WDPN32 PGTW 310300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 11W (SHANSHAN)
WARNING NR 039//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
SUMMARY:
INITIAL POSITION: 33.6N 135.5E
INITIAL INTENSITY: 30 KTS
GEOGRAPHIC REFERENCE: 174 NM EAST-SOUTHEAST OF IWAKUNI, JAPAN
MOVEMENT PAST 6 HOURS: EASTWARD AT 12 KTS
SIGNIFICANT WAVE HEIGHT: OVER LAND
SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
DEPRESSION 11W (SHANSHAN) QUICKLY TRACKING EASTWARD WITH AN ERODED
AND DISORGANIZED LOW-LEVEL CIRCULATION CENTER (LLCC). CONVECTION
HAS SLIGHTLY INCREASED OVER THE PAST 6 HOURS AS MORE OF THE
CIRCULATION MOVES BACK OVER WATER. ENVIRONMENTAL ANALYSIS INDICATES
THAT 11W IS IN AN UNFAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG
POLEWARD OUTFLOW AND RELATIVELY WEAK VERTICAL WIND SHEAR GREATLY
OFFSET BY INTERACTION WITH THE RUGGED TERRAIN OF JAPAN. THE INITIAL
POSITION IS PLACED WITH LOW CONFIDENCE BASED ON THE DISORGANIZED
LLCC SEEN IN THE ANIMATED MSI. THE INITIAL INTENSITY OF 30 KTS IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE OBJECTIVE AND
SUBJECTIVE INTENSITY ESTIMATES LISTED BELOW.
INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).
CURRENT STEERING MECHANISM: SHALLOW LAYER OF SOUTHWEST EXTENSION OF
THE SUBTROPICAL RIDGE (STR) TO THE EAST.
AGENCY DVORAK AND AUTOMATED FIXES:
PGTW: NO CURRENT ESTIMATE
RJTD: T2.0 - 30 KTS
CIMSS ADT: 31 KTS AT 310000Z
CIMSS DPRINT: 31 KTS AT 310000Z
CIMSS DMINT: 28 KTS AT 302150Z
FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
VWS: 5-10 KTS
SST: OVER LAND
OUTFLOW: STRONG POLEWARD
ANALYSIS CONFIDENCE:
INITIAL POSITION: LOW
INITIAL INTENSITY: MEDIUM
INITIAL WIND RADII: NOT APPLICABLE
3. FORECAST REASONING.
SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.
FORECAST DISCUSSION: 11W IS FORECAST TO TRACK EAST-SOUTHEASTWARD
OVER THE NEXT 12 HOURS. AFTERWARD, A SECONDARY STR TO THE WEST WILL
COMPETE FOR STEERING AND WILL CAUSE THE SYSTEM TO BECOME NEARLY
QUASI-STATIONARY THROUGH TAU 24 WITH A VERY SLOW DRIFT NORTHWARD.
AFTER TAU 24, STEERING BECOMES MORE DEFINED IN THE NORTH-SOUTH
ORIENTATION AND 11W IS THEN FORECAST TO TRACK NORTHWARD. BETWEEN
TAU 24 AND 36 A FINAL LANDFALL SOUTHEAST OF KYOTO IS ANTICIPATED.
REGARDING INTENSITY, THE 30 KNOT INTENSITY IS EXPECTED TO HOLD FOR
THE NEXT 12 HOURS AS THE CIRCULATION MAKES ITS WAY OFFSHORE. AFTER
MAKING LANDFALL THE SYSTEM IS EXPECTED TO QUICKLY DISSIPATE DUE TO
TERRAIN INTERACTION.
MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN POOR AGREEMENT
REGARDING BOTH TRACK AND INTENSITY AFTER TAU 12. THE COMPETING
STEERING ENVIRONMENT CAUSES VORTEX TRACKERS TO BECOME ERRATIC. THE
HIGH VARIANCE IN TIMING AND SHARPNESS OF THE NORTHWARD TURN LENDS
LOW CONFIDENCE IN THE JTWC TRACK FORECAST. THE INTENSITY GUIDANCE
FOLLOWS SUIT, THE VARIANCE IN TIME OVER WATER CAUSES A DISAGREEMENT
IN INTENSITY. THE LONGER THE VORTEX REMAINS OVER WATER, THE LONGER
THE WINDOW THERE IS FOR REINTENSIFICATION (WHICH GFS AND HWRF BOTH
HINT AT). AS A RESULT, THE JTWC INTENSITY FORECAST IS ALSO PLACED
WITH LOW CONFIDENCE.
FORECAST CONFIDENCE:
TRACK 0 - 72 HR: LOW
INTENSITY 0 - 72 HR: LOW//
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