WDPN31 PGTW 201500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 25W (TWENTYFIVE) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.7N 127.4E
   INITIAL INTENSITY: 25 KTS
   GEOGRAPHIC REFERENCE: 349 NM SOUTH OF KADENA AB
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 12 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
RAGGED, DISORGANIZED CIRCULATION, WITH CONVECTION FLARING AND
EXTENDING IN A LINEAR BAND TO THE SOUTHWEST OF THE OBSCURED LOW LEVEL
CIRCULATION CENTER (LLCC). THE CIRCULATION IS WEAK ENOUGH TO NOT BE
CLEARLY EVIDENT EVEN IN THE MOST RECENT 200919Z SSMIS 91GHZ
MICROWAVE IMAGE. THE AGENCY FIX POSITIONS ARE THUS SPREAD OVER A
WIDE SWATH COVERING OVER 75NM, THUS THE INITIAL POSITION IS
ASSESSED WITH LOW CONFIDENCE. THE INITIAL POSITION IS LIKEWISE
ASSESSED WITH LOW CONFIDENCE, AS THERE IS A FULL T-NUMBER SPREAD
BETWEEN THE SUBJECTIVE AGENCY DVORAK CURRENT INTENSITY ESTIMATES,
AND THE OBJECTIVE ADT EXTREMELY HIGH BASED ON THE OVERALL
APPEARANCE OF THE SYSTEM AT PRESENT. ADDITIONAL CONFIDENCE WAS
PROVIDED HOWEVER BY THE DEEP MICRONET AND OPEN-AIIR ESTIMATES, BOTH
OF WHICH WERE BETWEEN 23 TO 25 KNOTS. LATE RECEIPT OF A PARTIAL
201324Z ASCAT-B PASS SHOWS THE HIGHLY ASYMMETRICAL NATURE OF THE
CIRCULATION, WITH STRONG (25-30 KNOT) NORTHEASTERLY STRAIGHT LINE
WINDS TO THE NORTHWEST AND VERY LIGHT WINDS (10 KNOTS OR LESS) ON
THE SOUTH AND EAST SIDE OF THE ELONGATED CIRCULATION CENTER. THE
SYSTEM IS TRAVERSING WEST-SOUTHWESTWARD THROUGH A GENERALLY
FAVORABLE ENVIRONMENT, BUT CONTINUES TO STRUGGLE TO CONSOLIDATE AND
OVERCOME THE INTRUSION OF RELATIVELY DRIER AND MORE STABLE AIR
ASSOCIATED WITH STRONG NORTHEASTERLY SURGE FLOW PUNCHING IN ON THE
WEST SIDE.

