WDPN31 PGTW 210900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 25.6N 122.5E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 62 NM EAST-NORTHEAST OF TAIPEI, TAIWAN
   MOVEMENT PAST 6 HOURS: WESTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH FLARING CONVECTION
SHEARED TO THE SOUTHWEST. AN EARLIER 210145Z METOP-C ASCAT IMAGE
REVEALS WIND SPEEDS BETWEEN 25-30KTS IN THE NORTHERN SEMI-CIRCLE OF
THE CIRCULATION. THE SMALL AND FRAIL TROPICAL DEPRESSION (TD) IS IN
A MARGINALLY FAVORABLE ENVIRONMENT WITH CONFLUENCE IN THE
UPPER-LEVELS, DRY AIR EASTWARD OF THE CENTER, AND MODERATE 10-15KT
VERTICAL WIND SHEAR. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED LLCC REVEALED ON ANIMATED
MSI. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED SCATTEROMETRY ACCOMPANY BY THE 
AGENCY AND OBJECTIVE FIXES LISTED BELOW.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: LOW-LEVEL NORTHEASTERLY FLOW

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.0 - 25 KTS
   CIMSS ADT: 25 KTS AT 210540Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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: TROPICAL DEPRESSION (TD) 17W WILL CURVE
SOUTHWESTWARD UNDER THE LOW-LEVEL STEERING INFLUENCE OF THE
ENHANCED NORTHEASTERLY FLOW IN THE TAIWAN STRAIT. QUICKLY FOLLOWING
LANDFALL AFTER TAU 24, TD 17W WILL DISSIPATE OVER LAND BY THE END
OF THE FORECAST PERIOD. THE SYSTEM WILL REMAIN INFLUENCED BY HIGH
SHEAR, WHICH WILL KEEP THE VORTEX SHALLOW AND MITIGATE SIGNIFICANT
INTENSIFICATION PRIOR TO LANDFALL. ADDITIONALLY, THE UPPER-LEVEL
ENVIRONMENT WILL REMAIN CONFUSED AND DIVERGENT AT TIMES, FORFEITING
ANY CHANCE OF FAVORABLE UPPER-LEVEL OUTFLOW. THE PEAK INTENSITY
WILL BE 30KTS UNTIL THE SYSTEM IS FORCED TO DISSIPATE DUE TO
TOPOGRAPHIC INTERACTION.

MODEL DISCUSSION: DETERMINISTIC MODEL BIFURCATES AFTER TAU 0,
LEADING TO A LARGE AMOUNT OF UNCERTAINTY IN THE TRACK FORECAST. THE
VARIABILITY IN THE JTWC MULTI-MODEL CONSENSUS TRACKERS MAY BE
RELATED TO THE FACT THAT UNINTERPOLATED GUIDANCE HARDLY DEVELOPS A
CIRCULATION AT ALL AND THE SMALL SIZE OF THE SYSTEM IS DIFFICULT TO
REPRESENT IN THE RESOLUTION OF GLOBAL-SCALE MODELS. THE INTENSITY
GUIDANCE ALSO FOLLOWS THE TREND OF THE TRACK GUIDANCE, KEEPING THE
SYSTEM WEAK AND UNLIKELY TO DEVELOP. HOWEVER, THE GUIDANCE IS
SPORADIC AND MAY NOT REPRESENT THE GENUINE INTENSITY WELL.

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