WDPS31 PGTW 281500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 23P (URMIL) WARNING NR 
008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 21.1S 173.2E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 344 NM SOUTHEAST OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY REVEALS TROPICAL
CYCLONE (TC) 23P (URMIL) WITH ITS COMPLETELY OBSCURED LOW-LEVEL
CIRCULATION CENTER (LLCC), EMBEDDED WITHIN A CENTRAL DENSE OVERCAST
(CDO). A LOW-TO-MODERATE (15-20 KTS) WESTERLY VERTICAL WIND SHEAR
(VWS) IS INDUCING A PRONOUNCED ASYMMETRY IN THE CONVECTIVE STRUCTURE, 
THEREBY BEGINNING TO DISPLACE THE PRIMARY DEEP CONVECTIVE MASS TO THE 
SOUTHEAST OF THE CENTER. DESPITE THIS, A ROBUST UPPER-LEVEL OUTFLOW 
ARCHITECTURE REMAINS ESTABLISHED PRIMARILY THROUGHOUT THE POLEWARD 
QUADRANTS. FURTHER ENVIRONMENTAL ANALYSIS INDICATES THAT THE SYSTEM IS 
SITUATED OVER A REGION OF FAVORABLY WARM (27-28 C) SEA SURFACE 
TEMPERATURES (SSTS), OFFSET HOWEVER BY THE INCREASING INTRUSION OF A 
DRIER, MID-TROPOSPHERIC AIR FROM THE WEST AND NORTH. THE INITIAL 
POSITION IS RENDERED WITH HIGH CONFIDENCE, BASED ON A 281141Z GPM GMI 
MICROWAVE IMAGERY SUITE. THE INITIAL INTENSITY OF 65 KTS IS ASSESSED 
WITH MEDIUM CONFIDENCE, DERIVED FROM A SYNTHESIS OF THE AVAILABLE 
OBJECTIVE AND SUBJECTIVE ESTIMATES LISTED BELOW.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T4.0 - 65 KTS
   PHFO: T4.5 - 77 KTS
   CIMSS ADT: 59 KTS AT 281130Z
   CIMSS AIDT: 65 KTS AT 281130Z
   CIMSS D-MINT: 34 KTS AT 281142Z
   CIMSS D-PRINT: 59 KTS AT 281200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE WEST AND NORTH

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC URMIL IS FORECAST TO MAINTAIN A SOUTHEASTWARD 
TRAJECTORY THROUGHOUT THE CURRENT FORECAST, GOVERNED BY THE DEEP-LAYER 
STEERING FLOW ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE 
TO ITS EAST. THE ENVIRONMENTAL CONDITIONS ARE PROJECTED TO BE MARGINAL 
AND ALLOWING FOR SOME MINOR INTENSIFICATION AS INDICATED BY AN 
EXPECTED PEAK INTENSITY OF 70 KTS REACHED WITHIN THE NEXT 12 HOURS. 
AROUND OR PRIOR TO TAU 24, THE CYCLONE IS EXPECTED TO BEGIN TO PHASE 
WITH A TRANSIENT UPPER-LEVEL TROUGH, A PROCESS THAT WILL INITIATE A 
SUBTROPICAL TRANSITION (STT). A PRONOUNCED AMPLIFICATION OF THE VWS IS
PROJECTED, REACHING 40+ KTS BY TAU 36. THIS WILL OCCUR CONCURRENTLY
WITH THE SYSTEM TRANSITING OVER A DECREASING OCEANIC HEAT CONTENT
GRADIENT, WITH SSTS FORECAST TO FALL BELOW 26 C. COUPLED WITH 
AGGRESSIVE DRY AIR ENTRAINMENT, THIS WILL INITIATE A SUSTAINED
ATTENUATION TREND. THE STT IS FORECAST TO CONCLUDE BY TAU 36, AS TC
23P BECOMES FULLY EMBEDDED WITHIN THE BAROCLINIC ZONE OF THE
PROPAGATING LONGWAVE TROUGH.

MODEL DISCUSSION: A HIGH DEGREE OF CONGRUENCE IS EVIDENT AMONGST
THE NUMERICAL TRACK GUIDANCE, WITH NEGLIGIBLE LATITUDINAL AND
LONGITUDINAL DISPERSION. THIS SUPPORTS A HIGH-CONFIDENCE ASSESSMENT
FOR THE OFFICIAL JTWC TRACK FORECAST, WHICH IS LAID CLOSE TO THE
MULTI-MODEL CONSENSUS, LEANING CLOSE TO THE GUIDANCE FROM ECMWF
AND ECMWF ENSEMBLE, WHICH PROVED TO INITIALIZE BEST DURING THE
MOST RECENT ANALYSIS. WITH RESPECT TO INTENSITY, A MINOR DEGREE OF
DISCREPANCY EXISTS IN THE INITIAL 12 HOURS OF ANALYSIS, WITH GFS AND 
STATISTICAL-DYNAMICAL MODELS PRESENTING A MORE CONSERVATIVE, SLIGHTLY 
WEAKENING TREND. HAFS, HWRF, COAMPS-TC AND GFS ON THE OTHER HAND ALLOW 
ROOM FOR MINOR BUMP IN INTENSITY REACHING 70 KTS. ALL GUIDANCE IS 
UNIFIED IN DEPICTING A WEAKENING PHASE OVER THE FOLLOWING 24 HOURS, 
WITH A TIGHTLY-PACKED ENVELOPE EXHIBITING ONLY A 5 KT SPREAD. 
COINCIDENT WITH THE ONSET OF STT, THE ULTIMATE DISSIPATION OF TC
23P IS EXPECTED TO OCCUR BEYOND THE CURRENT FORECAST PERIOD.
ACCORDINGLY, THE OFFICIAL JTWC INTENSITY FORECAST IS RENDERED WITH
OVERALL MEDIUM CONFIDENCE.

FORECAST CONFIDENCE:
   TRACK 00-72 HR: HIGH
   INTENSITY 00-72 HR: MEDIUM//
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