WDPN32 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 22.5N 140.7E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 142 NM SOUTH-SOUTHWEST OF IWO TO, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A
MEDIUM-SIZED SYSTEM THAT HAS MAINTAINED ITS TYPHOON INTENSITY WITH
DEEP CONVECTIVE TOP TEMPERATURES OVER THE COLD DENSE OVERCAST (CDO)
CYCLING UP AND DOWN AND OBSCURING THE LOW LEVEL CIRCULATION (LLC).
A ROBUST POLEWARD OUTFLOW AND DRY AIR INTRUSION ALONG THE WESTERN
FLANK ARE ALSO EVIDENT ON THE EIR LOOP. THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON THE WARMEST PIXELS IN THE
CENTER OF THE CDO, ADJUSTED FOR FORWARD TILT AND EXTRAPOLATED FROM
A DEFINED BEST-TRACK MID-POINT LLC FEATURE IN THE 240904Z SSMIS
37GHZ IMAGE. THE INITIAL INTENSITY OF 65KTS IS ALSO ASSESSED WITH
HIGH CONFIDENCE BASED ON THE MAJORITY 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
   KNES: T4.0 - 65 KTS
   CIMSS SATCON: 52 KTS AT 240951Z
   CIMSS ADT: 55 KTS AT 241130Z
   CIMSS AIDT: 64 KTS AT 241240Z
   CIMSS DPRINT: 64 KTS AT 241130Z

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
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,
MAKE LANDFALL JUST SOUTHWEST OF KYOTO, TRACK ACROSS HONSHU, THEN
EXIT INTO THE SEA OF JAPAN (SOJ) AROUND TAU 96. BY TAU 120, IT WILL
REACH THE SOUTHERN TIP OF THE RUSSIAN ISLAND OF SAKHALIN. 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 45KTS BY TAU 120.
CONCURRENTLY BY TAU 96, TY 11W WILL BEGIN EXTRA-TROPICAL TRANSITION
(ETT) AS IT ENTERS THE BAROCLINIC ZONE AND BECOME A STRONG
GALE-FORCE COLD CORE LOW WITH AN EXPANDING WIND FIELD BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN TIGHT AGREEMENT WITH A
GRADUAL AND EVEN SPREAD TO 158NM BY TAU 72, LENDING HIGH CONFIDENCE
TO THIS PORTION OF THE JTWC TRACK FORECAST (MEDIUM CONFIDENCE TO
THE INTENSITY FORECAST). AFTERWARD, THE MODEL ENVELOPE SPREADS OUT
UNEVENLY TO 481NM BY TAU 120. THIS WIDE RANGE PLUS THE VARIABILITY
ASSOCIATED WITH LAND INTERACTION AND ETT LEND LOW CONFIDENCE TO THE
EXTENDED PORTION OF THE TRACK AND INTENSITY FORECASTS. 

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