIONS WILL ULTIMATELY IMPACT THE DIFFERENT SOLUTIONS OF THE
INTENSITY GUIDANCE, WHICH HAS A 70KT SPREAD AT THE PEAK INTENSITY
BETWEEN TAU 48-72. GFS, WHICH HAS A MORE NORTH-NORTHEASTERLY TRACK
OVER WARMER WATERS, FORECASTS A PEAK OF 135KTS WHILE COAMPS-TC
(NAVGEM-BASED) FORECASTS A STAGNATION OF 65KTS THROUGHOUT THE
FORECAST. 

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