WDPN32 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 11W (SHANSHAN) WARNING NR 009//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.2N 141.3E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 396 NM SOUTH OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 26 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TYPHOON
11W (SHANSHAN) WITH A VERY RAGGED EYE-LIKE FEATURE THAT STARTED
FORMING RIGHT AROUND 1200Z WITH VIGOROUS BURSTS OF CONVECTION IN
THE NORTHERN SEMICIRCLE. THE DRY AIR TO THE WEST AND SOUTHWESTERLY
SHEAR REMAIN ACTING ON THE SYSTEM, KEEPING THE WESTERN PERIPHERY
FREE OF CONVECTION. ENVIRONMENTAL ANALYSIS INDICATES THAT 11W IS
CURRENTLY IN A MARGINALLY FAVORABLE ENVIRONMENT FOR FURTHER
INTENSIFICATION CHARACTERIZED BY MODERATE POLEWARD AND EQUATORWARD
OUTFLOW ALOFT, MODERATE VERTICAL WIND SHEAR, AND WARM SEA SURFACE
TEMPERATURES. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON THE RAGGED EYE FEATURE SEEN IN THE ANIMATED EIR SATELLITE
IMAGERY. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED WITH MEDIUM
CONFIDENCE BASED ON THE AGENCY DVORAK ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: WESTERN PERIPHERY OF A SOUTHWARD
EXTENDING RIDGE TO THE EAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T3.5 - 55 KTS
   RCTP: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD
   OTHER FACTORS: DRY AIR TO THE WEST AND A TUTT CELL POSITIONED TO
THE NORTHWEST OF THE SYSTEM.

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: A QUICKER RATE OF INTENSIFICATION
AFTER TAU 36. 

FORECAST DISCUSSION: 11W IS FORECAST TO CONTINUE TRACKING NORTHWARD
ALONG THE WESTERN PERIPHERY OF THE RIDGING TO THE EAST THROUGH TAU
24. AFTER TAU 24, A SUBTROPICAL RIDGE IS EXPECTED TO BUILD EAST OF
HONSHU WHICH WILL TURN THE SYSTEM NORTHWESTWARD THROUGH TAU 72.
NEAR TAU 72, 11W IS FORECAST TO BEGIN ROUNDING THE STR AND TRACK
NORTHEASTWARD FOR THE REMAINDER OF THE FORECAST PERIOD WITH
LANDFALL OCCURRING IN JAPAN NEAR TAU 108. REGARDING INTENSITY, 11W
IS FORECAST TO STEADILY INTENSIFY TO 80 KTS AT TAU 36. THE RATE OF
INTENSIFICATION IS CAPPED BY THE PRESENCE OF THE TUTT CELL
CURRENTLY POSITIONED TO THE NORTHWEST, INCREASING VERTICAL WIND
SHEAR ON THE SYSTEM. AFTER TAU 36, THE TUTT CELL WILL MOVE INTO A
MORE FAVORABLE POSITION AND ALLOW 11W TO STRENGTHEN AS SHEAR
DRASTICALLY DROPS. AN INCREASE OF 40 KTS FROM TAU 36 (80 KTS) TO
TAU 72 (120 KTS) IS FORECASTED IN RESPONSE TO THE EXTREMELY
FAVORABLE ENVIRONMENTAL CONDITIONS. AS 11W BEGINS TO ROUND THE STR
A PEAK INTENSITY COULD OCCUR GREATER THAN 120 KTS (BETWEEN TAUS 72
AND 96). IN ANY CASE, 120 KTS IS FORECASTED AT TAU 96 BEFORE MAKING
LANDFALL. AFTER LANDFALL, TERRAIN INTERACTION WILL RAPIDLY WEAKEN
11W TO AROUND 60 KTS NEAR THE END OF THE FORECAST PERIOD.  

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN RELATIVELY GOOD
AGREEMENT WITH A 140 NM CROSS-TRACK SPREAD AT TAU 96. THE SOLE
OUTLIER BEING GALWEM, WHICH TRACKS THE SYSTEM MUCH FASTER THAN THE
OTHER MODELS. THE JTWC TRACK FORECAST IS PLACED SLIGHTLY SLOWER
THAN CONSENSUS FOR THE ENTIRETY OF THE TRACK TO OFFSET GALWEM.
INTENSITY GUIDANCE REMAINS IN WORSE AGREEMENT. THROUGH TAU 36,
MODELS AGREE ON THE GRADUAL INTENSIFICATION TO AROUND 80 KTS.
HOWEVER, AFTER TAU 36, MODELS DIVERGE WITH COAMPS-TC AND HAFS-A
SUGGESTING A RAPID RATE OF INTENSIFICATION THROUGH TAU 84. PEAK
INTENSITIES RANGE BETWEEN 125-145 KTS FOR THESE MODELS. ON THE
OTHER END OF THE SPECTRUM, GFS AND THE STATISTICAL DYNAMICAL MODELS
SUGGEST A PEAK OF AROUND 95 KTS. THE JTWC INTENSITY FORECAST IS
PLACED CLOSED TO CONSENSUS THROUGH TAU 36 AND MORE IN LINE WITH THE
FORMER GROUPING AS ENVIRONMENTAL CONDITIONS WILL BE HIGHLY
CONDUCIVE FOR 11W. THE HIGH VARIANCE IN GUIDANCE LENDS OVERALL LOW
CONFIDENCE IN THE JTWC INTENSITY FORECAST.  

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