WDPN32 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (SHANSHAN) WARNING 
NR 033//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 33.4N 131.2E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 70 NM SOUTHWEST OF IWAKUNI, JAPAN
   MOVEMENT PAST 6 HOURS: NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 0 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AND A COMPOSITE
RADAR LOOP SHOW CONTINUED RAPID EROSION AND UNRAVELING OF CONVECTIVE 
TOPS AND FEEDER BANDS AS THE SYSTEM TRACKS ACROSS KYUSHU. THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE DEFINED 
CIRCULATION ON THE RADAR LOOP AND TRIANGULATION FROM NUMEROUS SURFACE 
WIND OBSERVATIONS. THE INITIAL INTENSITY IS EXTRAPOLATED FROM THE 
SAME WIND OBSERVATIONS AND ACCOMPANYING SEA LEVEL PRESSURE REPORTS 
WITH MEDIUM CONFIDENCE AND SUPPORTED BY RJTD AND AUTOMATED DVORAK 
ESTIMATES. ANALYSIS INDICATES A HIGHLY UNFAVORABLE ENVIRONMENT DUE TO 
INTERACTION WITH THE RUGGED TERRAIN.

INITIAL WIND RADII BASIS: SURFACE WIND OBSERVATIONS.

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T3.5 - 55 KTS
   CIMSS DPRNT: 43 KTS AT 291230Z
   CIMSS DMNT: 45 KTS AT 290940Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY UNFAVORABLE
   VWS: 10-15 KTS
   SST: OVER LAND
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL STORM SHANSHAN WILL TRACK MORE
EASTWARD ALONG THE EDGE OF A SHALLOWER SOUTHWEST EXTENSION OF THE
STEERING STR TO THE EAST, AND MOSTLY OVER LAND AS IT DRAGS ACROSS
THE ISLANDS OF KYUSHU INTO SHIKOKU, AND HONSHU. BY TAU 48, A
SECONDARY STR TO THE WEST WILL COMPETE FOR STEERING AND PLACE THE
SYSTEM IN A QUASI-STATIONARY MODE. THE HIGHLY UNFAVORABLE
ENVIRONMENT WILL EVENTUALLY ERODE THE SYSTEM TO DISSIPATION BY TAU
72, POSSIBLY SOONER. HOWEVER, THERE IS ALSO A POSSIBILITY, AS
INDICATED BY A FEW NUMERICAL TRACK MODELS, THAT THE SYSTEM WILL
MAKE A TIGHT U-TURN BACK INTO THE PACIFIC OCEAN AND RE-INTENSIFY. 


MODEL DISCUSSION: THE NUMERICAL TRACK MODELS ARE IN GOOD AGREEMENT
UP TO TAU 36; AFTERWARD, NVGM, GFS, AND AEMN LOOP THE VORTEX
CLOCKWISE BACK OVER WATER. THE MAJORITY OF THE MODELS SLOW DOWN THE
VORTEX UP TO TAU 72 BEFORE ACCELERATING IT NORTHEASTWARD THROUGH
HONSHU. IN VIEW OF THESE, THERE IS ONLY MEDIUM CONFIDENCE IN THE
JTWC TRACK FORECAST. GIVEN THE VARIABILITY OF A LAND TRACK AND THE
POSSIBILITY OF A RETURN TO WATER, THERE IS LOW CONFIDENCE IN THE
JTWC INTENSITY FORECAST.  

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