TC 13S(DJOUNGOU) from CAT 1 to CAT 3 in 24h: still intensifying// INVEST 95S up-graded//15P Subtropical//14P overland//1721utc

JTWC IS ISSUING 12HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 13S. 3HOURLY SATELLITE BULLETINS ARE ISSUED ON SUBTROPICAL 15P AND ON THE OVERLAND REMNANTS OF TC 14P.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS THAT THE VORTEX ASSOCIATED WITH TROPICAL CYCLONE (TC) 13S HAS UNDERGONE AXISYMMETRIZATION AND BECOME VERTICALLY ALIGNED, WITH A STRONG EYE EMERGING IN THE EIR WITHIN THE LAST 2 HOURS, MARKING THE ONSET OF FORECASTED PERIOD OF RAPID INTENSIFICATION (RI). A 171639Z TROPICS-6 91GHZ MICROWAVE IMAGER REVEALED A WELL-DEFINED MICROWAVE FEATURE, SURROUNDED BY MODERATELY STRONG DEEP CONVECTION, FORMING A SYMMETRICAL EYEWALL. A VERY SMALL AMOUNT OF VERTICAL TILT DOWNSHEAR TOWARDS THE SOUTH-SOUTHEAST IS EVIDENT IN THE HIGHER FREQUENCY TROPICS CHANNELS, CONFIRMING THE STRUCTURE SEEN IN THE HIGH-RESOLUTION MODEL FIELDS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE OBSERVABLE EYE IN THE INFRARED IMAGERY, AND EXTRAPOLATION OF THE MICROWAVE EYE IN THE TROPICS IMAGERY NOTED ABOVE. THE INITIAL INTENSITY OF 100 KTS IS PLACED WITH MEDIUM CONFIDENCE, CONSISTENT WITH SUBJECTIVE DVORAK ESTIMATES FROM 4.5 TO 5.5 (77-102 KTS) FROM MULTIPLE AGENCIES. ANALYSIS REVEALS A FAVORABLE ENVIRONMENT, WITH WARM SSTS, LOW DEEP-LAYER VWS AND ROBUST POLEWARD OUTFLOW INTO THE DIVERGENT ENTRANCE REGION OF A 130 KNOT JET MAX TO THE SOUTHEAST, WHICH IS THE MAIN FACTOR IN THE RAPID INTENSIFICATION OF THE SYSTEM.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 13S IS CURRENTLY TRACKING JUST A SHADE SOUTH OF DUE EAST, ALONG THE NER TO THE NORTH, WHICH EXTENDS ALL THE WAY TO AUSTRALIA. NO SIGNIFICANT CHANGE IN THE STEERING PATTERN IS EXPECTED, OTHER THAN A SLIGHT REORIENTATION OF THE RIDGE AXIS. THIS WILL PUSH TC 13S ONTO A MORE SOUTHEASTWARD TRACK AFTER TAU 12, WHICH WILL CONTINUE THROUGH THE REMAINDER OF THE FORECAST, AS THE SYSTEM TRACKS INTO THE MIDLATITUDES. THROUGH TAU 36, TC 13S IS FORECASTED TO CONTINUE TO RAPIDLY INTENSIFY, EXPECTED TO REACH A PEAK INTENSITY OF AT LEAST 120 KTS AT TAU 12. AFTER REACHING ITS PEAK, THE SYSTEM WILL BEGIN TO WEAKEN SLOWLY AT FIRST, BUT AFTER TAU 36 TC 13S WILL BEGIN TO RAPIDLY WEAKEN AS NORTHWESTERLY SHEAR INCREASES SHARPLY AND PULLS IN DRY AIR WHICH WILL ENTRAIN INTO THE CORE OF THE SYSTEM. TC 13S IS FORECASTED TO BEGIN SUBTROPICAL TRANSITION (STT) AT TAU 36 AND BY TAU 48, THE SYSTEM WILL BE DECAPITATED BY THE STRONG SHEAR AND SMOTHERED BY A DEEP LAYER OF DRY AIR ABOVE 700MB. STT IS FORECAST TO BE COMPLETE NO LATER THAN TAU 72, BUT POTENTIALLY AS EARLY AS TAU 48.

