WDPS31 PGTW 201500 AMD
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 31P (THIRTYONE) 
WARNING NR 010A AMENDED//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 12.6S 140.2E
   INITIAL INTENSITY: 30 KTS
   GEOGRAPHIC REFERENCE: 545 NM EAST OF DARWIN, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WESTWARD AT 07 KTS
   SIGNIFICANT WAVE HEIGHT: 10 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS TC 31P
STILL STRUGGLING TO ORGANIZE. CONVECTIVE ACTIVITY HAS INCREASED
SIGNIFICANTLY OVER THE PAST SIX HOURS, HOWEVER THE CONVECTION
REMAINS DISORGANIZED AND LOOKS TO HAVE ALREADY STARTED TO WEAKEN
JUST IN THE LAST HOUR. THE LOW LEVEL CIRCULATION CENTER (LLCC) IS
FULLY OBSCURED AND THE LACK OF RECENT HIGH-RESOLUTION MICROWAVE
IMAGERY PRECLUDES A HIGH CONFIDENCE ASSESSMENT OF THE UNDERLYING
STRUCTURE. HOWEVER, LATE RECEIPT OF A 201235Z ASCAT-C BULLSEYE PASS
REVEALS THAT THE LLCC IS POSITIONED IN THE NORTHWESTERN PORTION OF
THE CONVECTIVE MASS, AND FAIRLY FAR REMOVED FROM THE CENTER OF THE
DEEPEST CONVECTIVE ACTIVITY. THE INITIAL POSITION IS UPDATED TO BE
ASSESSED WITH HIGH CONFIDENCE AND THE FORECAST HAS BEEN AMENDED TO
REFLECT THIS CHANGE. THE INITIAL INTENSITY IS ALSO ASSESSED WITH
HIGH CONFIDENCE, ON THE LOWER END OF THE AVAILABLE OBJECTIVE AND
SUBJECTIVE ESTIMATES NOTED ABOVE, AND CONFIRMED BY THE ASCAT PASS
WHICH SHOWS ONLY A VERY SMALL PATCH OF 30 KNOT WINDS TO THE SOUTH
OF THE LLCC. THE ENVIRONMENT REMAINS GENERALLY FAVORABLE FOR
DEVELOPMENT, WITH WARM SSTS, HIGH OHC AND GOOD POLEWARD OUTFLOW.
SHEAR HAS PICKED UP A NOTCH, TO 14 KNOTS, BASED ON THE MOST RECENT
CIMSS ESTIMATE BUT STILL REMAINS IN THE LOW RANGE. VORTEX TILT AND
ASYMMETRIES, ALONG WITH THE DRY MID-LEVEL AIR TO THE NORTH, REMAIN
THE PRIMARY HINDRANCES TO DEVELOPMENT AT THE MOMENT.

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

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   KNES: T2.0 - 30 KTS
   ADRM: T2.5 - 35 KTS
   CIMSS SATCON: 40 KTS AT 201210Z
   CIMSS ADT: 41 KTS AT 201140Z
   CIMSS AIDT: 36 KTS AT 201140Z
   CIMSS D-MINT: 28 KTS AT 200832Z
   CIMSS D-PRINT: 29 KTS AT 201240Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 10-15 KTS
   SST: 29-30 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIR TO THE NORTH ALONG WITH VORTEX
ASYMMETRIES AND VERTICAL TILT. 

