Active South Indian Ocean: TC 21S(CHARLOTTE) weakening// TC 22S(HALIMA): Cat 2 US by 48h, maybe higher,23/15utc

JTWC IS ISSUING 6HOURLY WARNINGS ON TC 21S(CHARLOTTE) AND 12HOURLY WARNINGS ON TC 22S(HALIMA). 3HOURLY SATELLITE BULLETINS ARE ISSUED FOR BOTH SYSTEMS. THEY WERE DISCONTINUED FOR INVEST 91B AT 23/0540UTC.

23/1510UTC.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC CHARLOTTE WILL CONTINUE SOUTHWESTWARD UNDER THE STEERING INFLUENCE OF THE SUBTROPICAL RIDGE (STR). AFTER 24H, IT WILL ROUND THE STR AXIS AND TRACK MORE SOUTHWARD THEN SOUTHEASTWARD ON THE POLEWARD SIDE OF THE STR. THE ENVIRONMENT IS EXPECTED TO BECOME MORE UNFAVORABLE WITH INCREASING VWS, INFLUX OF LOW LEVEL DRY AIR, AND COOLING SST, CONTINUING THE GRADUAL DETERIORATION. CONCURRENTLY BY 48H, THE SYSTEM WILL BEGIN SUBTROPICAL TRANSITION AND BY 72H WILL TRANSFORM INTO A GALE-FORCE, 40-KNOT SUBTROPICAL SYSTEM WITH AN EXPANDING WIND FIELD.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A WEAKENING SYSTEM AS EVIDENCED BY A WARMING CENTRAL CONVECTION AND UNRAVELING FEEDER BANDS. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON EXPOSED, RAGGED, ALBEIT DEFINED LOW LEVEL CIRCULATION FEATURES IN THE 231058Z AND 230926Z SSMIS 91GHZ MICROWAVE IMAGES. THE INITIAL INTENSITY OF 65KTS IS BASED WITH MEDIUM CONFIDENCE ON THE HIGH END OF AGENCY AND AUTOMATED DVORAK ESTIMATES (SEE BELOW). ANALYSIS INDICATES AN UNFAVORABLE ENVIRONMENT WITH STRONG POLEWARD OUTFLOW AND WARM SST OFFSET BY MODERATE TO STRONG WESTERLY VWS. THE CYCLONE IS TRACKING ALONG THE NORTHWEST PERIPHERY OF THE DEEP LAYER STR TO THE SOUTHEAST.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT UP TO 48H; AFTERWARD, THEY ERRATICALLY SPREAD OUT WITH THE MAJORITY INDICATING A REVERSAL IN THE STORM MOTION IN VARIOUS TRAJECTORIES. IN VIEW OF THIS, THERE IS ONLY MEDIUM CONFIDENCE IN THE JTWC TRACK FORECAST THAT IS LAID CLOSE TO THE MODEL CONSENSUS.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TC HALIMA WILL CONTINUE ON A SOUTHWESTWARD TRACK UNDER THE STR TO THE SOUTHEAST UP TO 24H. AFTERWARD, IT WILL BEGIN TO ROUND THE STR AXIS AND TRACK MORE SOUTHWARD, THEN BY 72H, SOUTHEASTWARD. THE FAVORABLE CONDITIONS WILL CARRY THROUGH 48H AND FUEL A GRADUAL THEN RAPID INTENSIFICATION TO A PEAK OF 85KTS/CAT 2 US, POSSIBLY HIGHER. AFTER 48H, INCREASING VWS AND COOLING SST WILL GRADUALLY ERODE THE SYSTEM DOWN TO 60KTS BY 120H.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A MEDIUM-SIZED, ELONGATED, AND CONSOLIDATING SYSTEM WITH DISORGANIZED AND FRAGMENTED FORMATIVE BANDS FEEDING INTO A DEEPENING CENTRAL CONVECTION THAT IS OBSCURING THE LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE RAGGED BUT DEFINED LLC FEATURE IN THE 230857Z AMSR2 89GHZ IMAGE. THE INITIAL INTENSITY OF 35KTS IS BASED WITH MEDIUM CONFIDENCE ON THE FMEE DVORAK ESTIMATE OF T2.5 AND FROM THE 230855Z GCOMW1.AMSR2.WINDSPEED DATA SHOWING A 37KT PIXEL. ANALYSIS INDICATES A FAVORABLE ENVIRONMENT WITH LOW VWS, STRONG POLEWARD OUTFLOW, AND WARM ALONG-TRACK SST. THE CYCLONE IS TRACKING ALONG THE NORTHWEST PERIPHERY OF THE STR TO THE SOUTHEAST.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT WITH A GRADUAL AND EVEN SPREAD TO 380KM BY 72H. AFTERWARD THE MODELS SIGNIFICANTLY DIVERGE WITH THE MAJORITY INDICATING A REVERSAL IN STORM MOTION. IN VIEW OF THIS, THERE IS MEDIUM CONFIDENCE IN THE JTWC TRACK AND INTENSITY FORECASTS UP TO 72H THEN LOW CONFIDENCE AFTERWARD.