WDXS31 PGTW 110900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING 
NR 011//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.3S 121.8E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 217 NM NORTH OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTH-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 23 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN EXPANDING
CENTRAL DENSE OVERCAST (CDO) MEASURING 250NM ACROSS THAT HAS FULLY
OBSCURED THE LOW LEVEL CIRCULATION CENTER. NEAR NEW DAY ZULU THE
SYSTEM WAS BRIEFLY EXPOSED REVEALING TIGHTLY WRAPPING LOW LEVEL
CLOUD LINES. A FORTUITOUS 110539Z AMSR2 37GHZ COLOR COMPOSITE
MICROWAVE IMAGE REVEALS CONSOLIDATING BANDING FEATURES TO THE
EAST AND WEST OF THE LLCC WHILE THE CORE OF THE SYSTEM CONTINUES TO
FORM. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED
ON THE AMSR2 IMAGERY. THE INITIAL INTENSITY OF 55 KTS IS ASSESSED
WITH MEDIUM CONFIDENCE BASED ON CIMSS SATCON AND ADT INDICATING CLOSER
TO 55KTS WHILE AGENCY DVORAK INTENSITY ESTIMATES LAG BEHIND DUE TO
THE CHANGING SCENE TYPE AND CONSTRAINTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE EAST

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.0 - 45 KTS
   KNES: T3.0 - 45 KTS
   APRF: T3.0 - 45 KTS
   CIMSS SATCON: 52 KTS AT 110529Z
   CIMSS ADT: 53 KTS AT 110530Z

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

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 FORECAST TO CONTINUE SOUTHWESTWARD
UNDER THE STEERING INFLUENCE OF THE STR TO THE EAST. BY TAU 12 AND
THROUGH TAU 36, THE ENVIRONMENT AROUND 18S WILL SHIFT FROM
FAVORABLE TO A HIGHLY FAVORABLE, CHARACTERIZED BY WARM SSTS
(30-31C), LOW VERTICAL WIND SHEAR AND IMPROVING OUTFLOW ALOFT. AS
THE SYSTEM APPROACHES THE STR AXIS NEAR TAU 36, THE SYSTEM IS
FORECAST TO BE NEAR 105KTS. AS 18S BEGINS TO TURN POLEWARD AND
EVENTUALLY SOUTH-SOUTHEASTWARD, SST AND OHC VALUES COMBINED WITH
ROBUST OUTFLOW ALOFT WILL FUEL 18S TO A PEAK INTENSITY OF 120KTS
AND POSSIBLY HIGHER BEFORE MAKING LANDFALL NEAR THE CENTER POINT OF
EIGHTY MILE BEACH. AFTER PROGRESSING INLAND, THE SYSTEM WILL
QUICKLY WEAKEN OVER AUSTRALIA AND EVENTUALLY DISSIPATE NEAR TAU 96.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIR AGREEMENT THAT 18S
WILL ROUND THE STR AXIS AND MAKE LANDFALL BETWEEN BROOME AND PORT
HEDLAND WITH A 100NM SPREAD IN SOLUTIONS BY LANDFALL. AS A RESULT
THE JTWC TRACK FORECAST IS PLACED WITH MEDIUM CONFIDENCE. RELIABLE
MODEL INTENSITY GUIDANCE IS IN FAIR AGREEMENT WITH ALL MEMBERS
INDICATING AN INTENSIFICATION TREND THROUGH TAU 48 AFTER WHICH 
INTESNITY SHARPLY DECLINES THROUGH THE FORECAST PERIOD. DURING THE 
INITIAL INTENSIFICATION, SEVERAL RAPID INTENSIFICATION (RI) AIDS ARE
TRIGGERING WITH DECAY-SHIPS PEAKING NEAR 85KTS WHILE COAMPS-TC
(NAVGEM VERSION) AND GFS PEAK NEAR 135KTS. GIVEN THE HIGH OHC AND
SST VALUES, MORE CREDENCE IS GENERALLY PLACED IN OCEAN COUPLED
MODELS SUCH AS COAMPS AND HWRF WHICH BOTH RETURN PEAK INTENSITIES
NORTH OF 100KTS BY TAU 48. FOR THESE REASONS THE JTWC INTENSITY
FORECAST IS PLACED WITH MEDIUM CONFIDENCE.

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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