WDXS32 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN)
WARNING NR 005//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 13.4S 106.1E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 702 NM NORTHWEST OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: EASTWARD AT 06 KTS
   SIGNIFICANT WAVE HEIGHT: 20 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL
CYCLONE (TC) 18S (EIGHTEEN) WITH AN EXPOSED AND ELONGATED LOW-LEVEL
CIRCULATION CENTER (LLCC) HAVING DEEP CONVECTION DISPLACED TO THE
WEST-NORTHWEST OF THE CIRCULATION CENTER. A 120244Z ASCAT-C IMAGE
REVEALS THE ELONGATED NATURE OF THE CIRCULATION WITH 40 KTS WINDS IN
THE NORTHWESTERN QUADRANT. ENVIRONMENTAL ANALYSIS INDICATES THAT
18S IS IN A MARGINALLY FAVORABLE ENVIRONMENT FOR FURTHER
DEVELOPMENT WITH MODERATE OUTFLOW ALOFT, MODERATE TO HIGH (20-25 KTS)
VERTICAL WIND SHEAR, OFFSET BY WARM (28-29 C) SSTS. THE INITIAL 
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE LLCC BEING 
EXPOSED AND EASILY IDENTIFIABLE IN ANIMATED IMAGERY AND A 120600Z 
HIMAWARI-9 VISIBLE SATELLITE IMAGE. THE INITIAL INTENSITY OF 40 KTS 
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PREVIOUSLY MENTIONED 
ASCAT IMAGE.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   CIMSS SATCON: 43 KTS AT 120554Z
   CIMSS ADT: 33 KTS AT 120530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 CURRENTLY TRACKING EASTWARD ALONG
THE SOUTHERN PERIPHERY OF A NER TO THE NORTH. AT TAU 48, TC 18S IS
FORECAST TO MAKE A POLEWARD TURN AS A RIDGE OVER WESTERN
AUSTRALIA BLOCKS THE SYSTEM FROM CONTINUING THE EASTWARD TRACK AND 
TURNS THE SYSTEM SOUTHWARD THROUGH TAU 72. AFTER TAU 72, TC 18S IS 
FORECAST TO CONTINUE TURNING TO A SOUTHWESTWARD TRACK BY TAU 120. THE
SYSTEM IS FORECASTED TO MAINTAIN A GRADUAL INTENSIFICATION TREND
THROUGHOUT THE FORECAST PERIOD DUE TO VWS VALUES BEGINNING TO
DECREASE BELOW 20 KTS AFTER TAU 12 AND UPPER-LEVEL DIVERGENCE
IMPROVING OUTFLOW ALOFT.

MODEL DISCUSSION: GLOBAL NUMERICAL MODEL GUIDANCE IS IN FAIR
AGREEMENT REGARDING TRACK AND GOOD AGREEMENT REGARDING INTENSITY. A
SIGNIFICANT CROSS-TRACK SPREAD OF APPROXIMATELY 503NM IS PRESENT BY
TAU 72, INDICATING MUCH UNCERTAINTY ON HOW FAR EAST THE SYSTEM
TRACKS BEFORE MAKING A TURN TO A SOUTHWESTWARD TRACK BY TAU 120. THE 
JTWC FORECAST TRACK ALIGNS CLOSELY WITH THE ECMWF DETERMINISTIC AND
ENSEMBLE GUIDANCE, WITH GFS THE FURTHEST EAST OF THE CONSENSUS
MEMBERS AND GALWEM THE FURTHEST WEST. INTENSITY GUIDANCE SUGGESTS
A GRADUAL RISE IN INTENSITY THROUGH TAU 120 AS THE ENVIRONMENT GROWS 
MORE FAVORABLE. WITH THE EXCEPTION OF COAMPS-TC, THE INTENSITY SPREAD 
IS GREATEST AMONG CONSENSUS MEMBERS NEAR TAU 96 WITH A 30 KTS SPREAD 
IN GUIDANCE.

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