TC 12P//Remnants of TC 11P(OSAI)// 10P(NAT) Subtropical// INVEST 90S// 10 DAY ECMWF Storm Tracks//0909utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 12P. 3HOURLY SATELLITE BULLETINS ARE ISSUED ON THE REMNANTS OF TC 11P(OSAI) AND ON SUBTROPICAL STORM 10P(NAT).

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TROPICAL CYCLONE (TC) 12P (TWELVE) CONTINUES TO STRUGGLE AGAINST PERSISTENT NORTHWESTERLY SHEAR BUT MAINTAINS MINIMAL TC STRENGTH. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THAT THE LOW LEVEL CIRCULATION CENTER (LLCC) REMAINS HIGHLY ELONGATED, STRETCHED OUT ALONG A NORTHWEST-SOUTHEAST AXIS. THIS CONFIGURATION OF THE LLCC WAS CONFIRMED BY EARLIER ASCAT-B AND -C PASSES FROM 082151Z AND 082243Z RESPECTIVELY. BOTH SCATTEROMETER PASSES SHOWED A HIGHLY ASYMMETRIC LLCC WITH WINDS BARELY EXCEEDING 30 KNOTS. LATER SCATTEROMETER DATA FROM 090443Z SHOWS A SIMILAR WIND FIELD SETUP, BUT SHOWS A MORE DEFINED AND CONSOLIDATED CIRCULATION CENTER. THE LATEST ANIMATED MSI SHOWED HINTS OF THE LLCC STARTING TO CONSOLIDATE JUST EAST OF AN AREA OF EXPLOSIVE CONVECTIVE DEVELOPMENT, WHICH KICKED OFF AROUND 0500Z. IF THE LLCC CAN SUCCESSFULLY MOVE UNDER THIS CONVECTION, THEN THINGS WILL GET INTERESTING. IN THE MEANTIME, ENVIRONMENTAL CONDITIONS REMAIN MARGINALLY FAVORABLE, WITH PERSISTENT, BUT WEAKENING NORTHWESTERLY SHEAR AND DRY MID-LEVEL AIR TO THE WEST OFFSETTING WARM SSTS AND STRONG POLEWARD OUTFLOW. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON TRACKING OF THE LLCC IN HIGH-RESOLUTION VISIBLE IMAGERY AND EXTRAPOLATION OF A LOW EMISSIVITY REGION IN A 090443Z SSMIS 37GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS SET WITH MEDIUM CONFIDENCE BASED ON THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES OUTLINED BELOW.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 12P IS FORECAST TO CONTINUE TRACKING EAST-SOUTHEASTWARD THROUGH THE FIRST 48-60 HOURS OF THE FORECAST, ALONG THE SOUTHERN SIDE OF A STRONG NER TO THE NORTHEAST. AROUND TAU 48, THE RIDGE BEGINS TO BUILD SOUTHWARD AND EVENTUALLY PINCHES OFF INTO A SEPARATE SUBTROPICAL RIDGE (STR) CENTERED NEAR 20S 170W. THIS PROCESS OF STR DEVELOPMENT WILL EFFECTIVELY BLOCK TC 12P FROM TRAVELING FURTHER EAST AFTER TAU 72. THE FORECAST THUS CALLS FOR THE SYSTEM TO SLOW DOWN AFTER TAU 48 AND BECOME QUASI-STATIONARY AFTER TAU 72. IN TERMS OF INTENSITY, CURRENTLY THE SYSTEM CAN BARELY BE CATEGORIZED AS A MINIMAL TROPICAL CYCLONE. THE OVERALL ENVIRONMENT LOOKS SET TO IMPROVE SLIGHTLY OVER THE NEXT 12 HOURS, WITH A REDUCTION IN DEEP-LAYER SHEAR AND A SLIGHT MID-LEVEL MOISTENING ANTICIPATED. THIS SHOULD ALLOW THE SYSTEM TO CONSOLIDATE THE VORTEX A BIT AND THE FIRST HINTS OF THIS MAY BE BEING SEEN NOW. IF THIS PROCESS DOES IN FACT OCCUR AS EXPECTED, THEN A SLIGHT INTENSIFICATION UP TO 40 KNOTS IS FORECAST, WITH THIS INTENSITY PERSISTING THROUGH TAU 36 AS THE SYSTEM PASSES SOUTH OF PORT VILA, VANUATU. INCREASING SHEAR AND ESPECIALLY A SIGNIFICANT INFLUX OF DRY MID-LEVEL AIR EXPECTED AFTER TAU 48, WILL RAPIDLY SMOTHER WHAT REMAINS OF THE SYSTEM AND MARK THE ONSET OF RAPID WEAKENING AND DISSIPATION. DISSIPATION BELOW WARNING THRESHOLD IS FORECAST NO LATER THAN TAU 96 AND COULD PLAUSIBLY OCCUR AS EARLY AS TAU 72.