WDXS32 PGTW 131500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN)
WARNING NR 010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.3S 111.5E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 445 NM NORTH-NORTHWEST OF LEARMONTH,
   AUSTRALIA
   MOVEMENT PAST 6 HOURS: EAST-SOUTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED IMAGERY (EIR) DEPICTS TROPICAL CYCLONE
(TC) 18S (EIGHTEEN) WITH A PARTIALLY EXPOSED AND INCREASINGLY 
DISORGANIZED LOW-LEVEL CIRCULATION CENTER. DUE TO HIGH EASTERLY SHEAR 
OVER THE SYSTEM, A WESTWARD TILTING VORTEX AND INTERMITTENT BURSTS OF 
CONVECTION INDICATE THE SYSTEM IS STRUGGLING TO TAP INTO GOOD OUTFLOW 
ALOFT. ENVIRONMENTAL ANALYSIS INDICATES THAT 18S IS IN A MARGINAL 
ENVIRONMENT FOR FURTHER INTENSIFICATION WITH WEAK TO MODERATE 
POLEWARD OUTFLOW ALOFT, HIGH (25-30 KTS) VERTICAL WIND SHEAR, OFFSET 
BY WARM (29-30 C) SEA SURFACE TEMPERATURES. THE INITIAL POSITION IS 
PLACED WITH LOW CONFIDENCE BASED ON A 131200Z HIMAWARI-9 EIR IMAGE. 
THE INITIAL INTENSITY IS ALSO PLACED WITH LOW CONFIDENCE BASED ON THE 
OBJECTIVE AND SUBJECTIVE INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SOUTHERN PERIPHERY OF A NEAR EQUATORIAL
RIDGE (NER) TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T1.5 - 25 KTS
   CIMSS ADT: 32 KTS AT 131200Z
   CIMSS AIDT: 33 KTS AT 131200Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 25-30 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK TO MODERATE POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: LOW
   INITIAL WIND RADII: LOW

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TC 18S IS CURRENTLY TRACKING SOUTHEASTWARD
ALONG THE SOUTHERN PERIPHERY OF A NER TO THE NORTH. TC 18S IS
FORECAST TO CONTINUE THIS TRACK UNTIL TAU 36, WHERE IT IS
ANTICIPATED TO INITIATE A POLEWARD TURN IN RESPONSE TO A
SUBTROPICAL RIDGE (STR) POSITIONED OVER WESTERN AUSTRALIA. THE SYSTEM 
IS FORECAST TO HAVE COMPLETED THE POLEWARD TURN NEAR TAU 72. AFTER 
TAU 72, TC 18S IS EXPECTED TO CONTINUE ON A SOUTHWESTWARD TRACK FOR 
THE REMAINDER OF THE FORECAST PERIOD. REGARDING THE INTENSITY 
FORECAST, TC 18S IS FORECAST TO MAINTAIN 35 KTS THROUGH TAU 12 DUE TO 
THE RELATIVELY DISORGANIZED STRUCTURE AND MARGINAL ENVIRONMENT. AFTER 
TAU 12, TC 18S IS FORECAST TO THEN GRADUALLY INCREASE INTENSITY 
THROUGHOUT THE DURATION OF THE FORECAST PERIOD AS THE SYSTEM TRACKS 
INTO A MARGINALLY FAVORABLE ENVIRONMENT WITH MORE CONDUCIVE VERTICAL
WIND SHEAR WITH VALUES (10-15 KTS) STARING AT TAU 36 AND
SEA SURFACE TEMPERATURES REMAINING VERY WARM.  

MODEL DISCUSSION: GLOBAL NUMERICAL MODEL GUIDANCE IS IN FAIR 
AGREEMENT WITH A CROSS-TRACK SPREAD OF 325 NM AT TAU 72. GFS 
CONTINUES TO BE AN OUTLYING MODEL, TRACKING THE SYSTEM FURTHER EAST 
BEFORE STARTING THE POLEWARD TURN PREVIOUSLY DISCUSSED. THE JTWC 
TRACK FORECAST ALIGNS CLOSELY WITH ECMWF DETERMINISTIC AND ENSEMBLE 
MEMBER SOLUTIONS. MODEL GUIDANCE REMAINS FAIRLY DIVIDED REGARDING THE 
TIMING AND SHARPNESS OF THE POLEWARD TURN, AND AS SUCH, THE JTWC
FORECAST TRACK IS PLACED WITH OVERALL LOW CONFIDENCE. INTENSITY
GUIDANCE IS IN BETTER ALIGNMENT - RELATIVE TO TRACK AGREEMENT - WITH 
THE EXCEPTION OF COAMPS-TC. BY TAU 48, ALL JTWC INTENSITY CONSENSUS 
MEMBERS SUGGEST THAT TC 18S WILL INTENSIFY THROUGH TAU 120. THERE IS 
A 20 KT SPREAD IN THE INTENSITY GUIDANCE THAT PERSISTS FOR THE 
MAJORITY OF THE FORECAST INTERVAL, LENDING OVERALL MEDIUM CONFIDENCE 
IN THE JTWC INTENSITY FORECAST.

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