WDPS31 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 31P (THIRTYONE) 
WARNING NR 007//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.5S 141.0E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 592 NM EAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 01 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TWO 
DISCRETE AREAS OF LINEAR DEEP CONVECTION PERSISTING OVER THE WESTERN 
AND EASTERN SEMICIRCLES. DUE TO THE WEAK NATURE OF THE SYSTEM, THE 
EIR IMAGERY IS USELESS FOR POSITIONING. FORTUNATELY, ANIMATED RADAR 
IMAGERY SHOWS MODERATE RAINBANDS WRAPPING TIGHTLY INTO A WELL-DEFINED 
LOW-LEVEL CIRCULATION CENTER (LLCC), WHICH SUPPORTS THE INITIAL 
POSITION WITH HIGH CONFIDENCE. A 191809Z SSMIS 91GHZ MICROWAVE IMAGE 
REVEALS SHALLOW BANDING WRAPPING INTO A WEAK LLCC, WITH ISOLATED 
CONVECTIVE BURSTS AROUND THE PERIPHERY OF THE LLCC. VERTICAL WIND 
SHEAR HAS DECREASED TO 10-15 KNOTS; HOWEVER, OVERALL ENVIRONMENTAL 
CONDITIONS REMAIN MARGINAL, WITH WEAK OUTFLOW, INTERACTION WITH LAND 
AND POSSIBLY DRY AIR ENTRAINMENT FROM CAPE YORK PENINSULA. 
ADDITIONALLY, THE SYSTEM IS SLIGHTLY TILTED, WITH THE UPPER-LEVEL 
CIRCULATION DISPLACED TO THE SOUTH. THE INITIAL INTENSITY OF 30 KTS 
IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE PGTW AND ADRM DVORAK 
ESTIMATES. CIMSS OBJECTIVE INTENSITY ESTIMATES RANGE FROM 27 TO 39 
KNOTS.

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

CURRENT STEERING MECHANISM: WEAK SUBTROPICAL RIDGE (STR) BUILDING
TO THE SOUTHWEST 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.0 - 30 KTS
   KNES: T1.5 - 25 KTS
   ADRM: T2.0 - 30 KTS
   CIMSS SATCON: 39 KTS AT 191402Z
   CIMSS ADT: 39 KTS AT 191730Z
   CIMSS AIDT: 33 KTS AT 191730Z
   CIMSS D-PRINT: 25 KTS AT 191800Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: WEAK POLEWARD

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: HIGH
   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 IS LOCATED IN A WEAK
STEERING ENVIRONMENT, WITH A STR BUILDING TO THE SOUTHWEST. 
THEREFORE, TRACK MOTION HAS BEEN VERY SLOW OVER THE PAST 12 HOURS. 
HOWEVER, THE STR IS FORECAST TO STRENGTHEN WITHIN THE NEXT 06-12 
HOURS, WHICH WILL ACCELERATE THE SYSTEM WESTWARD. TC 31P SHOULD BEGIN 
TO RE-INTENSIFY AFTER TAU 24 AS THE SYSTEM TRACKS AWAY FROM THE CAPE 
YORK PENINSULA, WITH A MODEST INCREASE IN THE PEAK INTENSITY TO 40 
KNOTS BY TAU 48. AFTER TAU 48, TC 31P WILL TRACK WEST-NORTHWESTWARD, 
WITH GRADUAL WEAKENING AND DISSIPATION ANTICIPATED BY TAU 96. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE HAS REMAINED IN FAIR
AGREEMENT, WITH THE BULK OF THE GUIDANCE SUPPORTING THE JTWC TRACK 
FORECAST. PROBABILISTIC GUIDANCE FROM THE 191200Z GEFS AND ECENS RUNS 
SHOWS A HIGH PROBABILITY OF THE SYSTEM TRACKING OVER WATER NORTH OF 
ARNHEM LAND. ALTHOUGH THE SYSTEM IS NOT EXPECTED TO BRING MAJOR 
IMPACTS TO THE DARWIN AREA, ENHANCED GRADIENT WINDS MAY OCCUR AS THE 
SYSTEM PASSES NORTH OF DARWIN IN THREE DAYS. THERE IS QUITE A BIT OF 
UNCERTAINTY IN THE JTWC INTENSITY FORECAST, WITH GUIDANCE RANGING 
FROM 30 TO 45 KNOTS. GFS IS ON THE LOW END OF THE GUIDANCE ENVELOPE 
AND NOW INDICATES SIGNIFICANT TILT TO THE VORTEX THROUGH THE NEXT TWO 
DAYS. HAFS-A AND COAMPS-TC (GFS) ARE MORE OPTIMISTIC, WITH PEAK 
INTENSITY VALUES OF 40-42 KNOTS FROM TAU 24-48.     

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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