TC 14S(VERNON): rapid intensification: already a 70kts TC// Invest 99S now TC 15S//Invest 93S: Medium//13S(EMNATI) & Invest 98P, 25/15utc

JTWC IS ISSUING 12HOURLY WARNINGS ON TC 14S(VERNON) AND 6HOURLY WARNINGS ON TC 15S. 3HOURLY SATELLITE BULLETINS ARE ISSUED ON 14S,15S, INVEST 93S AND INVEST 98P.

25/1430UTC.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST PHILOSOPHY, HOWEVER DUE TO THE RECENT RAPID INTENSIFICATION, THIS FORECAST IS BEING ISSUED OFF-CYCLE TO CAPTURE INTENSIFICATION TREND AND ADJUST THE PEAK INTENSITY FORECAST. FORECAST DISCUSSION: TC 14S WILL CONTINUE TRACKING WEST-SOUTHWEST THROUGH 12H ALONG THE NORTHERN SIDE OF THE SUBTROPICAL RIDGE (STR). AFTER THIS POINT THE FORECAST GETS INTERESTING, AS TC 14S WILL BEGIN BINARY INTERACTION WITH INVEST 93S, CURRENTLY LOCATED APPROXIMATELY 550KM TO THE NORTHWEST. INVEST 93S IS TWO DEGREES EQUATORWARD OF TC 14S, AND THUS WILL MOVE TO A POSITION TO THE NORTH OF TC 14S AS IT TRACKS EASTWARD AND SLOWLY SPIRALS IN CLOSER TO TC 14S. AS 93S PASSES TO THE NORTH, TC 14S WILL BEGIN TO TRACK TOWARDS THE NORTHWEST AS THE TWO SYSTEMS BEGIN TO FUJIWARA ABOUT ONE ANOTHER. TC 14S WILL COMPLETE A CLOCKWISE LOOP AND THE TWO SYSTEMS ARE EXPECTED TO MERGE INTO ONE LARGER SYSTEM AROUND 48H. AS THIS IS OCCURRING, FAR TO THE SOUTH A MID-LATITUDE TROUGH WILL ERODE THE STEERING RIDGE FROM WEST TO EAST, ALLOWING FOR TC 14S TO TURN POLEWARD AFTER 48H, ACCELERATING SOUTH-SOUTHWEST THROUGH THE REMAINDER OF THE FORECAST. FROM AN INTENSIFICATION STANDPOINT, THE SYSTEM IS COCOONED WITHIN A VERY FAVORABLE ENVIRONMENT, BUT FOR ONLY ABOUT ANOTHER 24 HOURS, WHEN THE CORE WILL START TO BE DISRUPTED BY THE BINARY INTERACTION AND MERGER WITH 93S. THUS THE SYSTEM IS FORECAST TO INCREASE TO 100 KNOTS/CAT 3 US BY 24H, THEN LEVEL OFF AS IT MERGES WITH 93S, FOLLOWED BY A BRIEF SPURT OF REINTENSIFICATION TO A PEAK OF 105 KNOTS/CAT 3 US BY 48H. AFTER 72H THE SYSTEM WILL ENCOUNTER INCREASING VWS, WHICH WILL INITIATE A STEADY WEAKENING TREND THROUGH THE REMAINDER OF THE FORECAST PERIOD.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: TC 14S IS UNDERGOING A PERIOD OF VERY RAPID INTENSIFICATION, WITH THE INITIAL INTENSITY INCREASING FROM 45 KNOTS SIX HOURS AGO TO 70 KNOTS ON THIS WARNING. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A VERY COMPACT SYSTEM WITH A WELL DEFINED PINHOLE EYE HAVING RAPIDLY DEVELOPED SINCE THE 250900Z HOUR. AT 1200Z THE EYE MEASURED SLIGHTLY LESS THAN 19KM WIDE. EYE TEMPERATURES WERE STILL VERY COLD, BUT CLOUD TOP TEMPERATURES REACHED AS LOW AS -86C IN THE STRONGEST HOT TOWERS SURROUNDING THE EYE. 250950Z GPM 37GHZ AND 89GHZ MICROWAVE IMAGERY DEPICTED THE EYE TO GOOD EFFECT, SURROUNDED BY A SOLID BAND OF DEEP CONVECTION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE 19KM EYE IN THE EIR AND AN EXTRAPOLATION OF THE MICROWAVE EYE FEATURE. THE INITIAL INTENSITY IS ASSESSED WITH MEDIUM CONFIDENCE, PRIMARILY BASED ON FORECAST ASSESSMENT OF THE STRUCTURE AND APPEARANCE OF THE SYSTEM. THE APRF ESTIMATE OF T4.0 IS CLOSER TO REALITY BUT LIKELY TOO LOW AS IS THE PGTW T3.5 AND THE ADT WHICH IS MISSING THE PINHOLE EYE FEATURE ALTOGETHER. THE SYSTEM IS INTENSIFYING UNDER VERY FAVORABLE CONDITIONS WITH LOW SHEAR, VERY WARM, HIGH OHC WATERS AND A SMALL POINT SOURCE OVER TOP OF THE SYSTEM PROVIDING GOOD LOCALIZED RADIAL OUTFLOW AND A WEAK POLEWARD OUTFLOW CHANNEL.

MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE GUIDANCE HAS COME INTO A BIT BETTER AGREEMENT SINCE THE PREVIOUS FORECAST. UKMET AND GFS CONTINUE TO MARK THE EASTERN AND WESTERN BOUNDARIES RESPECTIVELY, WITH ALL TRACKERS SUPPORTING TO VARYING DEGREES THE SLOW, LOOPING MOTION FROM 24H TO 48H. THE JTWC FORECAST REMAINS CONSISTENT WITH THE PREVIOUS FORECAST, AND TRACKS THE CONSENSUS MEAN THROUGH 36H, THEN HEDGES TOWARDS THE WESTERN EDGE OF THE ENVELOPE THEREAFTER. DUE TO THE HIGH UNCERTAINTY ASSOCIATED WITH THE BINARY INTERACTION, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK. INTENSITY GUIDANCE IS MIXED, WITH THE HWRF AND COAMPS SUGGESTING NEAR-TERM WEAKENING TO 45 KNOTS FOLLOWED BY INTENSIFICATION AFTER MERGER TO A SECOND PEAK OF 95 KNOTS BY 96H. MEANWHILE THE DECAY SHIPS SUGGESTS STEADY INTENSIFICATION PEAKING AT AROUND 95 KNOTS. ADDITIONALLY THE RAPID INTENSIFICATION AIDS CONTINUE TO TRIGGER WITH THIS RUN, WITH RIPA PEAKING AT 125 KNOTS AT 48H. THE JTWC FORECAST FOLLOWS RIPA THROUGH 24H, BUT THEN SHIFTS TO ROUGHLY APPROXIMATE THE DECAY SHIPS AND HWRF SOLUTIONS THROUGH THE REMAINDER OF THE FORECAST. CONFIDENCE IS LOW IN LIGHT OF THE RAPID INTENSIFICATION TRENDS, POSSIBLE ERC AND THE ULTIMATE IMPACT OF THE BINARY INTERACTION AND MERGER.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TC 15S HAS STEADILY CONSOLIDATED AND INTENSIFIED OVER THE PAST DAY WHILE REMAINING QUASI-STATIONARY IN THE JOSEPH BONAPARTE GULF UNDER THE INFLUENCE OF A WEAK STEERING PATTERN. THE SYSTEM IS EXPECTED TO DRIFT GENERALLY SOUTHWESTWARD OVER THE NEXT 48 HOURS THOUGH THE EXACT TRACK IS UNCERTAIN AS THE STEERING REGIME IS EXPECTED TO REMAIN WEAK FOR THE NEXT COUPLE OF DAYS. AFTER 48H THE SUBTROPICAL RIDGE (STR) TO THE SOUTH IS FORECAST TO BUILD, WHICH WILL ALLOW FOR TC 15S TO MOVE OUT TOWARDS THE SOUTHWEST, STRADDLING THE KIMBERLY COAST THROUGH THE REMAINDER OF THE FORECAST PERIOD. THE EASTERLY SHEAR, CURRENTLY RUNNING AROUND 10-15 KNOTS IS EXPECTED TO RELAX SLIGHTLY, THOUGH TC 15S WILL CONTINUE TO STRUGGLE TO OVERCOME THIS SHEAR, LEADING TO SLOW BUT STEADY INTENSIFICATION TO A PEAK OF 50 KNOTS PRIOR TO LANDFALL NEAR CAPE LONDONDERRY. INCREASING SHEAR AND DISRUPTION OF THE LOW LEVEL CORE DUE TO LAND INTERACTION WITH WEAKEN THE SYSTEM AS IT TRANSITS ALONG THE COASTLINE THROUGH THE REMAINDER OF THE FORECAST. WHILE THE MAJORITY OF THE GUIDANCE SUPPORTS THE JTWC FORECAST, THE GFS AND GFS ENSEMBLE MEAN SUGGEST A WESTWARD TRACK OVER OPEN WATERS UNDER THE INFLUENCE OF A STRONGER STR TO THE SOUTH. THIS ALTERNATE SCENARIO WOULD ALLOW FOR A LONGER PERIOD OVER VERY WARM WATERS, WITH A HIGHER PEAK INTENSITY.

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.

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.