WDXS31 PGTW 100900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN)   
WARNING NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.1S 122.9E
   INITIAL INTENSITY: 45 KTS
   GEOGRAPHIC REFERENCE: 746 NM NORTHEAST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 18S WAS REPOSITIONED 50NM NNE AT 100000Z
BASED ON A 100124Z ASCAT-B IMAGE SHOWING A BROAD, DEFINED
CIRCULATION WITH A SWATH OF 25-30 KNOT WINDS OVER THE SOUTHERN
QUADRANT. CONSEQUENTLY, THIS SHIFTED THE FORECAST TRACK NORTH
CLOSER TO THE KNES AND APRF POSITION FIXES. THE INITIAL POSITION IS
CONSISTENT WITH THE ASCAT-B IMAGE AND CURRENT ANIMATED
MULTISPECTRAL SATELLITE IMAGERY, WHICH DEPICTS A PARTIALLY EXPOSED
LOW-LEVEL CIRCULATION CENTER (LLCC) POSITIONED ON THE NORTHEAST
EDGE OF A LARGE CONVECTIVE CLUSTER DUE TO NORTHEASTERLY VERTICAL
WIND SHEAR (VWS). A 100752Z GMI 89GHZ COLOR COMPOSITE MICROWAVE IMAGE 
REVEALS SHALLOW BANDING WRAPPING INTO A RAGGED LLCC. PREVIOUS PGTW 
POSITION FIXES WERE LOCATED WITHIN CONVERGENT EASTERLY LOW-LEVEL FLOW 
AND THE ASSOCIATED DEEP CONVECTION YIELDING ERRONEOUSLY HIGH DATA-T 
NUMBERS. THERE IS MEDIUM CONFIDENCE IN THE INITIAL INTENSITY DUE TO 
POSITIONAL UNCERTAINTY, HOWEVER, IT IS CONSERVATIVELY ASSESSED AT 45 
KNOTS BASED ON THE APRF AND CIMSS SATCON ESTIMATES AS WELL AS THE 
OPEN-AIIR ESTIMATE OF 45 KNOTS.   

INITIAL WIND RADII BASIS: OBJECTIVE BEST TRACK 

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR)
POSITIONED TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   KNES: T3.5 - 55 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 46 KTS AT 100548Z
   CIMSS ADT: 49 KTS AT 100530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 15-20 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: MODERATE POLEWARD AND EQUATORWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: LOW
   INITIAL INTENSITY: MEDIUM
   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 EXPECTED TO TRACK SOUTHWESTWARD TO 
SOUTHWARD THROUGH TAU 72 AS IT ROUNDS THE STR. TC 18S HAS STRUGGLED TO 
CONSOLIDATE DUE TO THE VWS, HOWEVER, VWS WILL DECREASE AS THE SYSTEM 
TRACKS POLEWARD OVER THE NEXT 12 TO 24 HOURS, WHICH WILL ALLOW THE 
SYSTEM TO RAPIDLY INTENSIFY THROUGH LANDFALL NEAR TAU 72. 
ADDITIONALLY, HIGH OCEAN HEAT CONTENT NEAR THE AUSTRALIAN COAST AND 
ENHANCED POLEWARD OUTFLOW WILL ALLOW THE SYSTEM TO PEAK NEAR 130 KNOTS 
BY TAU 72. AFTER TAU 72, TC 18S WILL ACCELERATE SOUTHEASTWARD AS IT 
INTERACTS WITH A MAJOR SHORTWAVE TROUGH AND WILL WEAKEN RAPIDLY OVER 
LAND.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH A 210NM CROSS-TRACK SPREAD IN SOLUTIONS AT TAU 72 REFLECTING 
UNCERTAINTY IN THE RECURVE POINT. AFTER TAU 72, CROSS-TRACK SPREAD 
DECREASES, HOWEVER, ALONG TRACK UNCERTAINTY INCREASES AS THE SYSTEM 
INTERACTS WITH THE AFOREMENTIONED SHORTWAVE TROUGH AND ACCELERATES 
SOUTHEASTWARD. THE RAPID INTENSIFICATION CONSENSUS (RICN) GUIDANCE HAS 
TRIGGERED SUPPORTING RAPID INTENSIFICATION (RI) OVER THE NEXT TWO 
DAYS. ADDITIONALLY, THE 100000Z COAMPS TC ENSEMBLE (CTCXEPS) CONTINUES 
TO INDICATE A 100 PERCENT PROBABILITY OF RI FROM TAU 30 TO TAU 72 
SUPPORTING THE RI FORECAST IN THE DAY 2 TO DAY 3 PERIOD. 

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