WDPN31 PGTW 241500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 12W (KROSA) 
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.2N 143.5E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 141 NM WEST-NORTHWEST OF TINIAN
   MOVEMENT PAST 6 HOURS: NORTHWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 15 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
DEPRESSION (TD) 12W (KROSA) AS A STRUGGLING CYCLONE WITH A
COMPLETELY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WHILE
CONVECTION HAS REMAINED LARGELY DISLOCATED AWAY FROM THE ASSESSED
CENTER DUE TO HIGH WIND SHEAR VALUES OF OVER 30 KTS. NEAR THE
SURFACE, FRAGMENTED CURVED CLOUD LINES HAVE BEEN OBSERVED WRAPPING
AROUND AN ASYMMETRIC WIND FIELD OVER THE PAST FEW HOURS. ALOFT,
ANIMATED WATER VAPOR IMAGERY HAS CONTINUED TO SHOW MODERATE BUT
DISORGANIZED POLEWARD OUTFLOW WITH NO DEFINITIVE ASSOCIATED SUPPORT
CHANNELS. WITH REGARD TO THE ENVIRONMENTAL ANALYSIS, ALTHOUGH SEA
SURFACE TEMPERATURES REMAIN WARM (29-30 C) AND UPPER-LEVEL OUTFLOW
MODERATE, VERTICAL WIND SHEAR (VWS) HAS REMOVED SUPPORTIVE
CONVECTIVE STRUCTURES AWAY FROM THE CENTRAL VORTEX. THE INITIAL
POSITION HAS BEEN PLACED WITH HIGH CONFIDENCE BASED ON A RECENT
241045Z ASCAT IMAGE. THE INITIAL INTENSITY IS ASSESSED WITH HIGH
CONFIDENCE BASED ON THE AFOREMENTIONED ASCAT DATA AND SUBJECTIVE
DVORAK ESTIMATES LISTED BELOW.

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: T1.0 - 25 KTS
   RJTD: T1.5 - 25 KTS
   RCTP: T1.5 - 25 KTS
   KNES: T1.0 - 25 KTS
   CIMSS ADT: 33 KTS AT 241230Z
   CIMSS AIDT: 36 KTS AT 241230Z
   CIMSS D-MINT: 22 KTS AT 240822Z
   CIMSS D-PRINT: 25 KTS AT 241230Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 30+ KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 12W IS EXPECTED TO CONTINUE ON A GENERALLY
NORTHWARD TRACK THROUGHOUT THE 120 HOUR FORECAST PERIOD. IN THE
SHORT-TERM, A BUILDING SUBTROPICAL RIDGE TO THE EAST WILL INITIATE
SLIGHT VARIATIONS IN THE AFOREMENTIONED TRACK, WITH A
NORTH-NORTHEASTWARD MOVEMENT BETWEEN TAU 0 AND TAU 48. FOLLOWING
TAU 48, TD 12W WILL APPROACH THE WEAKER NORTHWESTERN EXTENT OF THE
STEERING RIDGE AND BEGIN TRACKING NORTH-NORTHWESTWARD UNTIL TAU
120. AT THE SAME TIME, A BUILDING RIDGE EXTENDING FROM THE
NORTHWEST PACIFIC INTO THE SEA OF JAPAN WILL GRADUALLY SLOW
NORTHWARD MOVEMENT BY TAU 120. WITH REGARD TO INTENSITY, TD 12W IS
EXPECTED TO STEADILY INTENSIFY OVER THE NEXT 72 HOURS DUE TO
UPPER-LEVEL SUPPORT FROM AN EASTWARD MOVING SHORTWAVE TROUGH,
PROVIDING AN ORGANIZED UPPER-LEVEL OUTFLOW MECHANISM WITHIN A
LARGELY MARGINAL TO FAVORABLE ENVIRONMENT. BETWEEN TAU 60 AND TAU
72, AN AREA OF CYCLONIC TURNING ALOFT WILL BEGIN INTRODUCING
ADDITIONAL DRY-AIR AROUND THE CENTRAL VORTEX, LIMITING FURTHER TC
DEVELOPMENT. DURING THE LENGTH OF THE FORECAST AFTER TAU 72, A
SOUTHWEST TO NORTHEAST ORIENTED SWATH OF ENHANCED WINDS IN CLOSE
PROXIMITY TO TD 12W WILL AID IN A SLOW AND STEADY WEAKENING PHASE
UNTIL THE END OF THE FORECAST PERIOD.

MODEL DISCUSSION: NUMERICAL WEATHER PREDICTION (NWP) GUIDANCE IS IN
GOOD AGREEMENT THROUGH THE INITIAL 72 HOURS OF THE FORECAST PERIOD,
WITH A FEW OUTLIER TRACKS ON THE WESTWARD AND EASTWARD EXTENT OF
THE CONSENSUS ENVELOPE. NAVGEM COVERS THE EASTWARD EXTENT, WHILE
THE UKMET DETERMINISTIC SOLUTION DRIVES THE SYSTEM WESTWARD.
BETWEEN TAU 72 AND TAU 120, THE MAJORITY OF THE NWP SOLUTIONS
WITHIN THE CONSENSUS ARE ALIGNED, WITH THE EXCEPTION OF THE ECMWF
ENSEMBLE MEAN TRACKING ALONG THE WESTWARD EXTREME UNTIL THE END OF
THE FORECAST PERIOD WITH INDICATIONS OF TRACK SOLUTION BIFURCATION
AT TAU 120, LENDING TO THE LOW CONFIDENCE BETWEEN TAU 72 AND TAU
120. THE JTWC TRACK FORECAST IS ALIGNED CLOSELY WITH THE JTWC
CONSENSUS TRACK, AS THE OVERALL TRACK HAS EDGED SLIGHTLY EASTWARD
AFTER TAU 72 HOURS OVER THE LAST SIX HOURS. WITH REGARD TO
INTENSITY, THERE IS ALSO GOOD AGREEMENT THAT STEADY INTENSIFICATION
TO 60 KTS IS EXPECTED UNTIL TAU 72. THERE IS CURRENTLY ONLY ONE
OUTLIER (COAMPS-TC), INDICATING A MAXIMUM INTENSITY OF 70 KTS AT
TAU 72. AFTER TAU 72, ALL INTENSITY SOLUTIONS SHOW A GRADUAL
WEAKENING PHASE UNTIL THE END OF THE FORECAST. ALTHOUGH THE JTWC
INTENSITY FORECAST IS ALIGNED CLOSELY WITH THE CONSENSUS, THE LOW
CONFIDENCE BETWEEN TAU 72 AND TAU 120 IS DUE TO THE OBSERVED
BIFURCATION IN THE LATER STAGES OF THE TRACK FORECAST MODEL SOLUTIONS.

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