Tropical Cyclone 03P(JASPER) peaked at US CAT 4, now weakening under strong shear//0906utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 03P(JASPER).

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.

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.