WDPS31 PGTW 042100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 23P (TWENTYTHREE) 
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.9S 161.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 382 NM NORTHWEST OF NOUMEA, NEW CALEDONI
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 12 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ALTHOUGH ENHANCED INFRARED (EIR) SATELLITE IMAGERY REVEALS THE
SIGNIFICANT EFFECTS OF WESTERLY VERTICAL WINDSHEAR ON THE
CONVECTION ASSOCIATED WITH THE SYSTEM, IT IS STILL MANAGING TO RAMP
UP IN AN OTHERWISE VERY FAVORABLE ENVIRONMENT. THE LATEST
SHORTWAVE IR IMAGERY SHOWS A PARTIALLY EXPOSED LOW LEVEL
CIRCULATION CENTER (LLCC) TIGHTENING UP AND GENERATING PLENTY OF
DEEP CONVECTION OVER THE EASTERN SEMICIRCLE OF THE STORM.
SUBJECTIVE DVORAKS, ALTHOUGH UNANIMOUS FROM FOUR DIFFERENT
AGENCIES, ARE LAGGING THE AUTOMATED ASSESSMENTS. THE CURRENT
INTENSITY IS WEIGHTED TOWARDS THE ADT. THE 04APR1200Z JTWC UPPER
LEVEL STREAMLINE ANALYSIS REVEALS A POINT SOURCE JUST EQUATORWARD
OF THE LLCC, WHICH IS PROVIDING EXCELLENT OUTFLOW TO THE SYSTEM.
TROPICAL CYCLONE 23S IS SQUEEZED BETWEEN TWO UPPER LEVEL RIDGES ON
EITHER SIDE AND HAS NOWHERE TO GO BUT POLEWARD ALONG THE ZONE OF
WEAKNESS BETWEEN THEM. AN UPPER LEVEL TROF MOVING OFF THE EAST
COAST OF AUSTRALIA IS ALSO AIDING IN DRAWING THE SYSTEM POLEWARD,
ALTHOUGH MODEL GUIDANCE HAS BEEN CLEAR THAT THE MID-LATITUDE TROF
WILL CONTINUE DOWNSTREAM WITHOUT MAKING LINKAGE TO THE SYSTEM. THE
WESTERLY SHEAR IS BEING CAUSED BY A VIGOROUS SUBTROPICAL JETSTREAM
RUNNING OVER THE CORAL SEA. TOTAL PRECIPITABLE WATER LOOPS VERIFY
THAT DESPITE THE SHEAR ALOFT THE SYSTEM REMAINS WELL-COCOONED IN
DEEP MOISTURE. MODELED CROSS SECTIONS INDICATE THAT THE ENVIRONMENT
WILL REMAIN SATURATED ALONG TRACK.

INITIAL WIND RADII BASIS: THE CIRA MULTI-PLATFORM WIND ANALYSIS. 

CURRENT STEERING MECHANISM: A ZONE OF WEAKNESS BETWEEN TWO LOBES OF
THE SUBTROPICAL RIDGE. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.5 - 35 KTS
   PHFO: T2.5 - 35 KTS
   NFFN: T2.5 - 35 KTS
   CIMSS SATCON: 50 KTS AT 041431Z
   CIMSS ADT: 47 KTS AT 041740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 12-18 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE EASTWARD

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: CURRENT SATELLITE ANIMATION INDICATES TROPICAL
CYCLONE (TC) 23P IS SLOWING AS IT APPORACHES THE TURN INTO ITS
SOUTH-SOUTHEASTWARD LEG. THE STEERING RIDGE WILL SHIFT IN RESPONSE
TO THE MID-LATITUDE TROF AND AS IT DOES SO IT WILL ENHANCE OUTFLOW,
AIDING THE STORM TO BRIEFLY RAMP UP TO TYPHOON INTENSITY JUST
BEFORE IT CROSSES THE 20TH LATITUDE. THERE IS INCREASING CERTAINTY
THAT THE SYSTEM WILL TAKE A TRACK ALONG THE WESTERN SIDE OF NEW
CALEDONIA, ALTHOUGH WINDFIELDS IN THE LEFT FRONT QUADRANT WILL STILL
IMPACT THE ISLAND AS WELL AS PILE UP SEAS.  BEGINNING NEAR TAU 48, 
VERTICAL WINDSHEAR WILL INCREASE TO NEAR 25KTS WHILE SEA SURFACE 
TEMPERATURES FALL TO NEAR 26C, INITIATING THE SUBTROPICAL TRANSITION 
PROCESS.  DURING THE SAME PERIOD, A STRONG SURFACE HIGH PRESSURE 
SYSTEM WILL CROSS TASMANIA AND ENTER INTO THE CORAL SEA AND ITS
ASSOCIATED H500 RIDGE WILL BLOCK THE SYSTEM AND ENABLE THE 
SUBTROPICAL TRANSITION PROCESS TO COMPLETE ITSELF. 

MODEL DISCUSSION: BOTH GFS AND ECMWF DETERMINISTIC MODELS HAVE BEEN
PROGGING THIS SCENARIO FOR OVER A WEEK, AND DURING THAT TIME HAVE
DONE NOTHING BUT TIGHTEN UP. GFS HAS BEEN PARTICULARLY IMPRESSIVE.
BOTH DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN EXCELLENT
AGREEMENT ON THE TRACK AND THE JTWC FORECAST STAYS CLOSE TO THE
MULTI-MODEL CONSENSUS. INTENSITY GUIDANCE IS ALSO IN ABOVE AVERAGE
AGREEMENT, ESPECIALLY ON TREND. ALL GUIDANCE SHOWS THE SYSTEM
CLIMBING THROUGH TAU 48 AND THEN BEGINNING A STEADY DOWNTREND
THEREAFTER. THE JTWC FORECAST FOLLOWS THE SAME TREND BUT STAYS
ABOVE THE MEAN DUE TO THE BETTER PERFORMING AIDS BEING ON THE HIGH
SIDE OF THE ENVELOPE. 

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