WDPN32 PGTW 300300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (SHANSHAN) WARNING NR 
035//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 33.8N 131.3E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 50 NM SOUTHWEST OF IWAKUNI, JAPAN
   MOVEMENT PAST 6 HOURS: EAST-NORTHEASTWARD AT 02 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS CLOUD
BANDING CIRCULATING CYCLONICALLY AROUND AN OBSCURED LOW-LEVEL
CIRCULATION CENTER (LLCC) IN THE WARM WATERS (27-28C) OF SUO-NADA,
JAPAN. RADAR IMAGERY ALSO SUPPORTS AN LLCC REVEALED BY LOW-LEVEL
CLOUD BANDING WRAPPING INTO THE CENTER. OUTFLOW DEPICTED ON WATER
VAPOR IMAGERY IS NOT AS STRONGLY FEEDING INTO THE UPPER-LEVEL JET
TO THE NORTH AND CONVECTION IS NOT AS DEEP. DRY AIR IS APPARENT AND
IMPINGING ON THE CIRCULATION FROM THE SOUTHWEST. THE INITIAL
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED
RADAR IMAGERY AND ANIMATED MSI. THE INITIAL INTENSITY OF 40 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE
FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: PINNED WITHIN A COL BETWEEN TWO
SUBTROPICAL RIDGES (STR) TO THE EAST AND WEST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T2.5 - 35 KTS
   CIMSS SATCON: 42 KTS AT 292323Z
   CIMSS ADT: 41 KTS AT 292330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 0-5 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE 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: TROPICAL STORM (TS) 11W WILL REMAIN TRAPPED
BETWEEN TWO RIDGES DRIFTING EASTWARD FOR THE FIRST 24 HOURS OF THE
FORECAST. AT TAU 24, AN UPPER-LEVEL TROUGH WILL GRADUALLY ERODE THE
STR TO THE EAST WHILE THE TROPICAL STORM REMAINS QUASI-STATIONARY
IN MOTION THROUGH TAU 48, RESULTING IN A NORTH-NORTHEASTWARD TRACK
TOWARDS THE SEA OF JAPAN THROUGH THE END OF THE FORECAST PERIOD.
DURING THE QUASI-STATIONARY PERIOD, THE TRACK MAY DEVIATE BETWEEN
TAUS ALLOWING FOR LOOPING AND POSSIBLE BACKTRACKING THAT IS NOT
REFLECTED ON THE FORECAST. THE IRREGULAR MOTION MAY CAUSE THE
SYSTEM TO COME OUT OVER WATER IN KII-SUIDO OR REMAIN OVER THE
MOUNTAINOUS TERRAIN OF SHIKOKU. THIS WILL LEAD TO UNCERTAINTY IN
THE INTENSITY FORECAST, WHICH IS FORECAST TO GRADUALLY WEAKEN TO
30KTS BY TAU 24 AND DISSIPATE BY TAU 72. IF THE SYSTEM PASSES OVER
WATER FOR LONGER THAN REFLECTED IN THE FORECAST, IT IS POSSIBLE
THAT THE CIRCULATION MAY PERSIST FOR LONGER THAN REFLECTED IN THE
WARNING, AND ALTERNATIVELY IF THE SYSTEM INTERACTS MORE WITH
TOPOGRAPHY, IT MAY LEAD TO DISSIPATION EARLIER THAN REFLECTED IN
THE FORECAST. 

MODEL DISCUSSION: THE DETERMINISTIC MODEL GUIDANCE IS IN GOOD
AGREEMENT THAT TS 11W WILL TRACK NEARLY DUE WEST FOR THE FIRST 24
HOURS OF THE FORECAST PERIOD. AFTER TAU 24, THE JTWC MULTI-MODEL
CONSENSUS PRESENTS A VARIETY OF SOLUTIONS TRACKING THE SYSTEM OUT
OVER WATER OR KEEPING THE SYSTEM ON THE COAST. WHETHER THE SYSTEM
WILL BE ON OR OFF LAND IS DIRECTLY RELATED TO WHETHER THE STORM
INTENSIFIES OR DISSIPATES EARLIER OR LATER THAN TAU 72. MOST OF THE
JTWC INTENSITY GUIDANCE MAINTAINS A 30-40 INTENSITY BEFORE COMING
OUT OVER COOLER WATERS WITHIN THE SEA OF JAPAN, WITH THE EXCEPTION
OF HWRF, WHICH PEAKS UP TO 50KTS BY TAU 48. 

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