WDPS31 PGTW 270900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 23P (URMIL) WARNING NR 
003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 19.4S 168.5E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 103 NM SOUTH OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A VERY
COMPACT TROPICAL CYCLONE (TC), POSITIONED JUST WEST OF TANNA
ISLAND, VANUATU. ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A
SMALL INNER CORE OF DEEP, COLD CONVECTION, WITH ISOLATED OVERSHOOTING 
TOPS ALONG THE SOUTHERN AND EASTERN PERIPHERY OF THE LOW-LEVEL 
CIRCULATION CENTER (LLCC). THE UPPER-LEVEL VORTEX IS SITUATED ON THE 
MARGINS OF RADAR RANGE FROM NEW CALEDONIA AND CORRESPONDING 
REFLECTIVITY DATA INDICATES AN INTERMITTENT EYE FEATURE WITH 
CONVECTIVE BURSTS ALONG THE SOUTHERN PERIPHERY OF THE INNER CORE. THE 
SYSTEM HAS TURNED EAST-SOUTHEASTWARD OVER THE PAST HOURS BASED ON 
RADAR ANALYSIS AND IS NOW TRACKING TOWARDS TANNA ISLAND. LATE RECEIPT 
OF A 270640Z SSMIS PASS SUGGESTS THE LLCC MAY BE DISPLACED 
APPROXIMATELY 15NM TO THE NORTHWEST OF THE INITIAL POSITION, WHICH 
WAS ASSESSED WITH LOW CONFIDENCE BASED ON MSI, EIR, AND GROUND-BASED 
RADAR DATA. THIS REVISED POSITION ALIGNS THE STORM TRACK WITH 
OBSERVED MOTION, INDICATING A MORE EASTWARD VICE SOUTHEASTWARD. THE 
SSMIS 91GHZ MICROWAVE DATA INDICATES MODERATE WESTERLY SHEAR BENEATH 
THE OUTFLOW LAYER, WITH DEEP CONVECTIVE MASS SHEARED EAST OF THE 
LLCC. THE INITIAL INTENSITY IS ASSESSED WITH HIGH CONFIDENCE BASED ON 
TIGHT CLUSTERING OF SUBJECTIVE AND OBJECTIVE ESTIMATES. ENVIRONMENTAL 
CONDITIONS ARE CONDUCIVE FOR DEVELOPMENT, WITH LOW DEEP-LAYER 
VERTICAL WIND SHEAR (VWS), ROBUST POLEWARD OUTFLOW, AND WARM SSTS, 
PARTIALLY TEMPERED BY MODERATE MID-LEVEL SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A DEEP-LAYER
SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   PHFO: T3.5 - 55 KTS
   NFFN: T3.0 - 45 KTS
   CIMSS SATCON: 53 KTS AT 270520Z
   CIMSS ADT: 55 KTS AT 270600Z
   CIMSS AIDT: 45 KTS AT 270600Z
   CIMSS D-MINT: 52 KTS AT 270238Z
   CIMSS D-PRINT: 55 KTS AT 270600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: MODERATE MID-LEVEL WESTERLY VERTICAL WIND SHEAR
(VWS) AND DRY MID-LEVEL AIR ALONG THE NORTHERN FLANK.

