WDXS32 PGTW 141500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN)  
WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0S 115.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 332 NM NORTH-NORTHEAST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 16 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 18S HAS SHOWN SIGNS OF INCREASED
CONSOLIDATION AS VERTICAL WIND SHEAR (VWS) HAS DECREASED IN CLOSE
PROXIMITY TO THE CENTRAL CORE AND THE ONCE FULLY-EXPOSED CENTER HAS
BECOME COMPLETELY OBSCURED BY INCREASED FLARING CONVECTION OVER THE
LOW-LEVEL CIRCULATION CENTER (LLCC), AS REVEALED IN THE ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY. MODERATE EQUATORWARD
OUTFLOW IS NOW EVIDENT OVER THE SURFACE CIRCULATION, AS UPPER-LEVEL
OUTFLOW HAS CONTINUED TO AID IN THE OVERALL CONSOLIDATION OF THE
SYSTEM THROUGHOUT THE LAST SIX HOURS. THE INITIAL POSITION IS
PLACED WITH MEDIUM CONFIDENCE BASED ON A 141106Z 37 GHZ SSMIS
MICROWAVE IMAGE. AN EARLIER 140202Z ASCAT-C IMAGE HAS SHOWN AN
ASYMMETRIC WIND FIELD WITH A SWATH OF 35 KNOT WINDS TO THE NORTH,
WHICH SUPPORTS THE INITIAL INTENSITY ASSESSMENT OF 35 KNOTS WITH
MEDIUM CONFIDENCE. AGENCY SUBJECTIVE DVORAK ESTIMATES CONTINUE TO
REMAIN SLIGHTLY LOWER AT 30 KNOTS, WITH UW-CIMSS ADT AND AIDT
ESTIMATES RANGING BETWEEN 29 TO 31 KNOTS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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
   DEMS: T2.0 - 30 KTS
   APRF: T1.5 - 25 KTS
   CIMSS ADT: 29 KTS AT 141200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE EQUATORWARD

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: TC 18S IS FORECAST TO TRACK SOUTHEASTWARD
THROUGH TAU 12. HOWEVER, THE SYSTEM IS EXPECTED TO CONTINUE SLOWING
DOWN AND GRADUALLY TURN SOUTHWARD TO SOUTHWESTWARD THROUGH TAU 42
AS THE AFOREMENTIONED WESTWARD 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 CONTINUE DECREASING, ALLOWING THE SYSTEM TO CONSOLIDATE
FURTHER. AFTER TAU 48, TC 18S WILL TRACK SLOWLY SOUTH-SOUTHWESTWARD
TOWARD A BREAK IN THE STR STEERING PATTERN ASSOCIATED WITH AN
APPROACHING SHORTWAVE TROUGH AND FRONTAL SYSTEM. AFTER TAU 90, A
STRONG LOW-LEVEL HIGH IS EXPECTED TO BUILD TO THE SOUTH OVER
WESTERN AUSTRALIA, EFFECTIVELY BLOCKING AND SLOWING POLEWARD
PROGRESSION. AFTER TAU 66, ENVIRONMENTAL CONDITIONS APPEAR
INCREASINGLY CONDUCIVE, WITH LOW VWS AND IMPROVING POLEWARD OUTFLOW
INTO THE MIDLATITUDE EQUATORWARD-EXTENDING SHORTWAVE TROUGH, WHICH
WILL RESULT IN MODERATE INTENSIFICATION TO A PEAK INTENSITY OF 70
KNOTS BY TAU 96 AND THROUGH THE REMAINDER OF THE FORECAST PERIOD. 

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM AND THE ECMWF ENSEMBLE 
MEAN, DETERMINISTIC NUMERICAL MODEL TRACK GUIDANCE REMAINS IN FAIR 
AGREEMENT THROUGH TAU 72 WITH A 117 NM CROSS-TRACK SPREAD AT TAU 72 
THEN POOR AGREEMENT AFTER TAU 72 WITH A 254 NM CROSS-TRACK SPREAD AT 
TAU 120. THE 140600Z ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) ALSO 
INDICATE CONTINUED AND INCREASING UNCERTAINTY AFTER TAU 72, WITH A 
VERY LARGE SPREAD IN SOLUTIONS. THE 140600Z COAMPS-TC INTENSITY 
ENSEMBLE (CTCXEPS) SHOWS INCREASING INTENSITY PROBABILITIES OF 
MODERATE INTENSIFICATION, WITH PEAK PROBABILITY VALUES RANGING FROM 50 
TO 80 PERCENT FROM TAU 54 TO TAU 90. RAPID INTENSIFICATION 
PROBABILITIES REMAIN LOW AT LESS THAN 25 PERCENT THROUGHOUT THE 120 
HOUR FORECAST. 

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