WDXS31 PGTW 120900
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (ILSA) WARNING NR 
015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.0S 119.5E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 192 NM NORTHWEST OF BROOME, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHWESTWARD AT 05 KTS
   SIGNIFICANT WAVE HEIGHT: 37 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LARGE
CONSOLIDATING CIRCULATION WITH TIGHTLY WRAPPING BANDS OF DEEP
CONVECTION IN ALL QUADRANTS. TC ILSA IS STRUGGLING TO FORM AN EYE
FEATURE AS VERTICAL HOT TOWERS (VHT) CAN BE SEEN ORBITING THE CORE.
DECENT MICROWAVE DATA IS HARD TO COME BY SO A 120514Z ATMS 165GHZ
MICROWAVE IMAGE MUST SUFFICE. THIS IMAGE INDICATES A DEEP
CONVECTIVE CORE STRUCTURE WITH A SINGLE STRONG CONVECTIVE BAND TO
THE SOUTH AND WEAKER FRAGMENTED BANDING TO THE NORTH AND WEST. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON MSI AND
ATMS IMAGERY. THE INITIAL INTENSITY OF 90 KTS IS ASSESSED WITH
MEDIUM CONFIDENCE BASED ON THE ANTICIPATED LAG OF AUTOMATED
INTENSITY ESTIMATES AS AN EYE FEATURE STRUGGLES TO FORM. AGENCY
DVORAK ESTIMATES REMAIN LOWER AT T4.5 WHILE CIMSS ADT AND DEEP
MICRONET (DMN) INDICATE 82-83KTS.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   KNES: T4.5 - 77 KTS
   APRF: T4.5 - 77 KTS
   CIMSS SATCON: 68 KTS AT 120511Z
   CIMSS ADT: 82 KTS AT 120530Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: HIGHLY FAVORABLE
   VWS: 10-15 KTS
   SST: 30-31 CELSIUS
   OUTFLOW: STRONG POLEWARD
   OTHER FACTORS: ONSET OF RAPID INTENSIFICATION (RI) IS HIGHLY
LIKELY

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   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 (ILSA) IS FORECAST TO BEGIN ROUNDING
THE STR AXIS OVER THE NEXT 24 HOURS. DURING THAT TIME THE SYSTEM
WILL BEGIN TO TRACK SOUTH-SOUTHWESTWARD AND EVENTUALLY SOUTHWARD
ALL THE WHILE CONTINUING TO INTENSIFY. BY TAU 24, WARM SSTS
(30-31C), HIGH OHC VALUES, LOW VERTICAL WIND SHEAR AND STRONG
OUTFLOW ALOFT WILL MORE THAN COMPENSATE FOR THE DRY AIR FIGHTING TO
ENTRAIN THE SYSTEM. AFTER TAU 24, TC ILSA WILL BE TRACKING
GENERALLY SOUTHEASTWARD AND IS FORECAST TO REACH ITS PEAK INTENSITY
NEAR 130KTS. BY TAU 36, AS THE SYSTEM APPROACHES THE COAST OF
AUSTRALIA INTENSITIES WILL BEGIN TO FALL. AFTER TAU 36, 18S WILL
PUSH INLAND AND QUICKLY WEAKEN, EVENTUALLY DISSIPATING NEAR TAU 72.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT THAT 18S
WILL ROUND THE STR AXIS AND MAKE LANDFALL OVER THE RELATIVELY FLAT
TERRAIN OF EIGHTY MILE BEACH AND PROCEED INLAND UNTIL DISSIPATION.
DUE TO THE 70NM SPREAD IN SOLUTIONS AT LANDFALL THE JTWC FORECAST
TRACK IS PLACED CLOSE TO THE MULTI-MODEL CONSENSUS WITH HIGH
CONFIDENCE. RELIABLE MODEL INTENSITY GUIDANCE IS IN FAIR AGREEMENT
REFLECTING A CONTINUING SPREAD IN MODEL PEAK INTENSITY OUTPUT WITH
RAPID INTENSIFICATION (RI) AIDS AND OCEAN COUPLED MODELS (HWRF,
COAMPS-TC) INDICATING 120-125KTS WHILE DECAY-SHIPS REMAINS LOWER AT
100-105KTS. DUE TO THE LARGE IMPACT OHC AND SST VALUES ARE PLAYING
IN THE SYSTEMS DEVELOPMENT, THE JTWC INTENSITY FORECAST IS PLACED
AMONGST THE MORE AGGRESSIVE MEMBERS WITH MEDIUM CONFIDENCE.

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