92S now TC 14S(VERNON): forecast to merge with Invest 93S//Invest 99S: High, Invest 98P: Low//13S(EMNATI):subtropical,25/09utc

JTWC IS ISSUING 12HOURLY WARNINGS ON TC 14S(VERNON). 3HOURLY SATELLITE BULLETINS ARE ISSUED ON 14S, 99S AND 98P. THEY WERE DISCONTINUED ON 13S(EMNATI) AT 25/0530UTC.

25/0930UTC.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: THROUGH THE FIRST 24 HOURS OF THE FORECAST, THERE IS GOOD CERTAINTY, AS THE PRIMARY DRIVER OF THE TRACK WILL BE THE SUBTROPICAL RIDGE (STR) CENTERED TO THE SOUTH. HOWEVER, THE PRESENCE OF INVEST 93S, CURRENTLY APPROXIMATELY 550KM TO THE NORTHWEST, WILL HAVE A SIGNIFICANT AND HIGHLY UNCERTAIN IMPACT ON THE FORECAST AFTER 24H. CURRENT DETERMINISTIC AND ENSEMBLE GLOBAL MODELS SUGGEST THAT INVEST 93S WILL TRACK TO THE NORTH SIDE OF TC 14S, AND BEGIN BINARY INTERACTION IN THE NEXT 12 HOURS, SLOWLY STARTING TO WRAP IN CLOSER AND CLOSER TO TC 14S. ONCE 93S PASSES TO THE EAST OF DUE NORTH AROUND 36H, TC 14S IS EXPECTED TO TURN EQUATORWARD AS THE TWO SYSTEMS APPROACH CPA AND BEGIN TO FUJIWARA AROUND ONE ANOTHER. TC 14S WILL LIKELY PERFORM A CLOCKWISE LOOP THROUGH 48H, AND AGAIN TURN POLEWARD AFTER THIS POINT AS IT STARTS TO MERGE WITH INVEST 93S. MERGER IS EXPECTED TO BE COMPLETE BY AROUND 60H, AND TC 14S WILL VASTLY INCREASE IN SIZE. A PASSING MID-LATITUDE TROUGH WILL BREAK THE STEERING RIDGE AROUND THE SAME TIME, AND BY 72H, TC 14S WILL START MOVING POLEWARD ALONG THE WESTERN SIDE OF THE STR NOW CENTERED TO THE EAST. DUE THE VERY SMALL NATURE OF THE SYSTEM, SMALL-SCALE CHANGES IN THE ENVIRONMENT WILL HAVE OUTSIZED EFFECTS AND THUS THE INTENSITY FORECAST IS VERY UNCERTAIN. THE OVERALL ENVIRONMENT IS FAVORABLE INTENSIFICATION AND THE RECENT EVOLUTION OF THE SYSTEM SUGGESTS THAT WITHOUT SIGNIFICANT ENVIRONMENTAL CHANGES EXPECTED, IT SHOULD CONTINUE TO STEADILY INTENSIFY. ALL RAPID INTENSIFICATION AIDS WERE TRIGGERED WITH THIS CYCLE, AND THE FORECAST CALLS FOR A RAPID INTENSIFICATION TO 80 KNOTS/CAT 1 US WITHIN THE NEXT 36 HOURS. EVEN THOUGH THE ENVIRONMENT REMAINS FAVORABLE, THE DISRUPTION CAUSED BY THE BINARY INTERACTION WITH INVEST 93S WILL PUT THE BRAKES ON THE INTENSIFICATION TREND FROM 36H TO 48H AS THE SYSTEMS MERGE. ONCE MERGED INTO ONE LARGER SYSTEM, TC 14S WILL RESUME INTENSIFYING AS IT MOVES POLEWARD AND TAPS INTO ROBUST POLEWARD OUTFLOW INTO THE BASE OF A PASSING MID-LATITUDE TROUGH, REACHING A SECOND PEAK OF 95 KNOTS/CAT 2 US BY 96H, BEFORE WEAKENING SLIGHTLY AT THE END OF THE FORECAST PERIOD DUE TO STEADILY INCREASING SHEAR.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A VERY COMPACT SYSTEM, WHICH OVER THE PREVIOUS FEW HOURS HAS RAPIDLY CONSOLIDATED AND INTENSIFIED INTO A TROPICAL CYCLONE. THE PREVIOUS SIX-HOUR INTENSITY FROM 250000Z HAS BEEN REANALYZED AND IS NOW ASSESSED TO HAVE BEEN 35 KNOTS, INDICATING A 10 KNOT INTENSIFICATION IN THE LAST SIX HOURS. IN THE PAST COUPLE OF HOURS, ANIMATED MSI AND EIR SUGGEST THE DEVELOPMENT OF A DIMPLE AND WARM SPOT, SUGGESTIVE OF THE POSSIBILITY OF A NASCENT EYE FEATURE. HOWEVER, THE LACK OF ANY RECENT MICROWAVE IMAGERY PRECLUDES AND FULL UNDERSTANDING OF THE STORM STRUCTURE. THE INITIAL POSITION IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON AN EXTRAPOLATION OF THE WELL DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) IN A 250320Z ASCAT-C BULLSEYE PASS. THE INITIAL INTENSITY IS ASSESSED AT 45 KNOTS WITH MEDIUM CONFIDENCE, WELL ABOVE THE PGTW T2.5 ESTIMATE, BUT WELL BELOW THE T4.0 FROM APRF. CONSIDERABLE WEIGHT WAS GIVEN TO THE PREVIOUSLY MENTIONED ASCAT-C DATA WHICH INDICATED A FEW 45 KNOT WIND BARBS VERY NEAR THE CORE, THOUGH WITH SUCH A COMPACT CORE, ITS POSSIBLE THERE ARE HIGHER WINDS PRESENT THAT THE SCATTEROMETER RESOLUTION CAN'T PICK UP. ANALYSIS REVEALS A FAVORABLE ENVIRONMENT OF LOW VERTICAL WIND SHEAR, WARM SSTS, AND GOOD EQUATORWARD OUTFLOW ALOFT.

