WDPS31 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 31P (THIRTYONE)  
WARNING NR 004//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.4S 141.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 627 NM EAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: SOUTHEASTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED VISIBLE SATELLITE IMAGERY DEPICTS A PARTIALLY-EXPOSED LOW-
LEVEL CIRCULATION (LLCC), WITH FLARING DEEP CONVECTION OBSCURING THE 
LLCC. ANIMATED RADAR IMAGERY FROM THE WEIPA RADAR REVEALS WEAK, 
FRAGMENTED RAINBANDS WRAPPING INTO A BROAD LLCC, WHICH SUPPORTS THE 
INITIAL POSITION WITH MEDIUM CONFIDENCE. AN 182119Z SSMIS 91GHZ COLOR 
COMPOSITE MICROWAVE IMAGE DEPICTS LIMITED DEEP CONVECTIVE BANDING 
OVER THE WESTERN QUADRANT WITH EXTENSIVE SHALLOW BANDING OVER THE 
WESTERN SEMICIRCLE. SURFACE OBSERVATIONS FROM WEIPA AERO, 
APPROXIMATELY 27NM TO THE SOUTHEAST, INDICATE 15-20 KNOT EASTERLY 
SUSTAINED WINDS. ENVIRONMENTAL CONDITIONS ARE MARGINAL DUE TO LOW TO 
MODERATE VERTICAL WIND SHEAR (VWS) AND WEAK POLEWARD OUTFLOW. 
ADDITIONALLY, THE SYSTEM'S STRUCTURE IS SHALLOW, WITH THE UPPER-LEVEL 
CIRCULATION CENTER LOCATED SOUTHWEST OF THE LLCC. DUE TO THE MARGINAL 
ENVIRONMENT AND INTERACTION WITH CAPE YORK PENINSULA, THE SYSTEM HAS 
STRUGGLED TO CONSOLIDATE. THE INTENSITY REMAINS ASSESSED AT 30 KNOTS 
BASED ON PERSISTENCE AND A BLEND OF SUBJECTIVE AND OBJECTIVE 
INTENSITY ESTIMATES RANGING FROM 24 TO 35 KNOTS.

INITIAL WIND RADII BASIS: NOT APPLICABLE (THERE ARE NO INITIAL WIND
RADII).

CURRENT STEERING MECHANISM: COMPETING STEERING ENVIRONMENT, WITH A
NEAR-EQUATORIAL RIDGE (NER) TO THE NORTH AND LOW- TO MID-LEVEL
SUBTROPICAL RIDGE (STR) EXTENDING TO THE SOUTHEAST AND WEST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   ADRM: T2.5 - 35 KTS
   CIMSS SATCON: 35 KTS AT 182121Z
   CIMSS ADT: 32 KTS AT 182330Z
   CIMSS AIDT: 28 KTS AT 182330Z
   CIMSS D-MINT: 24 KTS AT 182121Z
   CIMSS D-PRINT: 27 KTS AT 190110Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 15-20 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: NOT APPLICABLE

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 31P WILL TRACK SLOWLY
AND PERHAPS ERRATICALLY THROUGH TAU 12 BUT SHOULD BEGIN TO TURN
WESTWARD BY TAU 24 AS A STR BUILDS TO THE SOUTH. THIS STR WILL DRIVE 
THE SYSTEM WEST-NORTHWESTWARD THROUGH THE REMAINDER OF THE FORECAST 
PERIOD. TC 31P SHOULD BEGIN TO RE-INTENSIFY AFTER TAU 12 AS THE 
VORTEX BECOMES BETTER ALIGNED THROUGH THE MID-LEVELS AND THE 
ENVIRONMENT MOISTENS. PEAK INTENSITY COULD POSSIBLY PEAK SLIGHTLY 
HIGHER THAN 40 KNOTS AS THE SYSTEM TRAVERSES THE GULF OF CARPENTARIA. 
HOWEVER, GRADUAL WEAKENING IS ANTICIPATED AFTER TAU 72 AS THE SYSTEM 
SKIRTS THE NORTHERN COAST OF AUSTRALIA AND TRACKS EQUATORWARD.     

MODEL DISCUSSION: THE BULK OF THE DETERMINISTIC GUIDANCE SUPPORTS
THE JTWC TRACK FORECAST WITH MEDIUM OVERALL CONFIDENCE, WITH NAVGEM 
AND UKMET THE PRIMARY OUTLIERS. THE 181800Z ECMWF AND GFS ENSEMBLES
(EPS, GEFS) SHOW A SIMILAR SPREAD OF SOLUTIONS, WITH THE LARGE 
MAJORITY OF SOLUTIONS IN THE 20-40 KNOT INTENSITY RANGE. 
ADDITIONALLY, THE BULK OF THE SOLUTIONS SUPPORT A TRACK NORTHEAST OF 
DARWIN AND NORTH OF THE NORTHERN COAST OF AUSTRALIA AFTER TAU 72. 
RELIABLE INTENSITY GUIDANCE INDICATES A SLOW INTENSIFICATION RATE, 
WITH COAMPS-TC (GFS) PEAKING AT 40 KNOTS AND HAFS-A PEAKING AT 48 
KNOTS.     

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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