TS 09W(MEARI) slowly intensifying north of 30°N//Arabian Sea:TC 03A rapidly emerging//Invest 90E: TCFA// Invest 90C, 12/09utc

JTWC IS ISSUING 6HOURLY WARNINGS ON TS 09W AND TC 03A. 3HOURLY SATELLITE BULLETINS ARE ISSUED ON BOTH SYSTEMS AND ON INVEST 90C.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT THE EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) THAT HAS BEEN TRACKED OVER THE PAST DAY, HAS STOPPED MOVING NORTHWARD AND HAS INSTEAD TAKEN A HARD TURN TO THE EAST OVER THE PAST FOUR HOURS OR SO. NET TRACK MOTION SINCE THE PREVIOUS BEST TRACK HAS THUS SLOWED TO ROUGHLY FIVE KNOTS. TS 09W CONTINUES TO STRUGGLE TO CONSOLIDATE AN ORGANIZED CONVECTIVE CORE ABOUT THE LLCC IN THE FACE OF PERSISTENT NORTH-NORTHWESTERLY SHEAR. HOWEVER, THE BULK SHEAR, WHILE STILL MODERATE, HAS SLACKED OFF QUITE A BIT SINCE THE PREVIOUS ANALYSIS, NOW ESTIMATED AT 15-20 KNOTS. ATMOSPHERIC MOTION VECTORS (AMVS) REVEAL AN UPPER-LEVEL COL REGION JUST NORTH OF TD 09W AND AS THE SYSTEM MOVES INTO THIS REGION, SHEAR IS EXPECTED TO SLACKEN EVEN MORE. JTWC HAND ANALYSIS INDICATES A MINISCULE POINT SOURCE LOCATED ABOVE TS 09W, PROVIDING MODERATE TO STRONG EQUATORWARD OUTFLOW AND SUPPORTING THE FLARING CONVECTION IN THE SOUTHERN HEMISPHERE OF THE SYSTEM. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC. THE INITIAL INTENSITY REMAINS ASSESSED AT 35 KNOTS WITH HIGH CONFIDENCE BASED ON AN OVERALL AVERAGE OF AGENCY SUBJECTIVE AND OBJECTIVE DVORAK FIX INTENSITIES. REGARDLESS OF THE RECENT RIGHTWARD JOG OF THE LLCC, THE OVERALL MOTION CONTINUES NORTHWARD ALONG THE WESTERN PERIPHERY OF A DEEP SUBTROPICAL RIDGE (STR) ENTRENCHED TO THE EAST.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 09W IS FORECAST TO CONTINUE TO TRACK NORTH-NORTHEASTWARD ALONG THE WESTERN PERIPHERY OF THE STEERING RIDGE THROUGH THE NEXT 12 HOURS. THEN AS THE RIDGE RAPIDLY SLIDES SOUTHWESTWARD AFTER TAU 24, TS 09W WILL TURN ONTO A NORTHEASTWARD TRACK THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE SYSTEM IS FORECAST TO MAKE LANDFALL ALONG THE SOUTHERN TIP OF THE IZU PENINSULA AROUND TAU 24, THEN MOVE THROUGH THE SOUTHERN PORTION OF THE TOKYO WAN, THEN BACK OUT TO SEA EAST OF NARITA BY AROUND TAU 30, THEN CONTINUE TO ACCELERATE NORTHEAST TO NEAR THE CENTRAL KURIL ISLANDS BY THE END OF THE FORECAST PERIOD. AS DISCUSSED ABOVE, TS 09W CONTINUES TO STRUGGLE TO CONSOLIDATE A VERTICALLY STACKED CONVECTIVE CORE IN THE FACE OF PERSISTENT NORTHERLY FLOW. AS THE SYSTEM CONTINUES TRACKING NORTHWARD AND ENTERS A COL REGION OF RELATIVELY LIGHT WINDS, SHEAR IS FORECAST TO BACK OFF TO LOW LEVELS. AT