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE DEPICTS A LARGE AMOUNT OF UNCERTAINTY, PARTICULARLY AFTER 36H WHEN THE BINARY INTERACTION BEGINS. MOST OF THE GUIDANCE SUPPORTS THE QUASI-STATIONARY OR LOOPING MOTION BETWEEN ROUGHLY 36H TO 48H, BUT DIFFER ON HOW THE SYSTEM EMERGES OUT OF THE MERGER, RESULTING IN A VERY LARGE SPREAD IN THE GUIDANCE ENVELOPE AFTER 72H. THE UKMET MARKS THE EASTERN EDGE OF THE ENVELOPE, WHILE GFS MARKS THE WESTERN. THE JTWC FORECAST TRACKS THE GFS SOLUTION THROUGH 36H, HEN CLOSER TO THE HWRF THEREAFTER THOUGH HEDGES TOWARDS THE WESTERN SIDE OF THE ENVELOPE AFTER 48H. CONFIDENCE IS HIGH IN THE FIRST 24 HOURS, THEN LOW THEREAFTER DUE TO THE UNCERTAINTY SURROUNDING THE BINARY INTERACTION. THE INTENSITY GUIDANCE IS SIMILARLY UNCERTAIN, WITH A WIDE RANGE IN PEAK INTENSITIES BETWEEN 50 KNOTS AND 115 KNOTS. THE JTWC FORECAST TRACKS THE RI35 LINE THROUGH 36 HOURS, THEN FLATTENS OUT CLOSER TO THE DECAY SHIPS THROUGH 48H, BUT THEN ABOVE ALL THE GUIDANCE THROUGH THE REMAINDER OF THE FORECAST PERIOD. CONFIDENCE IS LOW THROUGH THE FORECAST AGAIN DUE TO UNCERTAINTY ASSOCIATED WITH THE SMALL SIZE OF THE SYSTEM AND THE IMPACTS OF THE BINARY INTERACTION.

THE AREA OF CONVECTION (INVEST 99S) PREVIOUSLY LOCATED NEAR 12.9S 128.6E IS NOW LOCATED NEAR 12.4S 128.4E, APPROXIMATELY 740KM WEST OF DARWIN, AUSTRALIA. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY AND A 241938Z SSMIS 91GHZ IMAGE REVEALS ELONGATED, DEEP CONVECTION FLARING OVER A WELL DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). A 241339 ASCAT-B PARTIAL IMAGE SHOWS 25-30 KT WINDS IN THE SOUTHWESTERN QUADRANT OF THE AREA. ENVIRONMENTAL ANALYSIS REVEALS THAT THE INVEST IS IN A FAVORABLE ENVIRONMENT FOR DEVELOPMENT DEFINED BY PRONOUNCED EQUATORWARD OUTFLOW AND WARM (30- 31C) SEA SURFACE TEMPERATURES. THESE ARE OFFSET BY UNFAVORABLE (25- 30KTS) VERTICAL WIND SHEAR AS DEPICTED ON THE 1800Z CIMSS DEEP LAYER WIND SHEAR ANALYSIS. OBSERVATIONS FROM PT. FAWCETT REPORT 15KT NORTHWESTERLY WINDS. GLOBAL MODELS ARE IN AGREEMENT REGARDING THE INTENSIFICATION AS THE SYSTEM MEANDERS IN THE GULF OF BONAPARTE OVER THE NEXT 24-48 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 25 TO 30 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO HIGH.

GLOBAL MODELS ARE IN AGREEMENT REGARDING THE INTENSIFICATION AS THE SYSTEM MEANDERS IN THE GULF OF BONAPARTE OVER THE NEXT 24-48 HOURS.

