WDXS32 PGTW 162100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING 
NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 16.7S 113.8E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 336 NM NORTH OF LEARMONTH, AUSTRALIA
   MOVEMENT PAST 6 HOURS: NORTH-NORTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 14 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL
CYCLONE (TC) 18S WITH A SUBSTANTIALLY OBSCURED LOW LEVEL
CIRCULATION CENTER (LLCC) UNDER FLARING CONVECTION. LOW-LEVEL
CLOUDS BAND INTO THE MOIST CENTER FROM THE WEST AND EAST AS DRY AIR
ENTRAINS FROM THE NORTHWEST. THE ANIMATED EIR SUGGESTS THAT SYSTEM
HAS BECOME MORE VERTICALLY ALIGNED OVER THE LAST SIX HOURS AS THE
LLCC HAS TUCKED UNDER THE EASTERN EDGE OF THE CONVECTION. ON THE
UPPER-LEVELS, WEAK OUTFLOW DRIFTS WESTWARD AND POLEWARD. AS THE
SYSTEM HAS REMAINED QUASI-STATIONARY (QS) WHILE IN A COMPETING
STEERING ENVIRONMENT OVER THE LAST COUPLE OF DAYS, WEAK OCEANIC
UPWELLING HAS COOLED THE SEA SURFACE TEMPERATURES (SST) THOUGH SSTS
REMAIN FAVORABLE BETWEEN 28-29C. A TIGHT GRADIENT OF MODERATE
EASTERLY VERTICAL WIND SHEAR (VWS) REMAINS OVER THE SYSTEM. THE
INITIAL POSITION WAS DETERMINED WITH MEDIUM CONFIDENCE USING
ANIMATED EIR DEPICTING LOW-LEVEL TURNING, HOWEVER THE UPPER-LEVELS
OBSCURE THE MAJORITY OF THE LLCC. THE POSITION WAS FURTHER
SUPPORTED USING A 161745Z 91GHZ AMSR-2 MICROWAVE IMAGE SHOWING A
BROAD REGION OF LOW-LEVEL TURNING. THE INTENSITY WAS ASSESSED WITH
LOW CONFIDENCE BASED ON THE AGENCY AND OBJECTIVE FIXES LISTED
BELOW.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: A COMPETING STEERING ENVIRONMENT ON THE
LOW TO MID LEVELS BETWEEN A NEAR EQUATORIAL RIDGE (NER) TO THE
NORTH AND A WEAKENING SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   DEMS: T1.5 - 25 KTS
   APRF: T1.5 - 25 KTS
   CIMSS ADT: 45 KTS AT 161740Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK RADIAL

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   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 IS FORECAST TO REMAIN IN A QS STATE
OVER THE NEXT 36 HOURS, MEANDERING TO THE WEST INITIALLY THROUGH
THE FIRST TWELVE HOURS BEFORE TRACKING SOUTHWEST AS THE STR TO THE
SOUTHEAST WEAKENS. WHILE IN THE REGION OF WEAKNESS, IT IS POSSIBLE
THAT THERE MAY BE UNANTICIPATED DIRECTIONAL DRIFTING, EVEN LOOPING
OF THE TRACK. BETWEEN TAU 48 AND 72, ANOTHER STR TO THE SOUTHEAST
EXTENDING OVER WESTERN AUSTRALIA IS EXPECTED TO BUILD AND DRIVE TC
18S TO THE WEST, PICKING UP TO A TRACK SPEED OF 8KTS BY THE END OF
THE FORECAST PERIOD. THE SYSTEM IS FORECAST TO MEAGERLY INTENSIFY
TO 40KTS BY TAU 36 AND TO 45KTS BY TAU 72 DESPITE A DECREASE IN VWS
AND IMPROVING CONDITIONS FOR OUTFLOW PRIMARILY DUE TO A RELATIVE
DECREASE IN SST AND OCEAN HEAT CONTENT (OHC) AS THE SYSTEM REMAINS
IN THE AREA FOR THE FIRST 48 HOURS. ONCE TC 18S MOVES OUT OF THE
REGION, IT IS FORECAST TO INTENSIFY STEADILY TO 55KTS BY THE END OF
THE FORECAST PERIOD AS THE SYSTEM MOVES INTO AN ENVIRONMENT LOWER
VWS, MODERATELY IMPROVED OUTFLOW, BUT ALSO RELATIVELY LOW SSTS AND
OHC. 

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN BETTER
AGREEMENT THAT TC 18S WILL REMAIN QS OVER THE NEXT 48 HOURS BEFORE
TRANSITIONING WEST AS A STR OVER THE AUSTRALIAN CONTINENT BUILDS.
BOTH ECMWF AND THE ECMWF ENSEMBLE DRIFT THE SYSTEM TO THE NORTHWEST
AND TAKE AN EASTWARD LOOP BEFORE DIPPING SOUTHWEST CONTINUING ON
ITS WESTWARD TRACK BY TAU 72. EXCLUDING THE OUTLIER OF NAVGEM, THE
CROSS-TRACK ERROR IS 250NM BY TAU 120. THE JTWC INTENSIFY GUIDANCE
REMAINS SIGNIFICANTLY INCONGRUENT AS THE INTENSITY GUIDANCE HAS A
125KT SPREAD BY THE END OF THE FORECAST PERIOD. THE HWRF
INTERPOLATION FORECASTS A PEAK OF 150KTS, HWRF TRAILING BEHIND AT
110KTS BY TAU 120 WHILE COAMPS-TC FORECASTS THAT THE SYSTEM WILL
REMAIN STAGNANT AT 35KTS BY TAU 84. THE JTWC FORECAST WAS ASSESSED
WITH LOW CONFIDENCE, BALANCING THE IMPROVEMENT IN VORTEX STRUCTURE
AS VWS INCREASES BUT ALSO ACKNOWLEDGING THE LOW OHC SUPPORTING THE
CYCLONE.

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