WDXS32 PGTW 130300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 18S (EIGHTEEN) WARNING 
NR 008//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 14.5S 110.2E
   INITIAL INTENSITY: 35 KTS
   GEOGRAPHIC REFERENCE: 518 NM NORTH-NORTHWEST OF LEARMONTH,
AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 13 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A HIGHLY
IRREGULAR TROPICAL CYCLONE, WITH TWO DISTINCT LOWER-LEVEL
CIRCULATION CENTERS (LLCC), ONE TO THE NORTHWEST AND TRAVELLING
EASTWARD FASTER THAN THE SECOND CIRCULATION TO THE SOUTHEAST WHICH
APPEARS TO HAVE BECOME STATIONARY. THE TWO CENTERS ARE CURRENTLY
ASSESSED AS UNDERGOING A FUJIWHARA INTERACTION. STRONG 30KT
VERTICAL WIND SHEAR (VWS) FROM THE EAST IS BLOWING THE DEEP LAYER
CONVECTION COMPLETELY OFF OF THE VORTICES LEAVING BOTH CIRCULATIONS
FULLY EXPOSED, DESPITE A FAVORABLY MOIST ENVIRONMENT AND WARM SEA
SURFACE TEMPERATURES (SST). THE POSITION WAS ASSESSED WITH MEDIUM
CONFIDENCE GIVEN THAT THE POSITION WAS PLACED IN THE CENTROID
BETWEEN THE TWO CIRCULATIONS DEFINED ABOVE. THE INTENSITY WAS
ASSESSED WITH MEDIUM CONFIDENCE, AT A GENEROUS 35KTS, BASED ON AN
121800Z AMSR2 WINDSPEED PRODUCT SHOWING A BAND OF ELEVATED WIND
SPEEDS NORTH OF THE CIRCULATION. SUBJECTIVE AND OBJECTIVE INTENSITY
ESTIMATES ARE FOR THE MOST PART MUCH LOWER THAN THE AMSR2
MEASUREMENT.

INITIAL WIND RADII BASIS: OTHER (AMSR2 WINDSPEED PRODUCT). 

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: T2.0 - 30 KTS
   APRF: T1.5 - 25 KTS
   CIMSS ADT: 32 KTS AT 120030Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: WEAK WESTWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

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 TRACKING
EAST-SOUTHEAST ON THE SOUTHERN PERIPHERY OF AN NER TO THE NORTH FOR
THE NEXT 36 HOURS. INTERACTION WITH A SUBTROPICAL RIDGE (STR) OVER
THE CONTINENT OF AUSTRALIA IS EXPECTED TO SLOW THE SYSTEM AND
REDIRECT THE CYCLONE TO THE SOUTHWEST AT APPROXIMATELY TAU 72 AND
CONTINUING ON THAT TRACK THROUGH THE END OF THE FORECAST PERIOD.
THE FORECAST TRACK REMAINS UNCERTAIN, ESPECIALLY AFTER TAU 72, DUE
TO MODERATE DISAGREEMENT IN HOW STRONGLY THE STR WILL INFLUENCE THE
SYSTEM AND WHETHER IT WILL HAVE A NORTH-SOUTH ALIGNMENT FORCING THE
SYSTEM TO TRACK FARTHER SOUTH OR WILL HAVE AN EAST-WEST ALIGNMENT
ALLOWING THE STORM TO TRACK FARTHER EAST AND APPROACH THE
NORTHWESTERN COAST OF AUSTRALIA. IN THE NEAR-TERM, THE LACK OF AN
ORGANIZED, SINGULAR VORTEX, COMBINED WITH THE STRONG EASTERLY
SHEAR, WILL RESULT IN LITTLE TO NO INTENSIFICATION THROUGH TAU 24.
THE LATEST SHIPS OUTPUT CONTINUES TO INSIST THAT SHEAR WILL
DECREASE AFTER TAU 36, WHICH WILL ALLOW THE VORTEX TO FINALLY
CONSOLIDATE AND THE SYSTEM TO STEADILY INCREASE IN INTENSITY TO A
FORECASTED PEAK OF 80 KNOTS BY THE END OF THE FORECAST PERIOD. 

MODEL DISCUSSION: THE JTWC CONSENSUS TRACK GUIDANCE HAS OPENED OVER
THE LAST SIX HOURS TO A CROSS-TRACK ERROR OF 550NM BY TAU 120,
BANDED BY GALWEM TO THE WEST AND GFS TO THE EAST. GFS ANTICIPATES
THE SYSTEM WILL CONTINUE NEARLY DUE EAST BEFORE SHARPLY TURNING TO
THE SOUTHWEST AT TAU 72. ECMWF AND UKMET BOTH INITIALLY TRACK TO
THE EAST-SOUTHEAST, AND SLOWLY CURVE TO THE SOUTHWEST BETWEEN TAU
48 AND TAU 72. THE LARGE SPREAD IN THE DETERMINISTIC AND ENSEMBLE
GUIDANCE RESULTS IN LOW CONFIDENCE IN THE JTWC FORECAST, WHICH
CONFORMS CLOSELY TO THE ECMWF AND THE CONSENSUS MEAN. INTENSITY
GUIDANCE IS IN GOOD AGREEMENT IN TERMS OF THE GRADUAL INCREASE TO
80KTS BY TAU 120, HOWEVER BOTH COAMPS-TC (GFS-BASED) AND COAMPS-TC
(NAVGEM-BASED) HAVE SIGNIFICANTLY HIGHER PEAKS UP TO 100KTS.
ADDITIONALLY, THE COAMPS-TC ENSEMBLE INTENSITY PROBABILITY PRODUCT
SHOWS INCREASING CHANCES OF RAPID INTENSIFICATION AFTER TAU 96 (NOW
UP TO 40 PERCENT PROBABILITY), WHILE THE SAME PRODUCT BASED ON GEFS
SHOWS A LOW, BUT INCREASING CHANCE AS WELL. AS A RESULT, THE CHANCE
OF A PERIOD OF RI AT THE END OF THE FORECAST PERIOD CANNOT BE RULED
OUT. 

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