TC 18S struggling but forecast to intensify a bit after 24h// TC 19P to intensify over the GOC next 36/48h// 15/21UTC

JTWC IS ISSUING 6HOURLY WARNINGS AND 12HOURLY SATELLITE BULLETINS ON TC 18S AND ON TC 19P

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 18S IS CURRENTLY TRACKING WEST-SOUTHWESTWARD ALONG THE NORTHWESTERN PERIPHERY OF THE STR LOCATED OVER CENTRAL AUSTRALIA AND EXTENDING WESTWARD INTO THE SOUTHWESTERN INDIAN OCEAN (IO). AS THE AFOREMENTIONED DEEP-LAYER STR CONTINUES TO BUILD SLIGHTLY WESTWARD, TC 18S IS FORECASTED TO CONTINUE ITS SLOW, MEANDERING WEST- SOUTHWESTWARD TRACK THROUGH TAU 36. AFTER TAU 36, A DEEP LONGWAVE TROUGH WILL WEAKEN THE STR STEERING FLOW, ALLOWING FOR A SHARP SOUTHWESTWARD TRACK UNTIL TAU 72. AS THE HIGH IN THE SOUTHERN IO REORIENTS EASTWARD, TC 18S WILL BEGIN A WEST-NORTHWESTWARD TRACK ALONG THE NORTHERN PERIPHERY OF THE SOUTHEAST TRADE FLOW THROUGH TAU 120. AS THE CYCLONE PROGRESSES GENERALLY WESTWARD, A MORE CONDUCIVE ENVIRONMENT IS EXPECTED AS VERTICAL WIND SHEAR (VWS) REMAINS LOW (10- 15 KNOTS), THE SYSTEM'S CORE MAINTAINS ITS MOIST STRUCTURE, AND FAVORABLE POLEWARD OUTFLOW INCREASES, RESULTING IN A STEADY INCREASE IN INTENSITY THROUGH TAU 120 OF UP TO 65 KNOTS.

MODEL DISCUSSION: THE DETERMINISTIC MODEL TRACK GUIDANCE IS IN POOR AGREEMENT THROUGH TAU 72, AS THE NAVGEM AND GFS TRACKERS HAVE ILLUSTRATED ERRATIC FORECAST SOLUTIONS OVER THE LAST 12 HOURS AWAY FROM THE CONSENSUS. THE 150600Z ECMWF ENSEMBLE (EPS) AND GFS ENSEMBLE (GEFS) ALSO INDICATE CONTINUED UNCERTAINTY AFTER TAU 72 DUE TO COMPETING STEERING MECHANISMS, WITH TWO DISTINCT GROUPINGS OF SOLUTIONS IN A SOUTHWARD AND WESTWARD TRAJECTORY. ROUGHLY 90 PERCENT OF THE EPS AND GEFS SOLUTIONS DEPICT A GENERAL WESTWARD TRACK, WHILE 10 PERCENT OF ENSEMBLE SOLUTIONS HAVE SHOWN A SLOW SOUTHWARD TRACK INTO NORTHWESTERN AUSTRALIA. THE 150600Z COAMPS-TC INTENSITY ENSEMBLE (CTCXEPS) SHOWS A STEADY INTENSIFICATION TREND, WITH DECREASING PEAK PROBABILITIES REACHING MODERATE INTENSIFICATION OF 30 TO 40 PERCENT BETWEEN TAU 60 AND TAU 84.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THIS INITIAL PROGNOSTIC REASONING MESSAGE ESTABLISHES THE FORECAST PHILOSOPHY. FORECAST DISCUSSION: TROPICAL CYCLONE (TC) 19P IS FORECAST TO TRACK GENERALLY SOUTHWARD ALONG THE WESTERN PERIPHERY OF THE NORTH-SOUTH ORIENTED STR POSITIONED TO THE EAST THROUGH TAU 48. TC 19P WILL INTENSIFY QUICKLY AS IT TRACKS AWAY FROM LAND WITH A PEAK INTENSITY OF 65 KNOTS EXPECTED FROM TAU 36 TO TAU 48. AFTER TAU 48, THE SYSTEM WILL TRANSITION STEERING TO A SUBTROPICAL RIDGE POSITIONED SOUTH OF THE SYSTEM AND WILL TURN WESTWARD, MAKING LANDFALL NEAR TAU 72. RAPID WEAKENING WILL OCCUR AS THE SYSTEM TRACKS INLAND, WITH DISSIPATION EXPECTED BY TAU 96.

MODEL DISCUSSION: WITH THE EXCEPTION OF NAVGEM, NUMERICAL MODEL GUIDANCE IS FAIR AGREEMENT THROUGH THE FORECAST PERIOD, LENDING MEDIUM OVERALL CONFIDENCE TO THE JTWC TRACK FORECAST. THE 150600Z ECMWF AND GFS ENSEMBLES (EPS AND GEFS) ALSO SUPPORT THE JTWC TRACK FORECAST. RELIABLE INTENSITY GUIDANCE SUPPORTS THE SHARP INTENSIFICATION TREND THROUGH TAU 36 AND ALSO THE RAPID WEAKENING PHASE AFTER TAU 72 WITH MEDIUM OVERALL CONFIDENCE. ALTHOUGH THE 150600Z COAMPS-TC INTENSITY PROBABILITY GUIDANCE DOES NOT INDICATE RAPID INTENSIFICATION, IT DOES SHOW 40 TO 60 PERCENT PROBABILITIES FOR MODERATE INTENSIFICATION THROUGH TAU 36.