THE SAME TIME THE SYSTEM WILL MOVE INTO AN AREA OF STRONGLY DIFFLUENT WESTERLY FLOW ALOFT, ENHANCING THE POLEWARD AND EASTWARD OUTFLOW. THE COMBINATION OF THESE TWO FACTORS SHOULD BE ENOUGH TO ALLOW THE CONVECTIVE CORE TO CONSOLIDATE AND INITIATE A SHORT BURST OF INTENSIFICATION. DUE TO THE LIMITED TIME REMAINING OVER OPEN WATERS AND THE VERY SHORT WINDOW DURING WHICH THE ABOVE FACTORS MUST CONGEAL, THE FORECAST PEAK IS ONLY 50 KNOTS BY TAU 24 AS THE SYSTEM APPROACHES LANDFALL. AFTER RETURNING TO OPEN WATERS EAST OF HONSHU, THE SYSTEM WILL BEGIN EXTRATROPICAL TRANSITION (ETT) AS IT MOVES AHEAD OF A NEGATIVELY TILTED 200MB TROUGH, AND CROSSES INTO MUCH COOLER WATERS (LESS THAN 24C). THE SYSTEM WILL ALSO BE RAPIDLY WEAKENING AS IT UNDERGOES ETT AND IT WILL BE A RACE TO SEE WHICH OCCURS FIRST, DISSIPATION OR ETT. AT THIS POINT, THE FORECAST FAVORS TRANSITION TO A COLD CORE BAROTROPIC EXTRATROPICAL SYSTEM PRIOR TO DISSIPATION BELOW WARNING CRITERIA, WITH TRANSITION OCCURRING NO LATER THAN TAU 72, AND LIKELY BY TAU 60.

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN EXTREMELY GOOD AGREEMENT THROUGH THE BULK OF THE FORECAST, WITH A MINIMAL 40NM SPREAD AT TAU 24, INCREASING TO ABOUT 200NM AT THE END OF THE FORECAST PERIOD. THE JGSM MODEL IS THE SOLE BLACK SHEEP OF THE FAMILY, HANGING OUT ABOUT 50NM WEST OF THE REMAINDER OF THE GUIDANCE PACKAGE THROUGH THE DURATION OF THE FORECAST. THE JTWC TRACK FORECAST LIES ON THE LEFT SIDE OF THE GUIDANCE ENVELOPE THROUGH TAU 24, THEN CLOSELY FOLLOWS THE CONSENSUS MEAN THEREAFTER WITH HIGH CONFIDENCE. INTENSITY GUIDANCE SHOWS MORE VARIABILITY WITH THIS RUN, WITH THE CTCX AND CTR1 BACK TO THEIR OLD TRICKS, INDICATING A PEAK NEAR 70 KNOTS, SIGNIFICANTLY ABOVE THE REMAINDER OF THE GUIDANCE WHICH LIES IN A TIGHT 10 KNOT ENVELOPE BETWEEN 40-50 KNOTS. THE DECAY-SHIPS IS ALSO A SIGNIFICANT OUTLIER ON THE LOW SIDE, WITH BOTH THE GFS AND NAVGEM VERSION INDICATING WEAKENING FROM THE START. THE JTWC FORECAST REMAINS CONSISTENT WITH THE PREVIOUS FORECAST AND PEAKS AT 50 KNOTS, ON THE HIGH END OF THE TIGHTEST MODEL PACKING. CONFIDENCE IN THE FORECAST IS MEDIUM HOWEVER, DUE TO THE UNCERTAINTIES BROUGHT ON BY THE VERY TIGHT WINDOW OF OPPORTUNITY FOR ALL THE POSITIVE ENVIRONMENTAL FACTORS TO ALIGN AND TS 09W TO INTENSIFY.