WDPN32 PGTW 240900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.1N 141.1E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 222 NM SOUTH OF IWO TO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A
MEDIUM-SIZED SYSTEM THAT HAS OVERALL MAINTAINED ITS TYPHOON
INTENSITY WITH DEEP CONVECTIVE TOP TEMPERATURES OVER THE COLD DENSE
OVERCAST CYCLING UP AND DOWN. A ROBUST POLEWARD OUTFLOW AND DRY AIR
INTRUSION ALONG THE WESTERN FLANK ARE ALSO EVIDENT IN THE EIR LOOP.
THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A
DEFINED LOW LEVEL CIRCULATION FEATURE IN THE 240613Z SSMIS 37GHZ
IMAGE. THE INITIAL INTENSITY OF 65KTS IS ALSO ASSESSED WITH HIGH
CONFIDENCE BASED ON THE HIGH END OF AGENCY AND OBJECTIVE DVORAK
ESTIMATES AND REFLECTS THE SUSTAINED 6-HR EIR SIGNATURE. ANALYSIS
INDICATES AN OVERALL MARGINALLY FAVORABLE ENVIRONMENT WITH WARM
ALONG-TRACK SST AND STRONG VENTILATION ALOFT OFFSET BY MODERATE
RELATIVE VWS AND COLD DRY AIR INTRUSION AT THE LOWER LEVELS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   CIMSS SATCON: 59 KTS AT 240338Z
   CIMSS ADT: 55 KTS AT 240530Z
   CIMSS AIDT: 63 KTS AT 240530Z
   CIMSS DPRINT: 66 KTS AT 240700Z
   CIMSS MINT: 66 KTS AT 240338Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 SHANSHAN WILL CONTINUE ON A MORE
NORTHWESTWARD TRACK AS THE STEERING STR BUILDS. AFTER TAU 48, IT
WILL TURN MORE NORTHWARD AS IT CRESTS THE STR AXIS AND AFTER TAU
72, WILL ACCELERATE NORTHEASTWARD ON THE POLEWARD SIDE OF THE STR, 
MAKING LANDFALL JUST SOUTH OF KYOTO, TRACK ACROSS HONSHU THEN EXIT 
INTO THE SEA OF JAPAN (SOJ) AROUND TAU 96. BY TAU 120, IT WILL REACH 
THE NORTHERN TIP OF HOKKAIDO. THE MARGINALLY FAVORABLE ENVIRONMENT 
WILL FUEL A GRADUAL INTENSIFICATION TO A PEAK OF 105KTS BY TAU 72 AS 
POLEWARD OUTFLOW CONTINUES TO INCREASE. AFTER TAU 72, LAND 
INTERACTION AND COOL SST IN THE SOJ WILL RAPIDLY ERODE THE SYSTEM 
DOWN TO 35KTS BY TAU 120. CONCURRENTLY BY TAU 96, TY 11W WILL BEGIN 
EXTRA-TROPICAL TRANSITION (ETT) AS IT ENTERS THE BAROCLINIC ZONE, 
BECOMING A GALE-FORCE COLD CORE LOW WITH AND EXPANDING WIND FIELD BY 
TAU 120.    

MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT WITH A
GRADUAL AND EVEN SPREAD TO 190NM BY TAU 72 THEN TO 287NM BY TAU
120, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST (MEDIUM
CONFIDENCE TO THE INTENSITY FORECAST) UP TO TAU 72 ONLY. AFTERWARD,
THE VARIABILITY ASSOCIATED WITH LAND INTERACTION AND ETT LENDS LOW
CONFIDENCE TO THE EXTENDED PORTION OF THE TRACK AND INTENSITY
FORECASTS. 

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