WDPS31 PGTW 290900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18P (EIGHTEEN) WARNING 
NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 24.9S 173.0E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 415 NM EAST-SOUTHEAST OF NOUMEA, NEW
CALEDONIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 15 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 18P WITH A MOSTLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) AND A RAPIDLY WEAKENING CONVECTIVE STRUCTURE. THE STRONG
NORTHERLY SHEAR ACTING ON THE SYSTEM CONTINUES TO DISPLACE
CONVECTION FAR TO THE SOUTH OF THE CENTER. A 290621Z WSFM 89 GHZ
MICROWAVE IMAGE REVEALED THE EXPOSED LOW-LEVEL CLOUDS WRAPPING INTO
THE ASSESSED CENTER WITH A DISTINCT WEAKNESS IN THE NORTHERN
PORTION OF THE LLCC. THE INITIAL POSITION IS PLACED WITH MEDIUM
CONFIDENCE BASED ON THE WSFM IMAGE AND ANIMATED MSI. THE INITIAL
INTENSITY OF 45 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE
AGENCY DVORAK FIXES AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.
ENVIRONMENTAL ANALYSIS INDICATES THAT 18P IS NOW IN AN UNFAVORABLE
ENVIRONMENT CHARACTERIZED BY STRONG POLEWARD OUTFLOW ALOFT AND
WARMISH (26-27 C) SEA SURFACE TEMPERATURES GREATLY OFFSET BY DRY
AIR ENTRAINMENT AND HIGH NORTHERLY VERTICAL WIND SHEAR.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   CIMSS SATCON: 48 KTS AT 290400Z
   CIMSS ADT: 47 KTS AT 290600Z
   CIMSS AIDT: 41 KTS AT 290600Z
   CIMSS D-MINT: 41 KTS AT 290624Z
   CIMSS D-PRINT: 40 KTS AT 290600Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 30-35 KTS
   SST: 26-27 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT FROM THE NORTH

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: 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 AROUND TAU 24 AS THE SHALLOW
VORTEX DRIFTS OFF TO THE SOUTHWEST. 18P IS EXPECTED TO SIMULTANEOUSLY 
BEGIN SUBTROPICAL TRANSITION AS IT DISSIPATES, HOWEVER, THE SYSTEM IS 
FORECAST TO DISSIPATE BEFORE SUBTROPICAL TRANSITION CAN FULLY 
COMPLETE. 

MODEL DISCUSSION: NUMERICAL MODEL TRACK GUIDANCE IS IN GOOD
AGREEMENT WITH AN 85 NM CROSS-TRACK SPREAD AT TAU 24. 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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