WDPS31 PGTW 291500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (EIGHTEEN) WARNING 
NR 006//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 26.2S 172.5E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 428 NM SOUTHEAST OF NOUMEA, NEW CALEDONIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 14 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 18P WITH A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION
CENTER (LLCC) THAT IS NOW VOID OF DEEP CONVECTION. STRONG NORTHERLY
SHEAR AND DRY AIR ENTRAINMENT CONTINUE TO ACT ON THE VORTEX,
INHIBITING THE DEVELOPMENT OF CONVECTION. THE INITIAL POSITION IS
PLACED WITH LOW CONFIDENCE DUE TO THE CENTER BEING SOMEWHAT
OBSCURED BY THE CIRRUS CLOUDS FLOWING OVER THE SYSTEM IN ANIMATED
EIR IMAGERY. THE INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE AGENCY DVORAK FIXES AND OBJECTIVE
INTENSITY ESTIMATES LISTED BELOW. THE STRONGEST WINDS ARE CONFINED
TO THE EASTERLIES THAT MAKE UP THE SOUTHERN SEMICIRCLE OF THE
CIRCULATION. ENVIRONMENTAL ANALYSIS INDICATES THAT 18P REMAINS IN
AN UNFAVORABLE ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW
ALOFT GREATLY OFFSET BY SIGNIFICANT DRY AIR ENTRAINMENT, HIGH
(30-35 KTS) NORTHERLY VERTICAL WIND SHEAR, AND MARGINAL (25-26 C)
SEA SURFACE TEMPERATURES.

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

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


AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 32 KTS AT 291210Z
   CIMSS AIDT: 38 KTS AT 291140Z
   CIMSS D-PRINT: 41 KTS AT 291210Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30-35 KTS
   SST: 25-26 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: SIGNIFICANT DRY AIR ENTRAINMENT FROM THE NORTH

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   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 18P IS FORECAST TO TRACK GENERALLY
SOUTHWESTWARD OVER THE NEXT 24 HOURS AS AN EXTENSION OF THE STR TO
THE EAST JUTS UNDERNEATH THE VORTEX. THE UNFAVORABLE ENVIRONMENT IS
EXPECTED TO PERSIST OVER THE NEXT 24 HOURS WITH STRONG NORTHERLY
SHEAR AND SIGNIFICANT DRY AIR ENTRAINMENT FROM THE NORTH. THESE TWO
FACTORS WILL CONTRIBUTE TO A CONTINUED WEAKENING TREND. 18P IS
FORECAST TO WEAKEN BELOW TC STRENGTH NEAR TAU 12 AS THE SHALLOW
VORTEX DRIFTS OFF TO THE SOUTHWEST. 18P IS ANALYZED TO BE
SIMULTANEOUSLY GOING THROUGH SUBTROPICAL TRANSITION AS IT
DISSIPATES. 18P IS FORECAST TO COMPLETE SUBTROPICAL TRANSITION AT
AROUND THE SAME TIME THAT IT WEAKENS BELOW TC STRENGTH.  

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH NO NOTABLE OUTLIERS. THE SHORT JTWC TRACK FORECAST
IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE IS ALSO IN GOOD AGREEMENT WITH ALL MODEL SHOWING
WEAKENING OVER THE NEXT 24 HOURS. THE JTWC INTENSITY FORECAST IS
ALSO PLACED NEAR THE CONSENSUS WITH HIGH CONFIDENCE.

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