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A SHEARED SYSTEM, WITH DEEP FLARING CONVECTION DISPLACED TO THE WEST OF A PARTIALLY OBSCURED LOW LEVEL CIRCULATION CENTER (LLCC). TC 03A HAS EMERGED OFF THE GUJARAT PENINSULA AND MOVED WESTWARD UNDER A MARGINALLY FAVORABLE UPPER-LEVEL FLOW PATTERN, WHICH ALLOWED FOR A BRIEF BURST OF CONVECTIVE DEVELOPMENT AND ORGANIZATION. JTWC HAND ANALYSIS OF 120000Z UPPER-LEVEL ATMOSPHERIC MOTION VECTORS (AMVS) REVEALED A POINT SOURCE OVER TOP OF THE LLCC, WHICH HAS INDUCED RELATIVELY LOW SHEAR, IN THE 10-15 KNOT RANGE. SUBSEQUENT AMVS REVEAL THIS POINT SOURCE IS MOVING OFF TO THE WEST OF THE LLCC, LEAVING IT VULNERABLE TO INCREASING EASTERLY PRESSURE AND SHEAR, ALREADY STARTING TO INCREASE. A 120044Z SSMIS 91GHZ MICROWAVE IMAGE REVEALS DISORGANIZED DEEP CONVECTION CURVED CYCLONICALLY IN TOWARDS THE CENTER, THROUGHOUT THE WESTERN HEMISPHERE OF THE SYSTEM. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EXTRAPOLATION OF THE MICROWAVE IMAGERY AND THE PGTW FIX POSITION. A 120620Z ASCAT-B PARTIAL PASS REVEALED 35-40 KNOT WINDS IN THE WESTERN HEMISPHERE OF THE CIRCULATION, LENDING INCREASED CONFIDENCE TO THE INITIAL INTENSITY, WHICH IS NUDGED HIGHER THAN THE AGENCY DVORAK FIXES. THE SYSTEM LIES IN A MARGINAL ENVIRONMENT WITH WARM (28-29C) SSTS, MODERATE VWS (20-25 KTS) AND STRONG EQUATORWARD OUTFLOW. THE SYSTEM LIES IN A WEAK STEERING ENVIRONMENT, CAUGHT IN A COL REGION BETWEEN A RIDGE OVER THE SAUDI PENINSULA, A WESTWARD EXTENSION OF THE STR OVER FAR NORTHERN INDIA AND A NEAR EQUATORIAL RIDGE (NER) JUST SOUTHWEST OF SOUTHERN INDIA.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TC 03A RAPIDLY DEVELOPED AND INTENSIFIED TO A TROPICAL STORM STRENGTH AFTER EMERGING OVER WATER. NOW THAT ITS MOVED INTO THE NORTH-CENTRAL NORTH ARABIAN SEA, IT HAS MOVED INTO A WEAK STEERING PATTERN, TRAPPED BETWEEN COMPETING STEERING INFLUENCES OF A SERIES OF DEEP-LAYER RIDGES TO THE WEST, NORTH AND SOUTH. OVER THE NEXT 24 TO 36 HOURS, THE WESTERN EXTENSION OF RIDGE TO THE NORTH IS EXPECTED TO RECEDE AND WEAKEN, AND THE SOUTHERN RIDGE WILL BECOME THE DOMINANT STEERING MECHANISM, WITH THE RIDGE OF THE SAUDI PENINSULA ACTING AS A BLOCK TO MUCH FURTHER WESTWARD MOVEMENT. AS THE NER TO THE SOUTH MOVES DRIFTS NORTHWARD, IT WILL PUSH TC 03A NORTH AS WELL, WITH THE SYSTEM FORECAST TO SLOWLY MOVE NORTHWEST THEN NORTH THROUGH THE FORECAST PERIOD. THE BEST ENVIRONMENTAL CONDITIONS ARE OCCURRING NOW OR LIKELY ALREADY COME AND GONE, AND THUS THE SYSTEM IS LIKELY TO EXPERIENCE ONLY A VERY SHORT WINDOW OF OPPORTUNITY FOR FURTHER INTENSIFICATION, WITH A PEAK OF 40 KNOTS POSSIBLE BY TAU 12. THEREAFTER, AS THE UPPER-LEVEL POINT SOURCE DISSIPATES AND MOVES AWAY, THE GENERALLY STRONG EASTERLY FLOW ALOFT ASSOCIATED WITH THE TROPICAL EASTERLY JET (TEJ) WILL MOVE IN ONCE MORE, AND SHEAR THE SYSTEM APART. THIS WILL BE ACCOMPANIED BY AN INFLUX OF DRY AND DUSTY AIR FROM THE DESERTS OF AFGHANISTAN AND PAKISTAN, WHICH WILL SMOTHER ANY REMNANT CONVECTION, LEAVING AN EXPOSED AND STEADILY WEAKENING CIRCULATION WHICH IS EXPECTED TO DISSIPATE AS A TROPICAL CYCLONE NO LATER THAN TAU 36.