TC 13S(DJOUNGOU) former Super Typhoon now rapidly decaying//TC 16S developing next 72h//10 Day ECMWF Storm Tracks//1910utc

JTWC IS ISSUING 12HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 13S AND ON TC 16S. 3HOURLY SATELLITE BULLETINS ARE ISSUED ON THE OVERLAND REMNANTS OF TC 14P.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS TROPICAL CYCLONE (TC) 13S (DJOUNGOU) EXHIBITING A RAPIDLY DETERIORATING STRUCTURE DUE TO THE INFLUENCE OF VERY STRONG (35-40 KTS) VERTICAL WIND SHEAR AND DRY AIR ENTRAINMENT OVER THE PAST TWELVE HOURS. DEEP CONVECTION PERSISTS SOUTHEAST OF THE LLCC, SHOWING THE TC VORTEX TO BE TILTED BUT STILL PROVIDING NECESSARY OUTFLOW. ENVIRONMENTAL ANALYSIS SHOWS THE TC HAS CROSSED THE 26C ISOTHERM, REMOVING NECESSARY WARM WATER INTAKE AT THE SURFACE. WITH MARGINALLY FAVORABLE DIVERGENCE BEING THE ONLY SUPPORTING ENVIRONMENTAL FACTOR FOR SUSTAINMENT, THE ENVIRONMENT IS ASSESSED AS UNFAVORABLE OVERALL. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 190600Z GEOSTATIONARY VISIBLE SATELLITE IMAGE SHOWING A MOSTLY EXPOSED LOW LEVEL CIRCULATION CENTER. THE INITIAL INTENSITY OF 90 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON THE SUBJECTIVE AND OBJECTIVE INTENSITY ESTIMATES LISTED BELOW.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 13P IS FORECAST TO TRACK GENERALLY EAST-SOUTHEASTWARD FROM TAU 00 TO TAU 36, FOLLOWING THE STEERING INFLUENCE OF A DEEP-LAYER SUBTROPICAL RIDGE ANCHORED OVER WEST-CENTRAL AUSTRALIA. WITH THE AFOREMENTIONED UNFAVORABLE ENVIRONMENT IN PLAY, INTENSITY IS FORECAST TO RAPIDLY FALL AS THE SYSTEM TRANSITIONS TO A SUBTROPICAL BY TAU 12, BECOMING EXTRATROPICAL PRIOR TO TAU 36. A MODERATE TEMPERATURE GRADIENT AND ELONGATION OF THE LLCC ALLUDE THE SUBTROPICAL TRANSITION HAS COMMENCED. NEAR TAU 12, NUMERICAL MODELS AND STATISTICAL-DYNAMICAL GUIDANCE SUGGEST DIVERGENCE ALOFT SHARPLY AND SIGNIFICANTLY DECLINES, REMOVING THE LAST FAVORABLE ENVIRONMENTAL ELEMENT SUPPORTING SUSTAINMENT OF THE SYSTEM.

MODEL DISCUSSION: GLOBAL NUMERICAL MODEL GUIDANCE IS IN EXCEPTIONAL AGREEMENT REGARDING BOTH TRACK AND INTENSITY THROUGHOUT THE FORECAST INTERVAL (TAU 00 TO TAU 36). A CROSS-TRACK SPREAD OF 119NM (TAU 36) AND INTENSITY SPREAD OF 15KTS (TAU 36) CONTRIBUTE TO THE OVERALL FORECAST CONFIDENCE OF HIGH. ALL GUIDANCE SUPPORTS A RAPID DOWNTREND IN INTENSITY THROUGHOUT THE FORECAST INTERVAL AS THE SYSTEM TRACKS EAST-SOUTHEASTWARD.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TC 16S FORECAST TO TRACK GENERALLY EASTWARD ALONG THE SOUTHERN SIDE OF THE STRONG NER TO THE NORTH THROUGH THE FIRST 24 HOURS OF THE FORECAST. AFTER TAU 24, THE NER BEGINS TO BREAK DOWN TO THE NORTH OF THE SYSTEM, GENERATING A WEAKNESS IN THE STEERING GRADIENT. BY TAU 36, A MIGRATORY RIDGE PASSING FAR TO THE SOUTH WILL BUILD TOWARDS THE NORTHEAST, ULTIMATELY MERGING WITH AN EASTERN LOBE OF THE NER CENTERED NEAR 10S 75E, GENERATING A SOLID WALL OF RIDGING EXTENDING ALONG A SOUTHWEST-NORTHEAST AXIS FROM 10S TO 30S. TC 16S