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

CURRENT STEERING MECHANISM: SOUTH-SOUTHEAST PERIPHERY OF A
DEEP-LAYER SUBTROPICAL RIDGE (STR) CENTERED OVER TAIWAN. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   RJTD: T1.0 - 25 KTS
   KNES: T2.0 - 30 KTS
   CIMSS ADT: 37 KTS AT 201140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD
   OTHER FACTORS: ENTRAINMENT OF RELATIVELY STABLE, DRY AIR INTO
THE NORTHWESTERN SIDE OF THE CIRCULATION. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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: AFTER HAVING TRACKED GENERALLY WESTWARD OVER
THE PREVIOUS 12 HOURS OR SO, TD 25W HAS NOW BEGUN TRACKING MORE
SOUTHWESTWARD AS EXPECTED, AS THE STR OVER TAIWAN HAS BEGUN TO BUILD
TOWARDS THE NORTHEAST. OVER THE NEXT 12 HOURS, THIS RIDGE IS
FORECAST TO QUICKLY MORPH INTO A LARGE EAST-WEST ORIENTED RIDGE
COMPLEX EXTENDING FROM SOUTHERN CHINA TO EAST OF OKINAWA. TD 25W
WILL ASSUME A NEARLY DUE WEST TRACK AFTER TAU 12 ALONG THE SOUTHERN
SIDE OF THIS RIDGE AXIS. A VERY SLIGHT JOG POLEWARD IS POSSIBLE
AROUND TAU 36 AS A WEAK TROUGH PASSES TO THE NORTH AND INDUCES A
WEAKNESS IN THE RIDGE, THOUGH THE TROUGH WILL BE TOO WEAK TO EXERT
MUCH OF AN INFLUENCE ON TD 25W. THE SYSTEM IS EXPECTED TO PASS
THROUGH THE LUZON STRAIT AND EMERGE INTO THE SOUTH CHINA SEA BY TAU
48. AT THIS POINT THE SYSTEM WILL REACH AN INFLECTION POINT WHEREBY
THE PRIMARY STEERING MECHANISM WILL SWITCH OVER TO THE STR
ENSCONCED OVER SOUTHERN CHINA, INDUCING A SOUTHWESTWARD TRACK
THROUGH THE REMAINDER OF THE FORECAST PERIOD. BASED ON THE VERY
RECENT ASCAT DATA, THE SYSTEM REMAINS HIGHLY ASYMMETRICAL WITH AN
ELONGATED LLCC. THUS, IT HAS A SIGNIFICANT MOUNTAIN TO CLIMB BEFORE
SIGNIFICANT INTENSIFICATION CAN BEGIN AND THE SYSTEM IS EXPECTED TO
INTENSIFY VERY SLOWLY THROUGH THE NEXT 24 HOURS AS A RESULT.
CONDITIONS WILL IMPROVE AROUND TAU 36, AS THE SYSTEM IS ANTICIPATED
TO BE WELL-CONSOLIDATED BY THAT POINT, AND THE UPPER-LEVEL OUTFLOW
IMPROVES, ALLOWING FOR A FASTER PACE OF INTENSIFICATION, TO A PEAK
OF 60 KNOTS BY TAU 72. AFTER TAU 72, UPPER-LEVEL CONVERGENT
EASTERLY FLOW, AND DECREASING SSTS LEFT IN THE WAKE OF TY 23W WILL
CONSPIRE TO STEADILY WEAKEN THE SYSTEM THROUGH TAU 120.  

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE, WITH THE EXCEPTION
OF NAVGEM, IS IN GOOD AGREEMENT THROUGH TAU 72, WITH THE REMAINDER
OF THE GUIDANCE CONSTRAINED IN A 60NM ENVELOPE AS THE SYSTEM
CROSSES THE LUZON STRAIT, EXPANDING OUT TO AN 80NM ENVELOPE BY
TAU 72. THE JTWC FORECAST LIES GENERALLY CLOSE TO THE CONSENSUS
MEAN THROUGH TAU 72, WITH MEDIUM CONFIDENCE. AFTER TAU 72, THE
GUIDANCE GETS SQUIRRELLY, WITH THE TRACKERS SHOWING A VERY WIDE
SPREAD OF 400NM BY TAU 120, EVEN WHEN DISCOUNTING THE NAVGEM
TRACKER. THE GFS TRACKS THE SYSTEM SHARPLY WESTWARD AFTER TAU 96
TOWARDS THE SOUTHERN GULF OF TONKIN, WHILE THE GALWEM AND UKMET
TURN THE SYSTEM SHARPLY SOUTHWARD TO A POSITION EAST OF SOUTHERN
VIETNAM DURING THE SAME TIMEFRAME. THE JTWC TRACK LIES CLOSE TO THE
ECMWF TRACKER, TO THE NORTH OF THE CONSENSUS MEAN WHICH IS BEING
PULLED TOO FAR SOUTH BY THE NAVGEM, UKMET AND GALWEM TRACKERS, WITH
LOW CONFIDENCE. THE PEAK IN THE INTENSITY GUIDANCE HAS PICKED UP
WITH THIS RUN, WITH THE HWRF AND GFS NOW UP TO 70 KNOTS, WHILE THE
COAMPS-TC REMAINS UNEXCITED ABOUT THE SYSTEM, WITH A PEAK INTENSITY
OF ONLY 40 KNOTS. THE JTWC FORECAST CLOSELY ALIGNS WITH THE HWRF
SOLUTION THROUGH THE FORECAST PERIOD WITH MEDIUM CONFIDENCE.   

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