WDPS31 PGTW 270300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 23P (URMIL) WARNING NR 
002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.6S 167.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 59 NM SOUTH-SOUTHWEST OF PORT VILA,
VANUATU
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHEASTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE 23P (URMIL) WITH A HIGHLY COMPACT CORE OF DEEP CONVECTION
THAT HAS STARTED TO ENCIRCLE THE ASSESSED CENTER. A 262257Z GMI 89
GHZ MICROWAVE IMAGE SHOWED A SMALL HOOK FEATURE ASSOCIATED WITH THE
CORE OF THE SYSTEM, REVEALING THE COMPACT NATURE OF THE SYSTEM. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A SHORT
EXTRAPOLATION FROM THE GMI IMAGE. THE INITIAL INTENSITY OF 45 KTS
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES
AND CIMSS INTENSITY ESTIMATES LISTED BELOW. ENVIRONMENTAL ANALYSIS
INDICATES THAT 23P IS IN A HIGHLY FAVORABLE ENVIRONMENT CHARACTERIZED 
BY STRONG POLEWARD OUTFLOW ALOFT, LOW (5-10 KTS) VERTICAL WIND SHEAR, 
AND WARM (28-29 C) SEA SURFACE TEMPERATURES (SST).

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SOUTHWESTERN PERIPHERY OF A SUBTROPICAL
RIDGE (STR) CENTERED OVER FIJI

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   PHFO: T3.0 - 45 KTS
   NFFN: T3.0 - 45 KTS
   CIMSS ADT: 49 KTS AT 270030Z
   CIMSS AIDT: 34 KTS AT 270030Z
   CIMSS D-MINT: 46 KTS AT 262301Z
   CIMSS D-PRINT: 53 KTS AT 270030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 5-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

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

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: INCREASED THE NEAR-TERM INTENSITY,
SHOWING A MUCH QUICKER RATE OF INTENSIFICATION OVER THE NEXT 24
HOURS THAN THE PREVIOUS FORECAST

FORECAST DISCUSSION: TC 23P IS FORECAST TO TRACK
EAST-SOUTHEASTWARD, ALONG THE SOUTHWESTERN PERIPHERY OF THE STR
THROUGH TAU 48. 23P IS NOW FORECAST TO MAKE LANDFALL OVER TANNA
ISLAND JUST AFTER TAU 12. NEAR TAU 48, THE RIDGE IS EXPECTED TO
PROPAGATE EASTWARD AND REORIENT INTO A NORTHWEST-SOUTHEAST
ORIENTATION, FURTHER GUIDING THE VORTEX SOUTHEASTWARD THROUGH TAU
72. REGARDING INTENSITY, 23P IS FORECAST TO QUICKLY INTENSIFY OVER
THE NEXT 24 HOURS AS THE ENVIRONMENT REMAINS FAVORABLE. THE HIGHLY
COMPACT NATURE OF THE SYSTEM WILL LIKELY AID IN THE RAPID OR
NEAR-RAPID RATE OF INTENSIFICATION. NEAR TAU 24, DRY AIR
ENTRAINMENT FROM THE WEST WILL HINDER THE INTENSIFICATION RATE,
THOUGH OTHER ENVIRONMENTAL VARIABLES ARE EXPECTED TO REMAIN
FAVORABLE. THE PEAK INTENSITY IS FORECAST TO OCCUR NEAR TAU 48 AT
AROUND 80 KTS, HOWEVER, THAT IS HIGHLY DEPENDENT ON HOW MUCH THE
SYSTEM IS ABLE TO STRENGTHEN THROUGH TAU 24. IF THE COMPACT CORE OF
CONVECTION IS ABLE TO PERSIST, THEN A HIGHER INTENSITY IS POSSIBLE.
AFTER TAU 48, NORTHWESTERLY SHEAR IS EXPECTED TO QUICKLY INCREASE
AND DRY AIR ENTRAINMENT FROM THE WEST WILL FURTHER ERODE THE
SYSTEM. THESE TWO FACTORS WILL PUT A CAP ON THE INTENSIFICATION
TREND. BY TAU 60, NORTHWESTERLY SHEAR IS FORECAST TO BE NEAR 50
KTS, WHICH WILL ULTIMATELY CAUSE THE SYSTEM TO WEAKEN TO AROUND 60
KTS AT TAU 72.  SUBTROPICAL TRANSITION (STT) IS FORECAST TO BEGIN
NEAR TAU 48 WITH COMPLETION NO LATER THAN TAU 72 AS THE VORTEX
SHALLOWS, ELONGATES, AND BECOMES EMBEDDED WITHIN THE STRONG
UPPER-LEVEL FLOW. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH A CROSS-TRACK SPREAD
OF 90 NM AT TAU 72. ALONG TRACK SPREAD DOES INCREASE AFTER TAU 48
DUE TO THE DIFFERING INTERACTIONS WITH THE STRONG UPPER-LEVEL
WINDS. AT TAU 72, ALONG-TRACK SPREAD IS MEASURED TO BE AROUND 220
NM, SLIGHTLY DECREASING THE CONFIDENCE IN THE TAU 72 POSITION.
OVERALL, THE JTWC TRACK FORECAST IS PLACED NEAR THE MULTI-MODEL
CONSENSUS WITH HIGH CONFIDENCE. INTENSITY GUIDANCE HAS BECOME SPLIT
BETWEEN RAPID INTENSIFICATION (RI) AIDS AND NON-RI AIDS. NEARLY ALL
AVAILABLE RI AID HAS TRIGGERED THIS MODEL RUN AND THE AI-RI OUTPUT
FROM CIMSS IS SHOWING A 43 PERCENT CHANCE OF A 55 KNOT INCREASE IN
48 HOURS. ON THE OTHER HAND, MESOSCALE MODELS SUGGEST A MUCH LOWER
PEAK, RANGING FROM 65-75 KTS AT TAU 48. THE JTWC INTENSITY FORECAST
IS PLACED CLOSE TO THE RI AIDS THROUGH TAU 24, THEN ABOUT 10 KTS
HIGHER THAN THE CONSENSUS THROUGH TAU 48, CALLING FOR A PEAK OF 80
KTS, WITH LOW CONFIDENCE. MODELS THEN AGREE ON WEAKENING AFTER TAU
48. 

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