TC 18S forecast to peak as a powerful CAT 4 US in 96h just before landfall East of Port Hedland//Invest 90W up-graded// 0906utc

JTWC IS ISSUING 6HOURLY WARNINGS ON TC 18S. 3HOURLY SATELLITE BULLETINS ARE ISSUED ON TC 18S AND INVEST 90W.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A CONSOLIDATING SYSTEM WITH EXPANSIVE SPIRAL BANDING FROM ALL QUADRANTS BEGINNING TO TAKE SHAPE AND FEEDING INTO THE COLD DENSE OVERCAST THAT IS OBSCURING THE LOW LEVEL CIRCULATION (LLC). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM LOW CLOUD LINES WRAPPING TOWARD THE LLC. THE INITIAL INTENSITY IS BASED WITH HIGH CONFIDENCE FROM THE AUTOMATED DVORAK ESTIMATE AND CONSISTENT WITH THE IMPROVEMENT IN THE EIR CONVECTIVE SIGNATURE OVER THE PAST SIX HOURS. TC 18S IS IN A FAVORABLE ENVIRONMENT WITH LIGHT-MODERATE VWS, STRONG POLEWARD OUTFLOW AND VERY WARM ALONG-TRACK SST.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 18S WILL CONTINUE TO TRACK SOUTHWESTWARD UNDER THE STEERING STR TOWARD THE SOUTH INDIAN OCEAN. AFTER TAU 72, A TRANSITORY SHORTWAVE TROUGH APPROACHING FROM THE SOUTHWEST WILL ERODE THE STR AND ALLOW THE CYCLONE TO RECURVE SOUTHEASTWARD, MAKE LANDFALL JUST EAST OF PORT HEADLAND SHORTLY AFTER TAU 96, AND TRACK INLAND OVER WESTERN AUSTRALIA. THE FAVORABLE ENVIRONMENT WILL INITIALLY PROMOTE GRADUAL INTENSIFICATION TO 80KTS BY TAU 48. AFTERWARD, LOW VWS AND VERY WARM SST IN THE INDIAN OCEAN WILL FUEL A RAPID INTENSIFICATION (RI) TO A PEAK OF 130KTS BY TAU 96, RIGHT BEFORE LANDFALL. AFTER LANDFALL, INTERACTION WITH THE TERRAIN WILL REDUCE THE INTENSITY TO 45KTS BY TAU 120 AS IT STARTS DISSIPATING OVER LAND.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT WITH THE LAID-OUT FORECAST TRACK, GRADUALLY SPREADING OUT TO A MAXIMUM OF 260NM BETWEEN TAU 72 AND TAU 96, WITH NAVGEM THE NOTABLE LEFT-OF-TRACK OUTLIER. THERE IS HIGH CONFIDENCE IN THE JTWC TRACK FORECAST UP TO TAU 72, THEN LOW AFTERWARD DUE TO THE LAND PASSAGE. THERE IS MEDIUM CONFIDENCE IN THE INTENSITY FORECAST UP TO TAU 72 THEN LOW CONFIDENCE AFTERWARD ON ACCOUNT OF THE HIGH VARIABILITY IN THE INTENSITY GUIDANCE ASSOCIATED WITH RI.

THE AREA OF CONVECTION (INVEST 90W) PREVIOUSLY LOCATED NEAR 8.2N 138.8E IS NOW LOCATED NEAR 9.2N 136.4E, APPROXIMATELY 101 NM WEST OF YAP. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A BROAD LOW-LEVEL CIRCULATION (LLC) WITH FLARING CONVECTION AROUND THE LLC AND FRAGMENTED FORMATIVE BANDING ALONG THE OUTER PERIPHERY. A 090050Z ASCAT-C PASS REVEALS AN ELONGATED LLC WITH A SWATH OF 20 KNOT WINDS OFFSET TO THE NORTH. A RECENT YAP SOUNDING SHOWS A DRY AND STABLE ENVIRONMENT WHILE THE SURFACE OBSERVATIONS INDICATE LIGHT AND VARIABLE WINDS WITH A FLAT PRESSURE TENDENCY OVER THE LAST 24 HOURS. ENVIRONMENTAL ANALYSIS REVEALS MARGINALLY FAVORABLE CONDITIONS FOR DEVELOPMENT WITH MODERATE POLEWARD OUTFLOW ALOFT AND WARM (30-31C) SST, OFFSET BY MODERATE TO HIGH (20-25KT) VWS. GLOBAL MODELS ARE IN AGREEMENT THAT 90W WILL GRADUALLY DEVELOP AS IT TRACKS WEST-NORTHWESTWARD TOWARD THE PHILIPPINES. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 15 TO 20 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1004 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO MEDIUM.

GLOBAL MODELS ARE IN AGREEMENT THAT 90W WILL GRADUALLY DEVELOP AS IT TRACKS WEST-NORTHWESTWARD TOWARD THE PHILIPPINES.