WDXS32 PGTW 140900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING NR 013// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.2S 115.0E INITIAL INTENSITY: 35 KTS GEOGRAPHIC REFERENCE: 370 NM NORTH OF LEARMONTH, AUSTRALIA MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 13 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 18S CONTINUES TO STRUGGLE UNDER HIGH VERTICAL WIND SHEAR AND REMAINS WELL-DEFINED AND FULLY-EXPOSED AS REVEALED IN THE ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI). THEREFORE, THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE. A 140202Z ASCAT-C IMAGE SHOWS AN ASYMMETRIC WIND FIELD WITH A SWATH OF 35 KNOT WINDS TO THE NORTH, WHICH SUPPORTS THE INITIAL INTENSITY ASSESSMENT OF 35 KNOTS WITH HIGH CONFIDENCE. AGENCY SUBJECTIVE DVORAK ESTIMATES REMAIN SLIGHTLY LOWER AT 30 KNOTS, WITH UW-CIMSS ADT AND AIDT ESTIMATES RANGING BETWEEN 34 TO 35 KNOTS. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) ENTRENCHED TO THE NORTH, WITH A BUILDING SUBTROPICAL RIDGE (STR) TO THE SOUTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.0 - 30 KTS KNES: T2.0 - 30 KTS APRF: T2.0 - 30 KTS CIMSS SATCON: 43 KTS AT 140159Z CIMSS ADT: 34 KTS AT 140600Z CIMSS AIDT: 35 KTS AT 140600Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL VWS: 25-30 KTS SST: 30-31 CELSIUS OUTFLOW: MODERATE WESTWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH 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 18S IS FORECAST TO TRACK SOUTHEASTWARD THROUGH TAU 12. HOWEVER, THE SYSTEM WILL SLOW AND GRADUALLY TURN SOUTHWARD TO SOUTHWESTWARD THROUGH TAU 72 AS THE AFOREMENTIONED BUILDING STR TO THE SOUTH BECOMES THE DOMINANT STEERING INFLUENCE. TC 18S IS FORECAST TO MAINTAIN WEAK TROPICAL STORM STRENGTH THROUGH TAU 48 DUE TO THE MARGINAL UPPER-LEVEL CONDITIONS. AFTER TAU 48, VERTICAL WIND SHEAR (VWS) IS EXPECTED TO DECREASE ALLOWING THE SYSTEM TO CONSOLIDATE. AFTER TAU 72, TC 18S WILL ACCELERATE SLIGHTLY AS IT TRACKS SOUTH-SOUTHWESTWARD TOWARD A BREAK IN THE STR ASSOCIATED WITH AN APPROACHING SHORTWAVE TROUGH AND FRONTAL SYSTEM. AFTER TAU 96, A STRONG LOW-LEVEL HIGH IS EXPECTED TO BUILD TO THE SOUTH OVER WESTERN AUSTRALIA EFFECTIVELY BLOCKING AND SLOWING POLEWARD PROGRESSION. AFTER TAU 72, ENVIRONMENTAL CONDITIONS APPEAR CONDUCIVE, WITH LOW VWS AND IMPROVING POLEWARD OUTFLOW INTO THE MIDLATITUDE SHORTWAVE TROUGH, WHICH WILL LEAD TO MODERATE INTENSIFICATION TO A PEAK INTENSITY OF 70 KNOTS BY TAU 96. MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, DETERMINISTIC NUMERICAL MODEL GUIDANCE REMAINS IN FAIR AGREEMENT WITH A 165 NM CROSS-TRACK SPREAD AT TAU 72 AND 245 NM AT TAU 120. THE 140000Z ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) ALSO INDICATE INCREASING UNCERTAINTY AFTER TAU 72, WITH A VERY LARGE SPREAD IN SOLUTIONS. THE 140000Z COAMPS-TC INTENSITY ENSEMBLE (CTCXEPS) SHOWS INCREASING INTENSITY PROBABILITIES OF MODERATE INTENSIFICATION, WITH PEAK PROBABILITY VALUES RANGING FROM 60 TO 90 PERCENT FROM TAU 54 TO TAU 100. RAPID INTENSIFICATION PROBABILITIES REMAIN LOW AT LESS THAN 30 PERCENT AFTER TAU 48. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN