WDPS31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL CYCLONE 03P (JASPER) WARNING 
NR 020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 15.9S 154.9E
   INITIAL INTENSITY: 60 KTS
   GEOGRAPHIC REFERENCE: 527 NM EAST OF CAIRNS, AUSTRALIA
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 03 KTS
   SIGNIFICANT WAVE HEIGHT: 30 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL CYCLONE (TC) 03P (JASPER) CONTINUES TO STEADILY ERODE AND
WEAKEN UNDER THE INFLUENCE OF PERSISTENT MODERATE WIND SHEAR AND
DRY AIR ENTRAINMENT. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY DEPICTS DISORGANIZED WEAK CONVECTIVE ACTIVITY SCATTERED
AROUND AN OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC). A
FORTUITOUS 091750Z GMI 36GHZ MICROWAVE IMAGE SHOWS THAT THE LLCC
REMAINS WELL-DEFINED, WITH LOW-LEVEL BANDING FEATURES WRAPPING INTO
A RELATIVELY LARGE LOW EMISSIVITY REGION, OUTLINING THE CENTER OF
THE CIRCULATION. WITH THE RECEIPT OF THE MICROWAVE IMAGERY, THERE
IS HIGH CONFIDENCE IN THE INITIAL POSITION. THE INITIAL INTENSITY
IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A BLEND OF AVAILABLE
SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES AS OUTLINED BELOW. THE
SYSTEM IS MOVING SLOWLY SOUTHWESTWARD ALONG THE NORTHERN PERIPHERY
OF A BUILDING SUBTROPICAL RIDGE (STR) CENTERED NORTHEAST OF SYDNEY.
THE SHEAR HAS DROPPED A NOTCH FROM THE PEAK SEEN YESTERDAY, BUT
STILL REMAINS AT MODERATE LEVELS AND CONTINUES TO BE A SIGNIFICANT
FACTOR IN THE SYSTEMS EROSION, THOUGH THE PACE OF THE WEAKENING HAS
EASED SLIGHTLY. SIGNIFICANT AMOUNTS OF MID-LEVEL DRY AIR ARE BEING
ADVECTED INTO THE SYSTEM, PARTICULARLY ACROSS THE NORTHERN HALF OF
THE CIRCULATION. COMBINED, THE SHEAR AND DRY AIR ARE CONTRIBUTING
TO THE STEADY WEAKENING BEING OBSERVED.

INITIAL WIND RADII BASIS: PERSISTENCE 

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   ABRF: T4.5 - 77 KTS
   CIMSS SATCON: 60 KTS AT 091509Z
   CIMSS ADT: 59 KTS AT 091730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY
UNFAVORABLE
   VWS: 20-25 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY MID-LEVEL AIRMASS

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TC 03P (JASPER) IS FORECAST TO CONTINUE
TRACKING TOWARDS THE WEST-SOUTHWEST ALONG THE NORTHERN SIDE OF THE
STEERING RIDGE OVER THE NEXT 24 HOURS. AFTER TAU 24, THE RIDGE TO
THE SOUTH WILL PUSH NORTHWARD AND REPOSITION TO A POINT TO THE
NORTHWEST OF BRISBANE, PUSHING TC 03P ONTO A MORE NORTHWESTWARD
TRACK UNTIL ABOUT TAU 72. BY TAU 72, THE STR TO THE SOUTH BECOMES
MORE ENTRENCHED OVER EASTERN AUSTRALIA AND THE TRACK OF TC 03P WILL
FLATTEN OUT ON A GENERALLY WESTWARD TRACK THROUGH THE REMAINDER OF
THE FORECAST PERIOD. LANDFALL IS EXPECTED AROUND TAU 84 ALONG THE
EASTERN COAST OF AUSTRALIA, NORTH OF CAIRNS, AFTER WHICH THE SYSTEM
WILL CONTINUE MOVING WEST TOWARDS THE GULF OF CARPENTARIA. IN TERMS
OF INTENSITY, WIND SHEAR IS FORECAST BY THE GLOBAL MODELS TO REMAIN
AT MODERATE LEVELS OVER THE NEXT 24 HOURS, BEFORE DECREASING
SHARPLY AFTER TAU 36. WHILE THIS WOULD ARGUE IN FAVOR OF
REINTENSIFICATION, THE UPPER-LEVEL FLOW PATTERN IS EXPECTED TO BE
SOMEWHAT CONVERGENT, WHICH COMBINED WITH THE PERSISTENT MID-LEVEL
DRY AIR, WILL OFFSET THE DECREASED SHEAR AND LEAD TO A CONTINUED
WEAKENING TREND THROUGH THE NEXT 36 HOURS. THE UPPER-LEVEL FLOW
PATTERN SHIFTS AGAIN AFTER TAU 48 AND BECOMES MORE DIVERGENT, WITH
THE GFS INDICATING DEVELOPMENT OF AN UPPER-LEVEL POINT SOURCE OVER
TOP OF THE SYSTEM BY TAU 72, PROVIDING THE IMPETUS FOR A
REINTENSIFICATION PHASE AFTER TAU 48, CONTINUING THROUGH LANDFALL.
THE RELATIVELY SHORT DURATION OF THE FAVORABLE CONDITIONS PRIOR TO
LANDFALL WILL SERVE TO CAP THE PEAK INTENSITY SOMEWHAT, BUT A PEAK
BETWEEN 60-65 KNOTS IS POSSIBLE JUST PRIOR TO LANDFALL, OCCURRING
BETWEEN THE FORECAST POINTS. RAPID WEAKENING IS ANTICIPATED AFTER
THE SYSTEM MOVES INLAND, WITH DISSIPATION BELOW WARNING CRITERIA
ANTICIPATED BY TAU 120 AS IT REACHES THE EASTERN EDGE OF THE GULF
OF CARPENTARIA.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT
THROUGH THE ENTIRE FORECAST PERIOD, WITH ONLY MODERATE SPREAD
BECOMING EVIDENT AFTER LANDFALL AS THE SYSTEM WEAKENS. CROSS-TRACK
SPREAD INCREASES TO 110NM AT TAU 72, BETWEEN GFS ON THE NORTHERN
EDGE AND ECMWF ON THE SOUTHERN EDGE OF THE GUIDANCE ENVELOPE.
CROSS-TRACK SPREAD REMAINS STEADY THROUGH TAU 120 BUT ALONG-TRACK
SPREAD INCREASES SHARPLY TO 310NM AS THE ECMWF AND GALWEM MODELS
RACE THE SYSTEM ACROSS THE CAPE YORK PENINSULA, WHILE THE GFS HOLDS
THE SYSTEM BACK, KEEPING IT EAST OF THE GREAT DIVIDING RANGE. THE
JTWC FORECAST LIES JUST NORTH OF THE CONSENSUS MEAN WITH MEDIUM
CONFIDENCE TO TAU 72, DECREASING TO LOW CONFIDENCE IN THE EXTENDED
RANGE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT IN BOTH THE OVERALL
SHAPE OF THE TREND LINE AND THE INTENSITY VALUES. THE JTWC FORECAST
LIES CLOSE TO THE CONSENSUS MEAN THROUGHOUT THE FORECAST PERIOD,
WITH MEDIUM CONFIDENCE. 

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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