WDXS32 PGTW 111500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN)  
WARNING NR 002//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.0S 102.6E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 903 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: EASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 18S HAS CONTINUED TO STRUGGLE TO DEVELOP DUE
TO PERSISTENT HIGH (30-40 KNOTS) EASTERLY VERTICAL WIND SHEAR AS
EVIDENCED IN THE ANIMATED PROXYVIS SATELLITE IMAGERY. THE FULLY
EXPOSED LOW-LEVEL CIRCULATION (LLC) MENTIONED IN THE PREVIOUS 
FORECAST HAS BECOME COMPLETELY OBSCURED OVER THE LAST SIX HOURS BY 
FLARING CONVECTION ALONG THE WESTERN PERIPHERY OF THE CIRCULATION 
CENTER. HOWEVER, IMAGERY HAS RECENTLY REVEALED A BROAD, EXPOSED 
SURFACE CIRCULATION AROUND A PRIMARY CENTROID FEATURE. DEEP 
CONVECTION HAS REMAINED ISOLATED TO THE WESTERN EDGE OF THE LLC, 
WHILE LOW-LEVEL BANDING AND A BROAD CENTER ARE ALSO EVIDENT IN THE 
111149Z SSMIS 91 GHZ MICROWAVE IMAGE. AN 110634Z AMSR2 WINDSPEED 
IMAGE HAS CONTINUED TO CONFIRM A BROAD CENTER WITH EXTENSIVE GALE-
FORCE WINDS (35-45 KNOTS) DISPLACED ALONG THE NORTHWEST PERIPHERY. 
THIS EXTENSIVE WIND FIELD IS REFLECTED IN THE WIND RADII ANALYSIS. 
THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE 
AFOREMENTIONED 91 GHZ MICROWAVE PASS. THE INITIAL INTENSITY OF 40 KTS 
REMAINS ASSESSED WITH LOW CONFIDENCE BASED ON RECENT ASCAT AND AMSR2 
DATA.

INITIAL WIND RADII BASIS: PERSISTENCE AND RECENT SCATTEROMETER DATA.

CURRENT STEERING MECHANISM: NEAR-EQUATORIAL RIDGE (NER) POSITIONED
                            TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   DEMS: T2.0 - 30 KTS
   APRF: T2.0 - 30 KTS
   CIMSS ADT: 41 KTS AT 111130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 30-40 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

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

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 EAST-SOUTHEASTWARD 
THROUGH TAU 72 UNDER THE STRONG STEERING INFLUENCE OF THE NER.
AFTER TAU 72, THE SYSTEM WILL SLOW, POSSIBLY BECOMING QUASI-
STATIONARY AS THE STEERING INFLUENCE GRADUALLY TRANSITIONS TO A 
BUILDING STR OVER AUSTRALIA. THE SYSTEM IS EXPECTED TO TURN SOUTH-
SOUTHWESTWARD BY TAU 120 ALONG THE NORTHERN PERIPHERY OF THE 
AFOREMENTIONED STR WITHIN A COMPETING STEERING ENVIRONMENT. THE
SYSTEM WILL INTENSIFY SLOWLY THROUGH TAU 72 DUE TO PERSISTENT HIGH 
(25-35 KNOTS) EASTERLY VWS. AFTER TAU 72, THE SYSTEM WILL INTENSIFY 
AT A SLIGHTLY QUICKER RATE, HOWEVER, THE PEAK INTENSITY WILL REMAIN 
LIMITED DUE TO THE LACK OF A POLEWARD OUTFLOW MECHANISM.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN POOR AGREEMENT
WITH TWO DISTINCT GROUPS OF MODEL TRACKERS. THE FIRST GROUP COMPOSED 
OF NAVGEM, GALWEM, UKMET, AND THE UKMET ENSEMBLE MEAN ARE ON THE 
WESTERN SIDE OF THE AIDS ENVELOPE AND SHOW A SOUTHEASTWARD TRACK 
THROUGH TAU 72 THEN TURN SHARPLY SOUTHWARD THROUGH TAU 120. THE 
SECOND GROUP COMPOSED OF ECMWF, GFS, ECMWF ENEMBLE MEAN, AND THE
GFS ENSEMBLE MEAN INDICATE A MORE PROLONGED EAST-SOUTHEASTWARD
TRACK TOWARD ROWLEY SHOALS, AUSTRALIA BY TAU 96 THEN TURN SHARPLY TO
THE SOUTH-SOUTHWEST BY TAU 120. THE JTWC TRACK FORECAST PHILOSOPHY 
FAVORS THE SECOND GROUP OF NUMERICAL MODEL TRACKERS, WHICH INDICATE A 
MORE REALISTIC SOLUTION. THE 110600Z ECMWF ENSEMBLE AND THE 110000Z 
GFS ENSEMBLE REVEAL A SIMILAR WIDE SPREAD OF SOLUTIONS WITH TWO 
DISTINCT CLUSTERS, REFLECTING HIGH UNCERTAINTY THROUGH TAU 120. 
RELIABLE INTENSITY GUIDANCE INDICATES FAIR AGREEMENT THROUGH THE 
FORECAST PERIOD WITH A STEADY INTENSIFICATION TREND. 

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