WDPS31 PGTW 041500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 23P (TWENTYTHREE) 
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.3S 162.1E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 356 NM WEST OF PORT VILA, VANUATU
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS IMPROVED
DEEP CONVECTIVE BANDING OVER THE EASTERN SEMICIRCLE WITH AN
IRREGULAR CENTRAL DENSE OVERCAST (CDO) OBSCURING THE LOW-LEVEL
CIRCULATION CENTER, WHICH APPEARS TO BE LOCATED JUST UNDER THE
WESTERN EDGE OF THE CDO. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON THE EIR IMAGERY. SOUTHERLY VERTICAL WIND SHEAR
(VWS) HAS DECREASED SLIGHTLY OVER THE PAST SIX HOURS ALLOWING DEEP
CONVECTION TO EXPAND OVER THE SOUTHWEST QUADRANT WHILE UPPER-LEVEL
OUTFLOW REMAINS RADIAL ENHANCED BY STRONG WESTERLIES TO THE SOUTH.
ADDITIONALLY, SEA SURFACE TEMPERATURES OF 29-30C ARE CONDUCIVE FOR
FURTHER DEVELOPMENT. THE INITIAL INTENSITY OF 40 KTS IS HEDGED
ABOVE AGENCY DVORAK ESTIMATES BASED ON THE INCREASING ADT ESTIMATES 
OF 39 TO 45 KNOTS FROM 041140Z TO 041340Z. SURFACE OBSERVATIONS FROM
ILE SURPRISE (91570), ABOUT 90NM SOUTHEAST OF THE CENTER, INDICATE
25-30 KNOT (10-MINUTE AVERAGE) NORTHEASTERLY WINDS WITH SLP NEAR
1005MB, WHICH SUGGESTS GALE FORCE WINDS HAVE WRAPPED AROUND THE
SOUTHERN QUADRANT.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) POSITIONED TO
THE EAST AND SOUTHEAST 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   FMEE: T2.5 - 35 KTS
   CIMSS ADT: 39 KTS AT 041140Z (45 KNOTS AT 041340Z)

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

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 23P IS FORECAST TO SLOW
AND TURN SHARPLY SOUTH-SOUTHEASTWARD OVER THE NEXT 06-12 HOURS AS
THE STR TO THE SOUTH SHIFTS EASTWARD AND REALIGNS IN RESPONSE TO AN
APPROACHING UPPER-LEVEL SHORTWAVE TROUGH. TC 23P WILL RAPIDLY
INTENSIFY (RI) OVER THE NEXT 24 HOURS TO A PEAK OF 65 KNOTS AT TAU
24 DUE PRIMARILY TO ROBUST UPPER-LEVEL OUTFLOW. AFTER TAU 24, TC
23P WILL CONTINUE TRACKING SOUTH-SOUTHEASTWARD THROUGH THE FORECAST 
PERIOD ALONG THE WESTERN PERIPHERY OF THE STR. TC 23P SHOULD 
GRADUALLY WEAKEN THROUGH THE REMAINDER OF THE FORECAST PERIOD AS THE 
SYSTEM TRACKS UNDER SUBTROPICAL WESTERLIES AND ENVIRONMENTAL 
CONDITIONS DEGRADE. TC 23P WILL BEGIN SUBTROPICAL TRANSITION NEAR 
TAU 72 AS IT BEGINS TO INTERACT WITH A BAROCLINIC ZONE SOUTH OF NEW 
CALEDONIA AND TRACKS OVER COOLER SST (25-26C). ADDITIONALLY, VWS 
WILL INCREASE TO HIGHER LEVELS (30-50 KNOTS) AS THE SYSTEM 
TRANSITIONS INTO A SUBTROPICAL CYCLONE BY TAU 120. THE SYSTEM IS 
EXPECTED TO SLOW IN THE EXTENDED PERIOD AS IT WEAKENS TO 45 KNOTS 
AND RUNS INTO A STRONG HIGH 
EXPECTED TO BUILD OVER AND NORTH OF NEW ZEALAND.

MODEL DISCUSSION: THERE IS CURRENTLY A BIFURCATION IN THE MODEL
GUIDANCE WITH ECMWF AND THE ECMWF ENSEMBLE MEAN INDICATING A MORE
PROLONGED SOUTHWESTWARD TRACK BEFORE TURNING SOUTHWARD WHILE THE
REMAINDER OF THE GUIDANCE IS SHOWING A TRACK OVER OR TO THE WEST OF
NEW CALEDONIA. THE ECMWF SOLUTION IS ASSESSED AS UNLIKELY SINCE IT
TRACKS THE SYSTEM DIRECTLY INTO THE SUBTROPICAL WESTERLIES BEFORE
STALLING IT AND TURNING IT SOUTHWARD WITHIN THE SUBTROPICAL
WESTERLIES. THE 040600Z ECMWF ENSEMBLE CONTINUES TO SHOW A WIDER
RANGE OF TRACK POSSIBILITIES WITH A STRONGER TC TRACKING CLOSER TO
NEW CALEDONIA AND A WEAKER TC MUCH FURTHER WEST. THE 040600Z
COAMPS-TC ENSEMBLE (GFS VERSION) INDICATES A HIGH PROBABILITY
(70-100 PERCENT) OF RI OCCURRING OVER THE NEXT 36 HOURS, WHICH
SUPPORTS THE JTWC INTENSITY FORECAST. OVERALL CONFIDENCE IN THE
JTWC TRACK AND INTENSITY FORECAST IS MEDIUM.   

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