WDPS31 PGTW 280900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 23P (URMIL) WARNING NR 
007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 20.8S 171.7E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 268 NM SOUTHEAST OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 22 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 23P (URMIL) WITH A FULLY OBSCURED LOW-LEVEL CIRCULATION. 
LOW TO MODERATE (15-20 KTS) WESTERLY VERTICAL WIND SHEAR (VWS) IS 
LIMITING THE WESTERN EXTENT OF THE CONVECTIVE CANOPY, BUT POLEWARD AND 
EQUATORWARD OUTFLOW CHANNELS REMAIN STRONG. ADDITIONAL ENVIRONMENTAL 
ANALYSIS REVEALS WARM (27-28 C) SEA SURFACE TEMPERATURES (SST) AND 
GOOD AMOUNTS OF AVAILABLE ATMOSPHERIC MOISTURE THROUGHOUT THE VERTICAL 
COLUMN. SOME DRIER AIR IS HOWEVER BEGINNING TO ENTRAIN THE VORTEX FROM 
THE WEST AND NORTH. THE INITIAL POSITION IS PLACED WITH MEDIUM 
CONFIDENCE BASED ON EXTRAPOLATION FROM A 280232Z GW1 AMSR2 MICROWAVE 
SUITE. THE INITIAL INTENSITY OF 65 KTS IS ALSO ASSESSED WITH MEDIUM 
CONFIDENCE AND IS BASED ON A BLEND OF OBJECTIVE AND SUBJECTIVE 
INTENSITY AIDS 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: T3.5 - 55 KTS
   KNES: T4.0 - 65 KTS
   PHFO: T4.5 - 77 KTS
   CIMSS SATCON: 56 KTS AT 280219Z
   CIMSS ADT: 63 KTS AT 280530Z
   CIMSS AIDT: 53 KTS AT 280530Z
   CIMSS D-MINT: 56 KTS AT 280625Z
   CIMSS D-PRINT: 56 KTS AT 280630Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: STRONG POLEWARD AND EQUATORWARD

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

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 CONTINUE TRACKING
SOUTHEASTWARD THROUGHOUT THE CURRENT FORECAST PERIOD, UNDER THE
PRIMARY INFLUENCE OF A STR CENTERED TO THE EAST. THE ENVIRONMENT IS
EXPECTED TO REMAIN MARGINALLY FAVORABLE FOR DEVELOPMENT OVER THE
NEXT 12-24 HOURS, RESULTING IN POTENTIAL FOR SOME SLIGHT (5-10 KTS)
INTENSIFICATION. AROUND TAU 24, THE SYSTEM WILL GET CLOSER TO A
PASSING UPPER-LEVEL TROUGH AND BEGIN ITS SUBTROPICAL TRANSITION
(STT). THE VWS WILL BEGIN TO RAPIDLY INCREASE, REACHING NEARLY 50
KTS AT TAU 36. SIMULTANEOUSLY, SSTS ARE EXPECTED TO DECREASE BELOW
26 C, WHICH COMBINED WITH INCREASED DRY AIR INTRUSION WILL RESULT IN
THE BEGINNING OF A WEAKENING TREND. THE SUBTROPICAL TRANSITION IS
EXPECTED TO COMPLETE AT TAU 36, AS TC 23P BECOMES FULLY EMBEDDED
WITHIN A EQUATORWARD EXTENSION OF A PASSING UPPER-LEVEL TROUGH, WHILE
MAINTAINING RELATIVELY HIGH (60-65 KTS) SURFACE WIND SPEEDS.

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT IN REGARD TO THE TRACK, WITH MINIMAL CROSS-TRACK AND
ALONG-TRACK VARIABILITY, RESULTING IN HIGH CONFIDENCE IN THE OFFICIAL 
JTWC FORECAST. AS FAR AS INTENSITY, THERE IS SOME UNCERTAINTY 
ASSOCIATED WITH THE INITIAL MAXIMUM WIND SPEED AMONG THE MODELS, WITH 
COAMPS-TC AND GFS BEING A BIT MORE CONSERVATIVE THAN OTHER MEMBERS OF 
THE CONSENSUS. ALL MODELS INDICATE POTENTIAL FOR INTENSIFICATION OVER 
THE NEXT 24 HOURS, WITH JUST 10 KTS OF THE GUIDANCE SPREAD. AFTER TAU 
24, NEARLY ALL MODELS SUGGEST RAPID WEAKENING AS THE SYSTEM BEGINS ITS 
STT, WITH DISSIPATION BEYOND THE CURRENT FORECAST PERIOD. AS SUCH, THE 
JTWC OFFICIAL INTENSITY FORECAST IS LAID WITH MEDIUM CONFIDENCE.

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