TC 05S is forecast to intensify significantly next 72h and dangerously approach REUNION and MAURITIUS islands//1215utc

JTWC IS ISSUING 12HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 05S.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A RAPIDLY CONSOLIDATING AND INTENSIFYING SYSTEM, WITH WELL-DEFINED SPIRAL BANDS WRAPPING INTO AN INCREASINGLY DEFINED LOW LEVEL CIRCULATION CENTER (LLCC). WHILE CLOUD TOP TEMPERATURES HAVE WARMED OVER THE PAST THREE HOURS, DEEP CONVECTIVE TOWERS CONTINUE TO FIRE ON THE NORTHERN SIDE OF THE CENTER BUT ARE STRUGGLING TO WRAP UPSHEAR. A 121011Z AMSR2 36GHZ MICROWAVE IMAGE DEPICTS A SMALL, WELL-DEFINED INNER CORE OF MODERATE CONVECTION, WITH STRONG INFLOW BANDS TO THE WEST-SOUTHWEST AND NORTHERN SIDES OF THE LLCC AND A WEAK LOW EMISSIVITY REGION (LER) DEFINING THE CIRCULATION CENTER. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON AN EXTRAPOLATION OF THE DEVELOPING LER IN THE AMSR2 IMAGE AND A DIMPLE FEATURE IN THE ANIMATED MSI. THE INITIAL INTENSITY OF 35 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE DRAMATICALLY IMPROVED STRUCTURE AND THE T2.5 DVORAK CURRENT INTENSITY ESTIMATES FROM BOTH PGTW AND DEMS. ANALYSIS REVEALS A VERY FAVORABLE ENVIRONMENT CHARACTERIZED BY LOW (0-5 KNOTS) OF EASTERLY SHEAR, DUAL-CHANNEL OUTFLOW ALOFT, ZESTY SSTS AND HIGH OHC OVER 100 KJ PER CM3. THE SYSTEM IS MOVING TO THE SOUTHWEST ALONG THE WESTERN SIDE OF A SUBTROPICAL RIDGE (STR) CENTERED TO THE EAST.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 05S (FIVE) IS FORECAST TO TRACK GENERALLY TOWARDS THE SOUTHWEST ALONG THE WEST SIDE OF THE STEERING RIDGE FOR THE NEXT 36 HOURS. TRACK SPEEDS WILL REMAIN RELATIVELY STEADY THROUGH THE FIRST DAY OR SO OF THE FORECAST AS THE RIDGE REMAINS ENTRENCHED TO THE EAST. BY TAU 36, THE TRACK BEGINS TO TURN MORE SOUTHWARD AND SLOWS DOWN AS THE RIDGE BEGINS TO REORIENT TO A MORE NORTHWEST-SOUTHEAST AXIS. SHORTLY AFTER TAU 48, TC 05S WILL BE FIRMLY SET UPON A SOUTHEASTWARD TRACK AS THE RIDGE COMPLETES IS REORIENTATION PHASE, AND IS EXPECTED TO PASS BETWEEN LA REUNION AND MAURITIUS AROUND TAU 96, THEN CONTINUE INTO THE OPEN WATERS OF THE SOUTHERN INDIAN OCEAN. IN TERMS OF INTENSITY, THE ENVIRONMENT IS OPTIMUM FOR RAPID INTENSIFICATION ONCE THE LLCC FULLY CONSOLIDATES, WHICH IS EXPECTED IMMINENTLY. OPTIMUM CONDITIONS ARE FORECAST TO CONTINUE FOR THE NEXT 48 HOURS, ALLOWING THE SYSTEM TO INTENSIFY AT LEAST 60 KNOTS IN THE NEXT TWO DAYS. CONDITIONS REMAIN FAVORABLE FOR ANOTHER 24 HOURS AFTER THAT, AND ADDITIONAL INTENSIFICATION UP TO AT LEAST 105 KNOTS, AND POTENTIAL HIGHER, IS EXPECTED PRIOR TO THE SYSTEM REACHING THE MASCARENE ARCHIPELAGO. A RAPID DECREASE IN OCEAN HEAT CONTENT AND SSTS, ACCOMPANIED BY A SHARP INCREASE IN SHEAR WILL INDUCE A SLOW BUT STEADY WEAKENING TREND AFTER TAU 96 AS THE SYSTEM CONTINUES MOVING POLEWARD.

MODEL DISCUSSION: DETERMINISTIC TRACK GUIDANCE IS IN GOOD OVERALL AGREEMENT, WITH THE NOTABLE EXCEPTION OF NAVGEM, THROUGH THE FIRST 72 HOURS OF THE FORECAST. ALL OF THE GUIDANCE EXCEPT NAVGEM, WHICH IS FAR TO THE EAST, IS CONFINED TO A 105NM ENVELOPE THROUGH TAU 72. HOWEVER, THE NAVGEM IS PULLING THE CONSENSUS MEAN EASTWARD SUCH THAT IT MARKS THE RIGHT SIDE OF THE MODEL ENVELOPE, WITH THE REMAINDER OF THE CONSENSUS MEMBERS TO THE LEFT, OR WEST, OF THE MEAN THROUGH TAU 72 WHILE THE ECMWF INTERMEDIATE FORECAST MARKS THE WESTERN SIDE OF THE ENVELOPE, AND TRACKS THE SYSTEM OVER LA REUNION. THE JTWC FORECAST LIES WEST OF THE CONSENSUS MEAN AND CONSISTENT WITH THE GFS TRACKER THROUGH TAU 72 WITH MEDIUM CONFIDENCE. AFTER TAU 72, THE GUIDANCE BEGINS TO SPREAD OUT, PARTICULARLY IN THE ALONG-TRACK DIRECTION, WITH SPREAD INCREASING TO AT LEAST 350NM BETWEEN THE ECMWF AND THE GALWEM TRACKERS. THE JTWC FORECAST REMAINS JUST WEST AND SOUTH OF THE CONSENSUS MEAN THROUGH TAU 120, WITH MEDIUM CONFIDENCE. INTENSITY GUIDANCE IS IN GOOD AGREEMENT THAT THE SYSTEM WILL RAPIDLY INTENSIFY (RI), WITH MULTIPLE RI AIDS TRIGGERING. ADDITIONALLY, THE COAMPS-TC ENSEMBLE RI PROBABILITIES ARE SET AT 95 PERCENT THROUGH TAU 60, PROVIDING HIGH CONFIDENCE TO THE FORECAST THROUGH TAU 48. ALL MEMBERS OF THE CONSENSUS AGREE ON A LEVELING OFF OF THE INTENSITY AFTER TAU 72, FOLLOWED BY A STEADY WEAKENING PHASE THROUGH THE END OF THE FORECAST PERIOD. THE JTWC FORECAST TRACKS ABOVE MOST OF THE GUIDANCE, CLOSE THE MOST AGGRESSIVE RI GUIDANCE, THROUGH TAU 48, THEN CLOSELY TRACKS THE CONSENSUS MEAN THEREAFTER.