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: IN THE NEAR-TERM, TC 23P (URMIL) IS FORECAST TO 
TRANSIT OVER OR IN THE IMMEDIATE VICINITY OF TANNA ISLAND. AFTER 
CROSSING THE ISLAND, TC 23P WILL CURVE SOUTHEASTWARD ALONG THE 
SOUTHWESTERN GRADIENT OF A DEEP-LAYER STR POSITIONED NORTHWEST OF 
FIJI. FROM TAU 24 THROUGH THE END OF THE FORECAST PERIOD, THE STR 
WILL PROPAGATE SOUTHEASTWARD, REMAINING IN PHASE WITH TC 23P, 
MAINTAINING A VIGOROUS STEERING GRADIENT AND ACCELERATING URMIL 
SOUTHEASTWARD THROUGH TAU 72. REGARDING INTENSITY, THE SYSTEM 
MAINTAINS AN INTENSIFICATION TREND DESPITE VORTEX TILT INDUCED BY 
MODERATE MID-LEVEL SHEAR. OROGRAPHIC INTERACTION WITH TANNA ISLAND 
MAY BRIEFLY ATTENUATE INTENSIFICATION; HOWEVER, UPON RE-EMERGENCE 
OVER OPEN WATER, THE SYSTEM IS EXPECTED TO ACHIEVE VERTICAL COHERENCE 
AND COMMENCE A MORE RAPID INTENSIFICATION PHASE. VWS IS FORECAST TO 
REMAIN LOW, WHILE UPPER-LEVEL OUTFLOW STEADILY AUGMENTS THROUGH TAU 
36, FACILITATING A PEAK INTENSITY OF 80 KNOTS. THEREAFTER, SHEAR 
MAGNITUDE IS FORECAST TO INCREASE PRECIPITOUSLY AS THE SYSTEM 
INTERACTS WITH THE SUBTROPICAL JET STREAK. BY TAU 48, THE SYSTEM WILL 
BE ENGULFED BY MID-LEVEL DRY AIR ENTRAINMENT AS IT TRANSITS POLEWARD 
OF THE 26C SST ISOTHERM, INITIATING SUBTROPICAL TRANSITION (STT) 
CONCURRENT WITH RAPID WEAKENING. COMPLETION OF STT IS ANTICIPATED BY 
TAU 60 AND WILL BE FINALIZED BY TAU 72.

MODEL DISCUSSION: DETERMINISTIC, ENSEMBLE AND ARTIFICIAL
INTELLIGENCE (AI) GUIDANCE IS IN STRONG AGREEMENT THROUGH THE
FORECAST PERIOD. HOWEVER, ONLY THE ECMWF CAPTURES THE SHORT-TERM 
EASTWARD DEFLECTION OVER TANNA ISLAND, WITH THE REMAINDER OF THE 
MULTI-MODEL CONSENSUS DEPICTING A SOUTHEASTWARD TRAJECTORY PASSING 
NEAR ANEITYUM ISLAND. CROSS-TRACK SPREAD EXPANDS TO A MAXIMUM OF 95NM 
AT TAU 48 BEFORE CONTRACTING SLIGHTLY THROUGH THE END OF THE PERIOD. 
THE JTWC FORECAST IS ALIGNED WITH THE ECMWF TRACKER, POSITIONED ON 
THE NORTHERN EDGE OF THE GUIDANCE ENVELOPE WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE IS MIXED; CTCX, COTC AND HWRF INDICATE A STAGNANT 
INTENSITY TREND THROUGH TAU 36 WITH MODEST STRENGTHENING TO 65-70 
KNOTS BY TAU 48. CONVERSELY, SHIPS GUIDANCE AND HAFS-A SUGGEST A MORE 
AGGRESSIVE DEVELOPMENT, PEAKING BETWEEN 80-95 KNOTS. ADDITIONALLY, 
THE FRIA, RIPA, AND RIDE RI AIDS ARE TRIGGERED, PROJECTING PEAK 
INTENSITIES OF 90-120 KNOTS. PROBABILISTIC GUIDANCE CONTINUES TO SHOW 
A 30-40 PERCENT CHANCE OF RI THROUGH TAU 48. THE JTWC FORECAST 
REMAINS CONSERVATIVE, ALIGNING WITH SHIPS OUTPUT JUST BELOW THE 
THRESHOLD FOR EXPLICIT RI. HOWEVER, THE COMPACT MORPHOLOGY OF THE 
VORTEX RENDERS THE SYSTEM SUSCEPTIBLE TO HIGH-AMPLITUDE INTENSITY 
FLUCTUATIONS.  

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