WDPS31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 03P (JASPER) WARNING 
NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.4S 155.8E
   INITIAL INTENSITY: 90 KTS
   GEOGRAPHIC REFERENCE: 583 NM EAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 04 KTS
   SIGNIFICANT WAVE HEIGHT: 32 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT TC 03P
(JASPER) HAD UNDERGONE A PERIOD OF SIGNIFICANT DEGRADATION. THE
DEEP DISORGANIZED CONVECTION SEEN EARLIER HAS DISSIPATED AND CLOUD
TOP TEMPERATURES OF THE REMAINING CONVECTIVE ACTIVITY HAS WARMED
SIGNIFICANTLY AND BECOME EVEN MORE DISORGANIZED OVER THE PAST SIX
HOURS. THE LOW LEVEL CIRCULATION CENTER (LLCC) REMAINS OBSCURED,
BUT A 082310Z ASCAT-B BULLSEYE REVEALS THAT THE LLCC REMAINS
WELL-DEFINED BUT DISPLACED TO THE NORTH-NORTHWEST OF THE BROAD
UPPER-LEVEL ROTATION DUE TO STRONG NORTHWESTERLY SHEAR. THE INITIAL
POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN AMBIGUITY
ANALYSIS OF THE AFOREMENTIONED ASCAT PASS. THE INITIAL INTENSITY OF
90 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A ROUGH
AVERAGE OF THE SUBJECTIVE AND OBJECTIVE FIX ESTIMATES AND
EXTRAPOLATION OF AN EARLIER 081913Z SENTINEL-1A SAR PASS WHICH
REVEALED MAXIMUM WINDS BETWEEN 96-103 KNOTS. THE SYSTEM IS CLEARLY
BEING IMPACTED HARSHLY BY THE SUSTAINED 25-30 KNOT NORTHWESTERLY
SHEAR, AND AN INFLUX OF VERY DRY MID- TO UPPER-LEVEL AIR MOVING IN
OVER TOP OF THE SYSTEM FROM THE WEST. WHILE SSTS REMAIN WARM AND
UPPER-LEVEL OUTFLOW REMAINS MODERATELY STRONG TO THE EAST AND
POLEWARD, THE NEGATIVE EFFECTS OF THE SHEAR AND DRY AIR ARE
OVERWHELMING THE POSITIVE EFFECTS, GENERATING A MARGINALLY
UNFAVORABLE ASSESSMENT OF THE ENVIRONMENT. THE SYSTEM HAS NOW
STARTED TO TRACK TOWARDS THE SOUTHWEST, WITH THE SUBTROPICAL RIDGE
(STR) TO THE SOUTH TAKING OVER THE DOMINANT STEERING ROLE.

INITIAL WIND RADII BASIS: SCATTEROMETER AND SAR DATA 

CURRENT STEERING MECHANISM: NORTHERN PERIPHERY OF A STR CENTERED TO
THE SOUTH. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.0 - 90 KTS
   KNES: T5.5 - 102 KTS
   ABRF: T5.5 - 102 KTS
   CIMSS ADT: 92 KTS AT 082330Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 30+ KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: MID-LEVEL DRY AIR. 

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: NOW THAT THE STR TO THE SOUTH HAS ASSUMED THE
DOMINANT STEERING ROLE, TC 03P IS FORECAST TO TRACE A GRACEFUL
WEST-SOUTHWEST TO WEST ARC OVER THE NEXT 48 HOURS, MOVING ALONG THE
NORTHERN SIDE OF THE STR TO THE SOUTH. THE SYSTEM IS EXPECTED TO
PASS THE OUTERMOST LINE OF REEF STATIONS, PASSING BETWEEN WILLIS
ISLAND AND LIHOU REEF AROUND TAU 48. THE RIDGE IS EXPECTED TO PUSH
NORTHWARD SHORTLY AFTER TAU 48, WHICH WILL PUSH TC 03P ONTO A MORE
WEST-NORTHWEST TRACK THROUGH TAU 72, BEFORE FLATTENING OUT ONCE
MORE BY THE END OF THE FORECAST. LANDFALL IS EXPECTED ALONG THE
EASTERN COAST OF AUSTRALIA, NORTH OF CAIRNS, JUST AFTER TAU 96. THE
SYSTEM IS CLEARLY WEAKENING FAIRLY QUICKLY, AND THE PACE OF
WEAKENING IS ANTICIPATED TO ACCELERATE OVER THE NEXT 24 HOURS AS
THE HIGH SHEAR VALUES PERSIST AND DRY AIR CONTINUES TO ENGULF AND
SMOTHER THE SYSTEM. THE SYSTEM IS FORECAST TO BOTTOM OUT AT 55
KNOTS AT TAU 72, THOUGH A SLIGHTLY LOWER INTENSITY AT THE BOTTOM IS
POSSIBLE. GLOBAL MODEL FIELDS SHOW A SHARP DECREASE IN SHEAR JUST
AFTER TAU 72, ACCOMPANIED BY A DRAMATIC INCREASE IN DEEP-LAYER
MOISTURE, WHICH WILL ALLOW TC 03P TO REINTENSIFY AS IT MOVES OVER
THE WARM, SHALLOW WATERS OF THE GREAT BARRIER REEF. THE CURRENT
FORECAST CALLS FOR A PEAK OF 70 KNOTS AT TAU 96, BUT IT IS POSSIBLE
THAT A SLIGHTLY HIGHER PEAK COULD OCCUR IMMEDIATELY PRIOR TO OR
COINCIDENT WITH LANDFALL. ONCE ASHORE, THE SYSTEM WILL RAPIDLY
WEAKEN DUE TO FRICTIONAL EFFECTS OVER LAND.  

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH THE ENTIRE FORECAST PERIOD, WITH THE ENVELOPE SHRINKING
SINCE THE PREVIOUS MODEL RUN. CROSS-TRACK SPREAD IS NOW 125NM AT
TAU 72 AND 210NM AT TAU 120, IF THE NAVGEM IS DISCOUNTED AS A
SIGNIFICANT OUTLIER FAR TO THE SOUTH. IN LIGHT OF THE RECENT SHIFT
IN THE TRACK HOWEVER, THE JTWC FORECAST LIES ON THE NORTHERN EDGE
OF THE TRACK ENVELOPE. CONFIDENCE IS HIGH THROUGH TAU 72, AND
MEDIUM THEREAFTER AS THE SYSTEM APPROACHES LAND. INTENSITY GUIDANCE
IS ALSO IN GOOD AGREEMENT, WITH ALL MODELS SHOWING STEADY WEAKENING
THROUGH TAU 72 FOLLOWED BY A REINTENSIFICATION PERIOD PRIOR TO
LANDFALL. THE BOTTOM OF THE INTENSITY RANGES BETWEEN 45-60 KNOTS,
WHILE THE SECOND PEAK RANGES FROM 55-70 KNOTS. THE JTWC FORECAST
LIES CLOSE TO THE CONSENSUS MEAN TO TAU 72, THEN PUSHES SLIGHTLY
HIGHER THAN THE MEAN AT TAU 96, WITH MEDIUM CONFIDENCE. 

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