WDPN31 PGTW 221500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 28.5N 136.1E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 334 NM WEST-NORTHWEST OF CHICHI JIMA
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 16 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS DEEP
PERSISTENT CONVECTION TO THE NORTH OF AN EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC). ENVIRONMENTAL CONDITIONS ARE MARGINALLY
FAVORABLE WITH ROBUST POLEWARD OUTFLOW, WARM (28-29C) SST VALUES,
BEING OFFSET BY MODERATE VERTICAL WIND SHEAR. THE INITIAL POSITION
IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE EIR IMAGERY AND
EXTRAPOLATION OF A 220853Z SSMIS 91GHZ IMAGE. THE INITIAL INTENSITY
OF 30KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE MULTIPLE
AGENCY DVORAK INTENSITY ESTIMATES AT T1.5-T2.0 AND THE OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE
NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS SATCON: 44 KTS AT 220854Z
   CIMSS ADT: 32 KTS AT 221150Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: ENVIRONMENTAL CONDITIONS REMAIN MARGINALLY
FAVORABLE AS CHARACTERIZED BY WARM SEA SURFACE TEMPERATURES (SSTS)
(28-29C) AND STRONG POLEWARD OUTFLOW INDUCED BY AN UPPER-LEVEL JET,
WHICH REMAINS LAID ACROSS THE SEA OF JAPAN. TD 17W WILL TRACK ALONG
THE WESTERN PERIPHERY OF A DEEP-LAYER SUBTROPICAL RIDGE (STR). TD
17W WILL BEGIN ROUNDING THE RIDGE AXIS BETWEEN TAUS 12 AND 24 AND
INCREASE IN TRACK SPEED AND ONLY INCREASE INTENSITY TO A PEAK OF
35KTS AS AN APPROACHING UPPER-LEVEL TROUGH MOVES IN FROM THE WEST,
WHILE VERTICAL WIND SHEAR INCREASES OVER MAINLAND HONSHU. TD 17W IS
EXPECTED TO MAKE LANDFALL NEAR THE CITY OF TAHARA, AICHI
PREFECTURE, JAPAN BETWEEN TAU 24 AND 36. TD 17W WILL CONTINUE ON A
NORTHEAST TRACK ENCOUNTERING THE RUGGED TERRAIN OF THE JAPANESE
ALPS, WHEREBY BEGINNING THE DISSIPATION PROCESS, COMPLETELY
DISSIPATING BY TAU 72 OVER WATER.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT WITH ONLY A 36NM SPREAD UP TO TAU 24. THEREAFTER, THE
MODEL GUIDANCE ONLY WIDENS TO 98NM ONCE THE SYSTEM MAKES LANDFALL,
EXCLUDING JGSM, WHICH NEVER INDICATES LANDFALL FOR THE SYSTEM. THE
OVERALL JTWC TRACK GUIDANCE CONFIDENCE IS HIGH FOR THE FIRST 24
HOURS, AND LOW THEREAFTER, AS THE CIRCULATION WEAKENS RAPIDLY
OVERLAND DUE TO SHEAR AND TERRAIN INTERACTION. THEREFORE, THE JTWC
OFFICIAL TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE. THE JTWC
INITIAL INTENSITY CONFIDENCE IS MEDIUM UP TO TAU 24 BUT DECREASES
TO LOW ONCE LANDFALL OCCURS DUE TO THE LAND INTERACTION.

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