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: BASED ON THE UPDATED POSITIONING DATA, TC 31P
HAS DEFINITELY STARTED ITS RUN TOWARDS THE OPEN WATERS OF THE GULF
OF CARPENTARIA, PICKING UP SPEED TO ABOUT SEVEN KNOTS AS THE
BUILDING LOW- TO MID-LEVEL RIDGE TO THE SOUTH TAKES OVER AS THE
PRIMARY STEERING MECHANISM. THE OVERALL STEERING FLOW IS EXPECTED
TO STRENGTHEN OVER THE NEXT DAY AS THE LOW- TO MID-LEVEL FLOW
ALIGNS WITH THE DEEP-LAYER FLOW, ALONG THE NORTHEASTERN SIDE OF A
DEVELOPING DEEP-LAYER RIDGE TO THE SOUTHWEST. THE END RESULT WILL
BE AN INCREASE IN FORWARD SPEED ALONG A STEADY NORTHWESTWARD TRACK
THROUGH MAJORITY OF THE FORECAST PERIOD. THE SYSTEM SHOULD PASS JUST
NORTH OF GOVE AIRPORT AROUND TAU 24, THEN INTO THE CENTRAL ARAFURA
SEA, ULTIMATELY PASSING INTO THE BANDA SEA EAST OF BABAR ISLAND. IN
TERMS OF INTENSITY, THE SYSTEM IS STILL STRUGGLING AGAINST SOME
LEVEL OF INCREASED SHEAR, THOUGH IN THE WRONG DIRECTION. THE
DEEP-LAYER SHEAR VECTOR IS NORTHEASTERLY, BUT THE VORTEX IS
ACTUALLY TILTED IN THE OPPOSITE DIRECTION, ALONG THE MID-LEVEL
SHEAR VECTOR, WHICH IS FROM THE WEST-NORTHWEST. REGARDLESS, THE
VORTEX IS NOT ALIGNED VERTICALLY, WHICH IS HINDERING DEVELOPMENT
FOR THE TIME BEING. MODELS SUGGEST A WEAKENING OF SHEAR GOING
FORWARD, WHICH SHOULD ALLOW FOR A BRIEF INTENSIFICATION PHASE OVER
THE NEXT 24 HOURS. THE CLOSE APPROACH TO CAPE WILBERFORCE WILL
DISRUPT THE SYSTEM RIGHT AS IT IS EXPECTED TO PEAK, PUTTING A CAP
ON FURTHER DEVELOPMENT. SLOWLY INCREASING SHEAR AND DRY AIR
INTRUSION WILL OFFSET OTHERWISE FAVORABLE SSTS AND OUTFLOW AFTER
TAU 36, KEEPING THE SYSTEM BASICALLY IN A STEADY-STATE THROUGH TAU
72. AS THE SYSTEM MOVES INTO THE BANDA SEA, SHEAR PICKS UP RAPIDLY,
LEADING TO DISSIPATION BY TAU 96. 

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN VERY GOOD
AGREEMENT THROUGH THE FORECAST PERIOD, WITH THE SOLE EXCEPTION OF
NAVGEM, WHICH TAKES A SHARP LEFT TURN ENDING UP NEAR DARWIN AT TAU
96. THE REMAINDER OF THE GUIDANCE PACKAGE IS CONFINED TO A NARROW
55NM ENVELOPE THAT POINTS RIGHT AT THE CHANNEL BETWEEN BABAR AND
SELARU ISLANDS. THE JTWC FORECAST LIES ON THE NORTHERN EDGE OF THAT
ENVELOPE, CLOSE TO THE CONSENSUS MEAN, WITH HIGH CONFIDENCE.
INTENSITY GUIDANCE IS MIXED, WITH THE HAFS-A AND MESOSCALE GFS
INDICATING ONLY WEAK DEVELOPMENT THROUGH TAU 12 FOLLOWED BY GENERAL
WEAKENING THEREAFTER. MEANWHILE THE COAMPS-TC AND ESPECIALLY THE
SHIPS GUIDANCE (BOTH NAVGEM AND GFS) SHOW INTENSIFICATION UP TO 55
KNOTS BY TAU 60. THE JTWC FORECAST REMAINS CONSISTENT WITH THE
PREVIOUS FORECASTS, AND TRACES THE COAMPS-TC AND CONSENSUS MEAN
WITH MEDIUM CONFIDENCE. 

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   TRACK 72-120 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM
   INTENSITY 72-120 HR: MEDIUM

4. JUSTIFICATION FOR AMENDMENT: UPDATED THE INITIAL POSITION BASED
ON LATE RECEIPT OF SCATTEROMETER DATA.//
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