TC 20S intensifying next 72H and to curve to the SouthEast after 48H// 2603utc

JTWC IS ISSUING 12HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 20S

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS TROPICAL CYCLONE 20S NEARLY QUASI-STATIONARY (QS) IN A COMPETING STEERING ENVIRONMENT CAUGHT AT A NEAR STANDSTILL BETWEEN A NEAR EQUATORIAL RIDGE (NER) TO THE EAST, WEST, AND NORTH. PERSISTENT CONVECTION IS BEGINNING TO CONSOLIDATE INTO AN UPPER-LEVEL MICROWAVE EYE-LIKE STRUCTURE THAT WAS DEPICTED ON A 252147Z ATMS IMAGE. HOWEVER, THE LOW-LEVEL IS COMPLETELY OBSCURED AND UNABLE TO BE IDENTIFIED. ON THE UPPER-LEVEL, AN ANTICYCLONE HAS DEVELOPED OVER THE SYSTEM WITH THE SUBTROPICAL JET TO THE SOUTH ENCOURAGING A STRONG POLEWARD OUTFLOW CHANNEL. MINIMAL VERTICAL WIND SHEAR (VWS) OF 5-10KTS AND SEA SURFACE TEMPERATURES OF 29-30C CREATE A POSITIVELY FAVORABLE ENVIRONMENT FOR INTENSIFICATION. THE INITIAL POSITION WAS ASSESSED WITH LOW CONFIDENCE BASED ON AN EXTRAPOLATION FROM THE PREVIOUSLY MENTIONED ATMS IMAGE AND ANIMATED EIR IMAGERY. THE INITIAL INTENSITY WAS ASSESSED WITH LOW CONFIDENCE BASED ON AGENCY AND OBJECTIVE FIXES LISTED BELOW.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TC 20S IS FORECAST TO REMAIN QS FOR THE NEXT 12 HOURS BEFORE BEGINNING TO SLOWLY CURVE TO THE SOUTH-SOUTHWEST AS IT ROUNDS THE WESTERN PERIPHERY OF THE NER TO THE EAST. FROM TAU 48-120, THE SYSTEM BEGINS TO CHANGE DIRECTION TO THE SOUTHEAST ON THE WESTERN PERIPHERY OF THE NER WHICH GRADUALLY MOVES EAST. AS THE SYSTEM TRAVELS SOUTH, IT IS EXPECTED TO BEGIN SUBTROPICAL TRANSITION AT TAU 120 DUE TO COOLER SSTS, INCREASED VWS, AND CLOSE PROXIMITY TO THE JET MAXIMUM. IN THE INTENSITY FORECAST, THERE IS A MODERATE LIKELIHOOD OF RAPID INTENSIFICATION (RI) TO 95KTS BETWEEN TAU 60-72 DUE TO CONSISTENTLY LOW VWS, STRONG DIVERGENCE ALOFT, AND FAVORABLE SSTS THROUGH TAU 60. THE PRIMARY MITIGATING FACTOR TO EVEN MORE SIGNIFICANT INTENSIFICATION IS THE PROXIMITY TO LAND OVER THE FIRST 36 HOURS, WHICH HAS THE POTENTIAL TO INTRODUCE DRY AIR FROM THE MOUNTAINOUS TERRAIN OF NORTHERN MADAGASCAR AND FRICTION FROM TOPOGRAPHY. AN INCREASE IN VWS TO 20-25KTS FROM TAU 72-120 IS EXPECTED TO CAUSE THE VORTEX TO SHALLOW AND BECOME EMBEDDED INTO A JET MAXIMUM AS THE SYSTEM TRAVELS SOUTH, DRASTICALLY REDUCING OUTFLOW AND ALLOWING FOR THE SYSTEM TO WEAKEN GRADUALLY.

MODEL DISCUSSION: DETERMINISTIC MODEL GUIDANCE IS IN GOOD AGREEMENT IN THE NEAR TERM BUT CROSS-TRACK SPREAD BEGINS TO OPEN TO 250NM BY TAU 96. THERE BEGINS TO BE DEVIATIONS IN THE TRACK SPEED AT THAT SAME TIME, WITH GFS INCREASING TRACK SPEED RAPIDLY AND UKMET TAKING A MUCH SLOWER PATH LIKELY DUE TO DISAGREEMENT IN HOW SIGNIFICANTLY THE VORTEX WILL BE SHEARED AND SHALLOW BY THE END OF THE FORECAST PERIOD. THE INTENSITY GUIDANCE HAS A LARGE SPREAD BUT GENERALLY FORECASTS A PEAK BETWEEN 80-100KTS AT TAU 48. THE JTWC FORECAST PREDICTS A PEAK OF 95KTS BETWEEN TAU 60-72 DUE TO FAVORABLE OUTFLOW, SSTS, AND VWS. POTENTIAL INTERACTION FROM LAND ALSO WAS TAKEN INTO ACCOUNT EXPECTING THAT THE PEAK WILL OCCUR ONCE TC 20S MOVES AWAY FROM THE COAST OF MADAGASCAR.

THERE IS A MODERATE LIKELIHOOD OF RAPID INTENSIFICATION (RI) TO 95KTS BETWEEN TAU 60-72 DUE TO CONSISTENTLY LOW VWS, STRONG DIVERGENCE ALOFT, AND FAVORABLE SSTS THROUGH TAU 60.

ON THE UPPER-LEVEL, AN ANTICYCLONE HAS DEVELOPED OVER THE SYSTEM WITH THE SUBTROPICAL JET TO THE SOUTH ENCOURAGING A STRONG POLEWARD OUTFLOW CHANNEL.