WDPS31 PGTW 211500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 31P (THIRTYONE) 
WARNING NR 014//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 11.6S 136.6E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 339 NM EAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 11 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A VERY
WEAK, AND FULLY EXPOSED LOW LEVEL CIRCULATION CENTER PASSING OVER
THE SOUTHERN PORTION OF THE WESSEL ISLANDS. THE VIGOROUS CONVECTION
NOTED SIX HOURS AGO RAPIDLY AND COMPLETELY COLLAPSED AROUND 0800Z,
REVEALING A SMALL LOW LEVEL CIRCULATION CENTER (LLCC). THE MOST
RECENT SATELLITE DATA SHOWS CONVECTION FLARING UP ONCE MORE ALONG
THE EASTERN FLANK OF THE CIRCULATION BUT IT REMAINS DISORGANIZED
AND IS LIKELY TO BE UNABLE TO PERSIST OR REORGANIZE IN THE SHORT
TERM. A 210930Z SSMIS COLOR-ENHANCED 91GHZ MICROWAVE IMAGE REVEALED
A WEAK LLCC JUST NORTH OF GOVE AIRPORT, WITH ONLY FRAGMENTARY,
WEAK LOW-LEVEL BANDING FEATURES. THE VORTEX IS SO SHALLOW THAT IT
IS BARELY EVIDENT ON THE GOVE RADAR. THE INITIAL POSITION IS
ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE MOSTLY EXPOSED LLCC IN
THE ANIMATED EIR, THE GOVE RADAR AS WELL AS SURFACE OBSERVATION
DATA FROM GOVE AIRPORT AND CAPE WESSEL. THE INITIAL INTENSITY IS
ASSESSED WITH LOW CONFIDENCE, AND IN FACT THE ACTUAL INTENSITY MAY
BE A BIT LOWER, AS THE HIGHEST WINDS HAVE LONG BEEN LOCATED IN THE
SOUTHERN PORTION OF THE CIRCULATION, WHICH IS NOW OVER LAND, WITH
FRICTIONAL EFFECTS LIKELY LOWER THOSE MAXIMUM WINDS BELOW 30 KNOTS.
THE ENVIRONMENT IS GENERALLY FAVORABLE, WITH LOW VWS, WARM SSTS AND
DECENT OUTFLOW ALOFT BUT THE CONTINUE INTRUSION OF DRY AIR IN THE
LOW LEVELS AND INTERACTION WITH TERRAIN ARE DISRUPTING THE SYSTEM.

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

CURRENT STEERING MECHANISM: NORTHEASTERN PERIPHERY OF A LOW- TO
MID-LEVEL RIDGE CENTERED OVER NORTHERN AUSTRALIA. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T1.5 - 25 KTS
   ADRM: T2.0 - 30 KTS
   CIMSS ADT: 47 KTS AT 211130Z
   CIMSS AIDT: 38 KTS AT 211130Z
   CIMSS D-MINT: 28 KTS AT 210930Z
   CIMSS D-PRINT: 28 KTS AT 211130Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: LAND INTERACTION AND DRY AIR INTRUSION. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: MEDIUM
   INITIAL INTENSITY: LOW
   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: TC 31P IS MOVING NORTHWESTWARD AT A STEADY
SPEED OF AROUND 10 KNOTS, ALONG THE NORTHERN SIDE OF A LOW- TO
MID-LEVEL RIDGE SITUATED OVER NORTHERN AUSTRALIA. NO SIGNIFICANT
CHANGE IS EXPECTED IN THE OVERALL STEERING PATTERN THROUGH THE
FORECAST PERIOD, OTHER THAN A GENERAL WEAKENING OF THE STEERING
GRADIENT AFTER TAU 24 WHICH WILL CAUSE TC 31P TO SLOW DOWN SLIGHTLY
TOWARDS THE END OF THE FORECAST. THE SYSTEM IS CURRENTLY PASSING
OVER GULUWURU AND RARAGALA ISLANDS AND WILL SOON EMERGE INTO THE
ARAFURA SEA. THE NORTHWESTWARD TRACK MEANS THE SYSTEM WILL MOVE
FURTHER AWAY FROM LAND AS TIMES GOES ON. SHEAR IS FORECAST TO
STEADILY DECREASE OVER THE NEXT 24 TO 36 HOURS, AND AS THE SYSTEM
MOVES FURTHER AWAY FROM LAND AND FRICTIONAL EFFECTS LESSEN, BOTH
THE HAFS-A AND GFS INDICATE A SHORT PERIOD OF VORTEX ALIGNMENT AND
INTENSIFICATION. HOWEVER, AS THE SYSTEM MOVES FURTHER EQUATORWARD,
IT MOVES INTO A MORE HOSTILE SHEAR REGIME AND WILL RAPIDLY WEAKEN
BELOW WARNING THRESHOLD BY TAU 48. HOWEVER, THERE IS A POSSIBILITY
OF REGENERATION IF THE SYSTEM LOOPS BACK TO THE SOUTH AS SEVERAL OF
THE MODELS SUGGEST. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD AGREEMENT
THROUGH TAU 48, WITH ALL CONSENSUS MEMBERS EXCEPT THE NAVGEM,
CONFINED TO A VERY TIGHT ENVELOPE OF JUST 50NM. ALONG-TRACK
UNCERTAINTY REMAINS MUCH HIGHER, WITH THE ECMWF AND THE ECENS MEAN
OUTPACING THE OTHER MODELS, PUSHING OUT AHEAD OF THE PACK BY ABOUT
100NM BY TAU 48. THE JTWC FORECAST IS PLACED ON THE NORTHERN EDGE
OF THE GUIDANCE ENVELOPE, CLOSE TO THE CONSENSUS MEAN, WITH HIGH
CONFIDENCE. INTENSITY GUIDANCE REMAINS MIXED, THOUGH ALL MODELS
AGREE ON THE SYSTEM INTENSIFYING AROUND TAU 24, PEAKING AROUND TAU
36 THEN WEAKENING AGAIN. THE MAIN EXCEPTION IS THE SHIPS-GFS WHICH
SHOWS THE SYSTEM STEADILY INTENSIFYING THROUGH THE FORECAST PERIOD.
THE JTWC FORECAST IS PLACED AMONGST THE TIGHTEST PACKING OF MODELS
AND THE CONSENSUS MEAN, WITH MEDIUM CONFIDENCE. 

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