WDPN32 PGTW 250900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 016//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.9N 137.8E
   INITIAL INTENSITY: 70 KTS
   GEOGRAPHIC REFERENCE: 201 NM WEST-NORTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A MEDIUM-
SIZED SYSTEM THAT HAS REGAINED MOMENTUM AND BEGAN TO RE-CONSOLIDATE 
AS EVIDENCED BY COOLING CONVECTIVE TOPS OVER THE COLD DENSE OVERCAST 
(CDO) THAT IS OBSCURING THE LOW LEVEL CIRCULATION (LLC). A ROBUST 
POLEWARD OUTFLOW, A TUTT CELL 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 A MICROWAVE LLC FEATURE IN THE 
250601Z SSMIS IMAGE SUITE. THE INITIAL INTENSITY OF 70KTS IS ALSO 
ASSESSED WITH HIGH CONFIDENCE BASED ON THE HIGH END OF AGENCY AND 
OBJECTIVE DVORAK ESTIMATES AND REFLECTS THE IMPROVED 6-HR EIR 
SIGNATURE. ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH WARM 
ALONG-TRACK SST AND A STRONG, EFFICIENT VENTILATION ALOFT OFFSET BY 
MODERATE RELATIVE VWS, SUBSIDENCE FROM THE TUTT CELL TO THE WEST, AND 
COLD DRY AIR
INTRUSION AT THE LOWER LEVELS.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO
THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   CIMSS SATCON: 64 KTS AT 250500Z
   CIMSS ADT: 74 KTS AT 250530Z
   CIMSS AIDT: 70 KTS AT 250530Z
   CIMSS DPRNT: 59 KTS AT 250500Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 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 BY TAU 72, MAKE 
LANDFALL OVER SHIKOKU AND ACCELERATE NORTHEASTWARD ON THE POLEWARD 
SIDE OF THE STR, TRACK ACROSS HONSHU, THEN EXIT INTO THE SEA OF JAPAN 
(SOJ) AROUND TAU 84. BY TAU 120, IT WILL MAKE LANDFALL OVER HOKKAIDO 
NEAR SAPPORO. THE FAVORABLE ENVIRONMENT WILL FUEL A GRADUAL 
INTENSIFICATION TO A PEAK OF 110KTS BY TAU 48 AS POLEWARD OUTFLOW, 
ENHANCED BY THE STRONG WESTERLIES, PEAKS. AFTERWARD, LAND INTERACTION 
AND COOLER SST IN THE SOJ WILL RAPIDLY ERODE THE SYSTEM DOWN TO 45KTS 
BY TAU 120. CONCURRENTLY BY TAU 72, TY 11W WILL BEGIN EXTRA-TROPICAL 
TRANSITION (ETT) AS IT ENTERS THE COLD 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 A MERE 55NM BY TAU 72, LENDING HIGH
CONFIDENCE TO THIS PORTION OF THE JTWC TRACK FORECAST AND MEDIUM
CONFIDENCE TO THE INTENSITY FORECAST. AFTERWARD, THE MODEL ENVELOPE
SPREADS OUT UNEVENLY TO 326NM 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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