MODEL DISCUSSION: MODEL GUIDANCE CONTINUES TO BE IN TIGHT AGREEMENT DUE TO A VERY SIMPLE STEERING MECHANISM. THE JTWC TRACK FORECAST IS PLACED WITH HIGH CONFIDENCE WITH A CROSS-TRACK SPREAD AT TAU 72 OF JUST 100 NM. INTENSITY GUIDANCE HAS A BIT MORE SPREAD WITH MOST GUIDANCE SHOWING THE SAME GENERAL TREND THROUGHOUT THE FORECAST PERIOD. PEAK INTENSITY IN THE GUIDANCE RANGES FROM 110 KNOTS FOR THE SHIPS MODEL, UP TO 135 KNOTS FOR THE COAMPS-TC ENSEMBLE MEAN (CTR1) WITH THE JTWC FORECAST MOST CLOSELY FOLLOWING THE HAFS-A GUIDANCE THROUGH TAU 36. FOR THE REMAINDER OF THE FORECAST PERIOD, THE GUIDANCE PACKAGE IS IN GOOD AGREEMENT WITH WEAKENING AFTER TAU 24, BUT WITH A 20 KT SPREAD THROUGH TO THE END OF FORECAST PERIOD. FOR THIS REASON, THE JTWC INTENSITY FORECAST IS PLACED WITH MEDIUM CONFIDENCE.

AN AREA OF CONVECTION (INVEST 95S) HAS PERSISTED NEAR 17.9S 51.8E, APPROXIMATELY 356 NM WEST-NORTHWEST OF MAURITIUS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY AND A 171501Z SSMIS 91GHZ MICROWAVE IMAGE DEPICT A QUICKLY CONSOLIDATING LOW LEVEL CIRCULATION (LLC) WITH A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) THAT HAS FRAGMENTED BANDING FORMING ON THE NORTHERN AND SOUTHERN PERIPHERIES OF THE SYSTEM. THE ENVIRONMENT IS HIGHLY FAVORABLE FOR FURTHER DEVELOPMENT WITH LOW (5-10KT) VWS, GOOD POLEWARD OUTFLOW ALOFT, AND WARM (29-30 C) SST. GLOBAL MODELS ARE IN AGREEMENT THAT INVEST 95S WILL CONTINUE ON A NORTHEASTWARD TRACK WITH STEADY INTENSIFICATION OVER THE NEXT 36-48 HOURS. AFTER NESTLING OVER A PATCH OF INVIGORATING 32C SST, 95S WILL QUICKLY TURN EASTWARD THEN PERFORM A POSSIBLE MOONWALK AND TURN SOUTHWARD TOWARDS THE MASCARENE ISLANDS, WHILE RAPIDLY INTENSIFYING. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 17 TO 22 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1006 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO MEDIUM.

GLOBAL MODELS ARE IN AGREEMENT THAT INVEST 95S WILL CONTINUE ON A NORTHEASTWARD TRACK WITH STEADY INTENSIFICATION OVER THE NEXT 36-48 HOURS. AFTER NESTLING OVER A PATCH OF INVIGORATING 32C SST, 95S WILL QUICKLY TURN EASTWARD THEN PERFORM A POSSIBLE MOONWALK AND TURN SOUTHWARD TOWARDS THE MASCARENE ISLANDS, WHILE RAPIDLY INTENSIFYING.

AN AREA OF CONVECTION (REMNANTS 15P) HAS PERSISTED NEAR 29.3S 152.5W, APPROXIMATELY 778 NM SOUTH OF BORA BORA. THE SYSTEM IS CURRENTLY CLASSIFIED AS A SUBTROPICAL CYCLONE, GENERALLY CHARACTERIZED AS HAVING BOTH TROPICAL AND MIDLATITUDE CYCLONE FEATURES. ANIMATED EIR SATELLITE IMAGERY AND A 171049Z AMSR2 89GHZ SATELLITE MICROWAVE IMAGE DEPICTS A FULLY EXPOSED LOW LEVEL CIRCULATION CENTER WITH ASSOCIATED CONVECTION OFFSET TO THE SOUTHEAST. ENVIRONMENTAL ANALYSIS REVEALS UNFAVORABLE CONDITIONS FOR TROPICAL TRANSITION DEFINED BY A DEEP LAYER OF DRY AIR BEING ADVECTED OVER THE CIRCULATION, STRONG WESTERLIES ALOFT, HIGH (30KT) VERTICAL WIND SHEAR, AND COOL (25-26C) SEA SURFACE TEMPERATURES. GLOBAL MODELS ARE IN AGREEMENT THAT THE REMNANTS OF TC 15P WILL TRACK SOUTHEASTWARD WITH A BROAD AND ASYMMETRIC WIND FIELD. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 42 TO 48 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 989 MB. 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 DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS LOW.

GLOBAL MODELS ARE IN AGREEMENT THAT THE REMNANTS OF TC 15P WILL TRACK SOUTHEASTWARD WITH A BROAD AND ASYMMETRIC WIND FIELD.