THE AREA OF CONVECTION (INVEST 93S) PREVIOUSLY LOCATED NEAR 12.2S 88.8E IS NOW LOCATED NEAR 12.2S 89.2E, APPROXIMATELY 830KM SOUTHWEST OF COCOS ISLANDS. ANIMATED MULITSPECTRAL IMAGERY DEPICTS DEEP CONVECTION CONSOLIDATING OVER AN OBSCURED LOW LEVEL CIRCULATION WHILE RECENT SCATTEROMETER DATA REVEALED 25-30KTS WINDS WRAPPING INTO THE AFORMENTIONED LOW LEVEL VORTEX. THE ENVIRONMENT IS CONDUCIVE FOR TROPCIAL CYCLONE DEVELOPMENT WITH LOW (10-15KTS) VERTICAL WIND SHEAR, WARM (29-30C)SEA SURFACE TEMPERATURES AND MODERATE POLEWARD OUFLOW. MODELS AGREE THAT THE SYSTEM WILL TRACK EAST, BUT FURTHER DEVELOPMENT IS COMPLICATED AS 93S WILL HAVE TO COMPETE WITH ITS TWIN SYSTEM, 92S. THERE IS A BRIEF WINDOW FOR 93S TO INTENSIFY AND REACH 35KTS AS THE TWO STORMS BEGIN BINARY INTERACTION AND DANCE. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1004 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO LOW

AN AREA OF CONVECTION (INVEST 98P) PREVIOUSLY LOCATED NEAR 11.0S 144.3E IS NOW LOCATED NEAR 11.3S 144.9E, APPROXIMATELY 315KM SOUTHWEST OF PORT MORESBY, PAPA NEW GUINEA. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A LOW LEVEL CIRCULATION (LLC) WITH FLARING CONVECTION. ENVIRONMENTAL ANALYSIS INDICATES OVERALL FAVORABLE DEVELOPMENT FOR TROPICAL CYCLONE FORMATION WITH LOW TO MODERATE (15-20KT) VERTICAL WIND SHEAR, GOOD RADIAL OUTFLOW, AND VERY WARM (30-31C) SEA SURFACE TEMPERATURES. GLOBAL MODELS ARE IN AGREEMENT THAT THE SYSTEM WILL CONTINUE TO TRACK EASTWARD AND DEVELOP WITHIN THE NEXT 48-72HRS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 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 LOW.

GLOBAL MODELS ARE IN AGREEMENT THAT THE SYSTEM WILL CONTINUE TO TRACK EASTWARD AND DEVELOP WITHIN THE NEXT 48-72HRS.

SUBTROPICAL SYSTEM SUMMARY: THE AREA OF CONVECTION (REMNANTS OF TC 13S) PREVIOUSLY LOCATED NEAR 28.7S 41.8E IS NOW LOCATED NEAR 29.7S 41.7E, APPROXIMATELY 710KM SOUTH OF TOLIARA, MADAGASCAR. THE SYSTEM IS CURRENTLY CLASSIFIED AS A SUBTROPICAL STORM, GENERALLY CHARACTERIZED AS HAVING BOTH TROPICAL AND MID- LATITUDE CYCLONE FEATURES. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A FULLY EXPOSED, ELONGATED AND DISORGANIZED LOW LEVEL CIRCULATION CENTER (LLCC) WITH A BROAD DEFORMATION ZONE DISPLACED TO THE SOUTH. ENVIRONMENTAL ANALYSIS INDICATES A POOR ENVIRONMENT FOR TROPICAL CYCLONE DEVELOPMENT WITH A STRONG GRADIENT OF VERTICAL WIND SHEAR (20-50KTS) DECAPITATING THE UPPER AND LOWER LEVEL FEATURES AND COOLER SEA SURFACE TEMPERATURES (18-20C). GLOBAL MODELS AGREE THAT THE REMNANTS OF 13S WILL TRACK SOUTHEASTWARD, STRETCH, BECOME ASYMETRICAL, AND FULLY EMBEDDED IN THE BAROCLINIC ZONE INDICATING TROPICAL TRANSITION WILL BE UNLIKELY. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 38-43 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 989MB. FOR HAZARDS AND WARNINGS, REFERENCE THE FLEET WEATHER CENTER SAN DIEGO HIGH WINDS AND SEAS PRODUCT OR REFER TO LOCAL WMO DESIGNATED FORECAST AUTHORITY. THE POTENTIAL FOR THE SYSTEM TO TRANSITION INTO A SIGNIFICANT TROPCIAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS LOW.

GLOBAL MODELS AGREE THAT THE REMNANTS OF 13S WILL TRACK SOUTHEASTWARD, STRETCH, BECOME ASYMETRICAL, AND FULLY EMBEDDED IN THE BAROCLINIC ZONE INDICATING TROPICAL TRANSITION WILL BE UNLIKELY.