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GENERAL AGREEMENT, AT LEAST THROUGH THE DURATION OF THE FORECAST, WITH ALL CONSENSUS MEMBERS AGREEING ON A SLOW WEST-NORTHWESTWARD TRACK THROUGH TAU 24, FOLLOWED BY A SHARP TURN TO THE NORTH-NORTHEAST BY TAU 36. SPREAD IS ROUGHLY 140NM BETWEEN THE BULK OF THE MODELS, WITH GFS ON THE FAR WEST AND ECMWF ON THE FAR EAST SIDE OF THE ENVELOPE. NAVGEM MEANWHILE IS DISCOUNTED AS IT TRACKS THE CIRCULATION BACK OVER LAND EAST OF KARACHI BY TAU 36, WHICH IS HIGHLY UNREALISTIC. THE JTWC FORECAST LIES CLOSE TO THE CONSENSUS MEAN WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS ALSO IN FAIRLY GOOD AGREEMENT, WITH HWRF, COAMPS-TC AND DECAY-SHIPS (GFS) INDICATING A PEAK OF 40 KNOTS AT TAU 12 FOLLOWED BY STEADY WEAKENING TO 30 KNOTS BY TAU 36. THE JTWC FORECAST LIES ON THE CONSENSUS MEAN THROUGH TAU 12 AND DISSIPATES THE SYSTEM AT 30 KNOTS BAY TAU 36, IN LINE WITH THE BULK OF THE GUIDANCE, WITH MEDIUM CONFIDENCE.

FORMATION OF A SIGNIFICANT TROPICAL CYCLONE IS POSSIBLE WITHIN 150 NM EITHER SIDE OF A LINE FROM 14.3N 106.8W TO 17.3N 112.4W WITHIN THE NEXT 12 TO 24 HOURS. AVAILABLE DATA DOES NOT JUSTIFY ISSUANCE OF NUMBERED TROPICAL CYCLONE WARNINGS AT THIS TIME. WINDS IN THE AREA ARE ESTIMATED TO BE 22 TO 27 KNOTS. METSAT IMAGERY AT 120600Z INDICATES THAT A CIRCULATION CENTER IS LOCATED NEAR 14.5N 107.2W. THE SYSTEM IS MOVING WEST-NORTHWESTWARD AT 09 KNOTS. 2. REMARKS: AN AREA OF CONVECTION (INVEST 90E) HAS PERSISTED NEAR 14.5N 107.2W, APPROXIMATELY 524 NM SOUTH-SOUTHEAST OF CABO SAN LUCAS, MEXICO. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AND A 120107Z SSMIS 91GHZ IMAGE DEPICT A MORE CONSOLIDATED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH CONVECTIVE BANDS ON THE NORTHERN AND SOUTHERN PERIPHERY WRAPPING INTO THE CENTER. ENVIRONMENTAL ANALYSIS INDICATES THE DISTURBANCE REMAINS UNDER AN AREA OF FAVORABLE (5-10 KNOTS) VERTICAL WIND SHEAR, WITH GOOD RADIAL OUTFLOW IN THE UPPER LEVELS, AND WARM (29-30C) SEA SURFACE TEMPERATURES. GLOBAL MODELS AGREE ON INVEST 90E TRACKING WEST-NORTHWEST AND DEVELOPING TO AT LEAST TROPICAL DEPRESSION STRENGTH BEFORE MOVING INTO AN AREA OF STRONG SHEAR BY TAU 72. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 22 TO 27 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1002 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS HIGH.