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN MODEST AGREEMENT THROUGH TAU 48, WITH ALL OF THE CONSENSUS MEMBERS CONCURRING THAT THE SYSTEM WILL TRACK STEADILY EAST-SOUTHEASTWARD THROUGH THIS TIME PERIOD. CROSS-TRACK SPREAD IS MINIMAL THROUGH TAU 48, THOUGH ALONG-TRACK SPREAD BEGINS TO REAR ITS UGLY HEAD EVEN AT THIS EARLY POINT IN THE FORECAST, WITH THE NAVGEM PULLING AWAY AHEAD OF THE PACK WHILE THE GFS LAGS BEHIND. BY TAU 72, THE WHEELS FALL OFF THIS WAGON AND THE MODELS START TO WIDELY DIVERGE IN THEIR TRACK SOLUTIONS, WITH A TRIPLE OPTION SETTING UP. THE NAVGEM AND GALWEM PUSH THE SYSTEM STRAIGHT AHEAD TO A POSITION SOUTH OF FIJI, THE US MODELS TURN THE SYSTEM NORTH THEN NORTHWEST AND THE EUROPEAN MODELS TURN SOUTH THEN SOUTHWEST. THE RESULTING MODEL CONFIGURATION CAN BEST BE DESCRIBED AS A DRAWN BOW WITH THE ARROW POINTING STRAIGHT AHEAD, INTRODUCING SIGNIFICANT UNCERTAINTY AND LENDING LOW CONFIDENCE IN THE TRACK, ESPECIALLY AFTER TAU 48. INTENSITY GUIDANCE ALSO SHOWS A WIDE DISPARITY, WITH THE SHIPS GUIDANCE SHOWING STEADY INTENSIFICATION TO GREATER THAN 80 KNOTS WHILE THE HAFS-A SHOWS THE SYSTEM DISSIPATING IN THE NEXT 12 HOURS. THE COAMPS-TC (BOTH NAVGEM AND GFS) SEEM THE MOST REALISTIC, IN SHOWING A MARGINAL INTENSIFICATION IN THE FIRST 24 HOURS FOLLOWED BY A DISSIPATION BY THE END OF THE FORECAST. BUT WITH SUCH A LARGE SPREAD IN THE GUIDANCE, THE JTWC FORECAST IS SET WITH LOW CONFIDENCE.

THE AREA OF CONVECTION (REMNANTS 10P) PREVIOUSLY LOCATED NEAR 19.4S 147.5W IS NOW LOCATED NEAR 19.5S 145.2W, APPROXIMATELY 287 NM EAST-SOUTHEAST OF PAPEETE, TAHITI. THE SYSTEM IS CURRENTLY CLASSIFIED AS A SUBTROPICAL CYCLONE, GENERALLY CHARACTERIZED AS HAVING BOTH TROPICAL AND MIDLATITUDE CYCLONE FEATURES. ANIMATED VISIBLE SATELLITE IMAGERY DEPICTS A WARM CORE ASYMMETRIC SYSTEM WITH CONVECTION THAT HAS BEEN SHEARED TO THE SOUTHEAST OF A PARTIALLY EXPOSED LOW LEVEL CIRCULATION (LLC), TYPICAL OF A SUBTROPICAL SYSTEM. A PREVIOUS AMSR2 89GHZ MICROWAVE PASS REVEALED AN ELONGATED LLC THAT IS STILL HOLDING ON TO ROBUST FLARING CONVECTION DESPITE THE HIGH LEVELS OF WIND SHEAR. ENVIRONMENTAL ANALYSIS REVEALS UNFAVORABLE CONDITIONS FOR TROPICAL TRANSITION DEFINED BY A DEEP LAYER OF DRY AIR BEING ADVECTED OVER THE CIRCULATION, STRONG WESTERLIES ALOFT, AND HIGH (GREATER THAN 40KTS) VERTICAL WIND SHEAR. GLOBAL MODELS ARE IN AGREEMENT THAT THE REMNANTS OF TC 10P WILL TRACK SOUTHEASTWARD WITH A BROAD AND ASYMMETRIC WIND FIELD. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 38 TO 43 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 998 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS LOW.