WILL NOT HAVE THE JUICE TO PUSH INTO THIS DEEP RIDGING AND INSTEAD WILL TAKE THE PATH OF LEAST RESISTANCE, AND TURN SHARPLY SOUTHWARD BETWEEN TAUS 36 AND 48. TC 16S THEN TRACKS SOUTH-SOUTHWESTWARD THROUGH TAU 96, GENERALLY TOWARDS THE MASCARENE ISLANDS, ALONG THE WEST SIDE OF A COMPLEX RIDGE PATTERN THAT DEVELOPS IN THE CENTRAL INDIAN OCEAN. BY THE END OF THE FORECAST PERIOD, A TROUGH PASSING BY TO THE SOUTH WILL ERODE THE STEERING RIDGE AND WEAKEN THE GRADIENT, LEADING TO A SLOW-DOWN IN TRACK SPEED AND A TURN MORE WESTWARD BY TAU 120. IN TERMS OF INTENSITY, THE SYSTEM WILL TAKE ADVANTAGE OF THE FAVORABLE ENVIRONMENT, BUT WILL BE RELATIVELY SLOW TO INTENSIFY FOR THE FIRST 24 HOURS AS IT CONTINUES TO CONSOLIDATE THE VORTEX. ONCE THE VORTEX IS FIRMLY ESTABLISHED, THE FORECAST CALLS FOR A MORE RAPID PACE OF INTENSIFICATION AS IT PASSES OVER VERY WARM WATERS WITH RELATIVELY HIGH OHC VALUES, AND UPPER-LEVEL OUTFLOW INCREASES. A PEAK OF 85 KNOTS IS EXPECTED BY TAU 72 BEFORE CONDITIONS BEGIN TO DETERIORATE. REDUCED OUTFLOW ACCOMPANIED BY INCREASED SHEAR AND DRY AIR ENTRAINMENT BEGIN TO TAKE THEIR TOLL AFTER TAU 72, AND TC 16S WILL STEADILY WEAKEN THROUGH THE REMAINDER OF THE FORECAST.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE SHOWS A WIDE SPREAD IN POTENTIAL TRACK SOLUTIONS, PARTICULARLY AFTER TAU 36 WHEN THE SYSTEM BEGINS TO TURN SOUTHWARD. ACROSS THE CONSENSUS MEMBERS, THE TRIO OF THE UKMET BASED MODELS INCLUDING UKMET ENSEMBLE, EGRR AND THE GALWEM ALL DISPLAY THE SAME GENERAL TRACK TYPE AS THE REST OF THE GUIDANCE BUT TRACK THE SYSTEM EAST OF PORT MATHURIN. THIS SERVES TO PULL THE CONSENSUS MEAN SIGNIFICANTLY TOO FAR TO THE EAST. THE REMAINDER OF THE GUIDANCE PACKAGE LIES IN A MORE TIGHTLY-PACKED ENVELOPE THAT GRADUALLY EXPANDS FROM 100NM AT TAU 48 TO 320NM BY TAU 120, WITH ALL THE MEMBERS CONFINED TO THE WEST OF THE CONSENSUS MEAN. A MANUAL RUN OF A NEW CONSENSUS WHICH DISCARDS THE OUTLIERS ABOVE GENERATES A MORE REALISTIC SCENARIO, WITH THE TRACK PASSING JUST EAST OF MAURITIUS. THE JTWC FORECAST CLOSELY TRACKS THIS MANUAL CONSENSUS MEAN AND THE ECMWF TRACKER. CONFIDENCE IS LOW HOWEVER, PARTICULARLY AFTER TAU 48 DUE TO VERY LARGE MODEL SPREAD. BOTH THE GEFS AND ECENS ENSEMBLES ALSO SHOW A HIGH AMOUNT OF SPREAD, LENDING EVEN MORE UNCERTAINTY IN THE FORECAST. INTENSITY GUIDANCE IS MIXED AS WELL, WITH THE GLOBAL-MODEL-BASED SHIPS GUIDANCE, THE COAMPS-TC (NAVGEM) AND THE HWRF MODELS SHOWING FAR MORE EXCITEMENT THAN THE OTHER MESOSCALE MODELS SUCH AS HAFS-A AND THE GFS-BASED COAMPS-TC. THE LATTER MODELS ONLY SHOW MODEST INTENSIFICATION TO A PEAK BETWEEN 50-65 KNOTS, WHILE THE FIRST MODELS SHOW A PEAK CLOSER TO 95 KNOTS. ALL AGREE THAT THE PEAK WILL BE AT TAU 72, FOLLOWED BY A STEADY WEAKENING THROUGH TAU 120. THE JTWC FORECAST GENERALLY FOLLOWS ABOUT 5 KNOTS LOWER THAN THE SHIPS GUIDANCE AND SIGNIFICANTLY LOWER THAN THE RAPID INTENSIFICATION AIDS WHICH ARE TRIGGERING WITH THIS MODEL RUN. CONFIDENCE IS LOW THROUGH THE FORECAST PERIOD.