WDPN31 PGTW 131500
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: 6.3N 139.8E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 327 NM EAST OF KOROR
   MOVEMENT PAST 6 HOURS: SOUTHWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL DEPRESSION (TD) 17W (SEVENTEEN) HAS PULLED A FAST ONE, AND
EMERGED IN ANIMATED SHORTWAVE INFRARED (SWIR) AND PROXY VISIBLE
(PROXYVIS) AS NOW BEING A FULL EXPOSED LOW LEVEL CIRCULATION CENTER
(LLCC) MOVING SOUTH-SOUTHEASTWARD. THIS MOTION IS CONFIRMED BY A
131229Z ASCAT-C BULLSEYE PASS, RESULTING IN A SECOND RELOCATION IN
THE LAST 12 HOURS. THE INITIAL POSITION IS PLACED IN THE WESTERN
END OF AN AREA OF ELONGATED ROTATION AS EVIDENCED IN THE
SCATTEROMETER PASS. MULTIPLE VORTICES ARE CLEARLY EVIDENT IN THE
ANIMATED SWIR AND PROXYVIS AND THE INITIAL POSITION IS PLACED IN
THE CENTROID OF THESE SMALL CIRCULATIONS WITH HIGH CONFIDENCE. THE
INITIAL INTENSITY IS ASSESSED AT A GENEROUS 25 KNOTS, IN LIGHT OF A
THE SCATTEROMETER DATA WHICH SHOWS A PATCH OF 25-27 KNOT WINDS
CONFINED TO THE NORTHWEST SECTOR OF THE CIRCULATION. THE SYSTEM
CLEARLY HAS LOST ITS BATTLE WITH THE PERSISTENT EASTERLY SHEAR,
WHICH PROVED JUST TOO MUCH TO OVERCOME. NOW BEING AN EXPOSED LLCC
CONFINED TO THE LOW LEVELS, THE SYSTEM HAS TURNED SOUTHWARD, LIKELY
INFLUENCED AT THE MESOSCALE LEVEL BY THE ENHANCED POCKET OF WINDS
TO THE NORTHWEST, AS THE OVERALL ENVIRONMENTAL STEERING FLOW SHOULD
BE TO THE SOUTHWEST.

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

CURRENT STEERING MECHANISM: MESOSCALE EFFECTS IN RESPONSE TO
ENHANCED FLOW TO THE NORTHWEST, OTHERWISE UNDER THE INFLUENCE OF
THE LOW-LEVEL NORTHEASTERLY FLOW ON THE SOUTH SIDE OF A SUBTROPICAL
RIDGE (STR) TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: NO CURRENT ESTIMATE
   RJTD: T1.5 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 33 KTS AT 131130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THE INITIAL POSITION HAS BEEN SHIFTED
OVER 100NM FURTHER TO THE SOUTHEAST THAN WHERE THE POSITION WAS
FORECASTED TO BE. 

FORECAST DISCUSSION: IN THE NEAR-TERM, TD 17W IS LIKELY TO CONTINUE
TO WEAKEN BELOW WARNING CRITERIA AS IT REMAINS QUASI-STATIONARY AND
DRIFTING IN A LOOPING MANNER. NO SIGNIFICANT CHANGE IS EXPECTED IN
THE STRENGTH OF THE EASTERLY SHEAR, AND WHILE SPORADIC CONVECTION
IS LIKELY TO FLARE ALONG LOCALIZED CONVERGENT FLOW LINES, IT IS
UNLIKELY TO BE ABLE TO CONSOLIDATE INTO A COHERENT CORE. BUT WHILE
THE SYSTEM IS FORECAST TO WEAKEN BELOW WARNING CRITERIA, IT IS ALSO
EXPECTED TO REGENERATE LIKE A PHOENIX AFTER TAU 36. BY TAU 36 THE
STEERING GRADIENT IS EXPECTED TO STRENGTHEN, AND TD 17W WILL KICK
OUT TO THE WEST, ACCELERATING PAST PALAU BY TAU 60 BEFORE SLOWING
AND TURNING MORE POLEWARD BY THE END OF THE FORECAST PERIOD. MODEL
FIELDS SUGGESTS A WEAKENING OF THE DEEP-LAYER SHEAR AFTER TAU 36,
WHICH SHOULD ALLOW THEY SYSTEM TO MAKE ANOTHER RUN AT
INTENSIFICATION, ALBEIT SLOWLY AND WEAKLY. BY TAU 36 THE SYSTEM IS
FORECAST TO REGAIN 25 KNOTS, THEN SLOWLY INCREASE TO 35 KNOTS BY
THE END OF THE FORECAST PERIOD, AS IT APPROACHES THE EASTERN
PORTION OF THE PHILIPPINES. HOWEVER, IF CONVECTION FAILS TO DEVELOP
OR THE SYSTEM REMAINS STALLED NEAR ITS CURRENT POSITION, THEN THE
SYSTEM WILL FAIL TO REINTENSIFY AND DISSIPATE WITHIN THE NEXT 36
HOURS. 

MODEL DISCUSSION: IN LIGHT OF THE RECENT RELOCATION AND SIGNIFICANT
CHANGE IN THE OVERALL STRUCTURE OF THE STORM, THE FORECAST CAN BE
SUMMED UP AS ONE OF EXTREMELY LOW CONFIDENCE, IN BOTH TRACK AND
INTENSITY. TRACK GUIDANCE IS SCATTERED ACROSS A VERY WIDE SWATH IN
BOTH THE ALONG- AND CROSS-TRACK DIMENSIONS, PRIMARILY IN RESPONSE
TO THE MAJOR SHIFTS IN THE INITIAL POSITION. OF NOTE, THE BULK OF
THE TRACKERS SHOW ONLY A SMALL AMOUNT ADDITIONAL SOUTHWARD MOTION
BEFORE TURNING BACK TO THE WEST. ALL MODELS ARE CONSISTENT WITH A
WEST-NORTHWEST TRACK EXCEPT FOR THE GFS WHICH PERSISTS IN TRACKING
THE SYSTEM DUE WEST AND INTO THE SOUTH CHINA SEA. INTENSITY
GUIDANCE IS FOR THE MOST PART IN GOOD AGREEMENT THAT THE SYSTEM
WILL EITHER WEAKEN SLIGHTLY OR REMAIN STAGNANT FOR THE NEXT 36
HOURS. THEN THE MESOSCALE MODELS SHOW SLOW INTENSIFICATION THROUGH
TAU 96, INCREASING MORE SHARPLY BY THE END OF THE FORECAST.
MEANWHILE THE SHIPS (BOTH VERSIONS) GUIDANCE HOLDS THE SYSTEM
STEADY TO TAU 36, THEN WEAKENS IT TO 20 KNOTS THEN SHARPLY
INCREASES IT AFTER TAU 96 TO 45 KNOTS. COAMPS-TC REMAINS A TRUE
BELIEVER, RAPIDLY INTENSIFYING THE SYSTEM TO 75 KNOTS BY TAU 120,
WHICH GIVEN THE CURRENT STATE OF THINGS, SEEMS HIGHLY UNLIKELY. THE
JTWC FORECAST IS A BLEND OF THE GUIDANCE, GENERALLY BELOW THE
CONSENSUS MEAN, WITH VERY LOW CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: LOW
   TRACK 72-120 HR: LOW
   INTENSITY 0 - 72 HR: LOW
   INTENSITY 72-120 HR: LOW//
NNNN