WDPN31 PGTW 222100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN) 
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 29.5N 135.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 324 NM SOUTH-SOUTHEAST OF IWAKUNI, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC), WITH DEEP 
PERSISTENT CONVECTION DISPLACED TO THE NORTH. AN EARLIER 221624Z
AMSR2 89GHZ MICROWAVE IMAGE REVEALS SHALLOW BANDING WRAPPING INTO
A LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS
PLACED WITH HIGH CONFIDENCE BASED ON EIR IMAGERY AND THE AMSR2
MICROWAVE IMAGERY. THE INITIAL INTENSITY OF 30 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON A 221500Z SHIP OBSERVATION LOCATED AT
28.4N 136.4E, REPORTING UP TO 30 KTS. AS WELL AS A COMBINATION OF 
AGENCY DVORAK INTENSITY ESTIMATES, PGTW T2.0, RJTD T1.5. ENVIRONMENTAL 
CONDITIONS ARE MARGINALLY FAVORABLE WITH ROBUST POLEWARD OUTFLOW, WARM 
(28-29C) SEA SURFACE TEMPERATURES (SSTS), OFFSET BY MODERATE (10-15 
KTS) VERTICAL WIND SHEAR.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   RJTD: T1.5 - 25 KTS
   CIMSS SATCON: 38 KTS AT 221231Z
   CIMSS ADT: 33 KTS AT 221750Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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: BASED ON THE OVERALL MARGINALLY FAVORABLE
ENVIRONMENT, TD 17W WILL STRUGGLE TO INTENSIFY OVER THE NEXT 12
HOURS, AND WILL LIKELY MAINTAIN ITS CURRENT INTENSITY WITH A
POSSIBLE BRIEF PERIOD OF INTENSIFICATION PRIOR TO LANDFALL.
THEREFORE, THE JTWC FORECAST CALLS FOR 17W TO REACH A POTENTIAL
MAXIMUM INTENSITY OF 35 KNOTS BY TAU 12. BY TAU 24, AS THE SYSTEM
TURNS AND TRACK TO THE NORTHEAST AROUND THE SUBTROPICAL RIDGE AXIS,
17W IS FORECAST TO MAKE LANDFALL OVER MAINLAND HONSHU. ADDITIONALLY, 
AN APPROACHING UPPER-LEVEL TROUGH TO THE NORTHWEST OF THE SYSTEM WILL 
BEGIN TO INTERACT WITH 17W WHILE INCREASING VERTICAL WIND SHEAR (VWS). 
AFTER TAU 36, 17W WILL CONTINUE TO WEAKEN DUE TO LAND INTERACTION FROM 
THE RUGGED TERRAIN OF THE JAPANESE ALPS. THEREFORE, SIGNIFICANTLY 
IMPACTING THE SYSTEMS STRUCTURE, WITH DISSIPATING FORECAST BY TAU 48.    

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT WITH ONLY A 40NM SPREAD UP TO TAU 24. THEREAFTER, THE
MODEL GUIDANCE SPREADS ONCE THE SYSTEM MAKES LANDFALL, WITH INCREASES 
IN BOTH CROSS TRACK AND ALONG TRACK VARIABILITY. LIKELY DUE TO HOW 
MODELS ARE STRUGGLING TO RESOLVE THE WEAK STRUCTURE OF THE CIRCULATION 
INDUCED BY INCREASED VERTICAL WIND SHEAR AND TERRAIN INTERACTION. 
THEREFORE, THE JTWC OFFICIAL TRACK FORECAST IS PLACED WITH MEDIUM 
CONFIDENCE. THE JTWC INITIAL INTENSITY IS CLOSE TO THE MULTI-MODEL 
CONSENSUS WITH MEDIUM CONFIDENCE THROUGHOUT THE FORECAST PERIOD.


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