WDPN31 PGTW 021500
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: 27.5N 158.9E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 1169 NM SOUTHEAST OF MISAWA, JAPAN
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER WITH FLARING DEEP 
CONVECTION DISPLACED TO THE SOUTHWEST. THE INITIAL POSITION IS BASED 
ON A 020932Z ASCAT-A IMAGE SHOWING A CLEARLY DEFINED CIRCULATION OF 
25 KT WINDS WITH A SWATH OF 30 KT WINDS IN THE SOUTHEAST QUADRANT. 
THE INITIAL INTENSITY OF 30 KTS IS BASED ON MULTIPLE AGENCY DVORAK
ESTIMATES AND THE PREVIOUSLY MENTIONED ASCAT-A IMAGE.

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

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE LOCATED TO THE
EAST-NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 35 KTS AT 021140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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: TD 17W IS CURRENTLY TRACKING NORTHWESTWARD
UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE (STR) LOCATED TO THE
EAST-NORTHEAST. BY TAU 12, THE SYSTEM WILL INTENSIFY SLIGHTLY TO 35
KTS AND TURN NORTHWARD AS IT BEGINS TO ROUND THE STR AXIS.
AFTERWARDS, DECREASING SEA SURFACE TEMPERATURES WILL BEGIN TO
GRADUALLY WEAKEN THE SYSTEM. BY TAU 36, TD 17W WILL BEGIN TO
ACCELERATE NORTHEASTWARD AS IT BEGINS INTERACTING WITH THE
WESTERLIES IN THE BAROCLINIC ZONE. AROUND TAU 48, THE SYSTEM WILL 
BEGIN TO EXPERIENCE RAPIDLY INCREASING VERTICAL WIND SHEAR (VWS), 
WHICH IN ADDITION TO FURTHER COOLING SEA SURFACE TEMPERATURES, WILL 
BEGIN EXTRA-TROPICAL TRANSITION (ETT). TD 17W IS EXPECTED TO 
COMPLETE ETT NO LATER THAN TAU 72.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT IN REGARDS
TO FORECAST TRACK WITH THE EXCEPTION OF NVGM AND AFUM WHICH ARE
WESTERN OUTLIERS.  THEREFORE, THE JTWC FORECAST TRACK IS PLACED
SLIGHTLY TO THE RIGHT OF THE MODEL CONSENSUS. INTENSITY GUIDANCE IS
IN RELATIVELY FAIR AGREEMENT WITH ALL CONSENSUS MEMBERS KEEPING THE 
INTENSITY UNDER 35 KTS AND THEN WEAKENING THE SYSTEM FOR THE 
REMAINDER OF THE FORECAST PERIOD. THE JTWC INTENSITY FORECAST IS 
PLACED SLIGHTLY ABOVE INTENSITY CONSENSUS AT TAU 12 TO CONTINUE THE 
OBSERVED TREND OF STEADY INTENSIFICATION, AND THEN IS SLIGHTLY BELOW 
CONCENSUS AT LATER TAUS TO ACCOUNT FOR WEAKENING DUE TO 
EXTRATROPICAL TRANSITION.

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