90W gradually developing approaching the Philippines //TC 18S forecast to be a powerful CAT 4 US by 72h and landfall East of Pardoo//1003utc

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

THE AREA OF CONVECTION (INVEST 90W) PREVIOUSLY LOCATED NEAR 9.2N 136.4E IS NOW LOCATED NEAR 10.6N 134.6E, APPROXIMATELY 656 NM EAST- SOUTHEAST OF LEGAZPI, PHILIPPINES. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A BROAD LOW-LEVEL CIRCULATION (LLC) WITH THE STRONGEST CONVECTION TO THE NORTH OF THE LLC. A RECENT SURFACE OBSERVATIONS 041000Z SHOWS WINDS COMING FROM THE EAST AT 20 KNOTS AND WITH A MEAN SEA LEVEL PRESSURE 1004 MB. ENVIRONMENTAL ANALYSIS REVEALS FAVORABLE CONDITIONS FOR DEVELOPMENT WITH MODERATE POLEWARD OUTFLOW ALOFT, LOW TO MODERATE VERTICAL WIND SHEAR (15-20KTS), AND WARM (30-31C) SST. 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 20 TO 24 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 HIGH.

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

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A MEDIUM-SIZED SYSTEM WITH FLARING CENTRAL CONVECTION AND FRAGMENTED SPIRAL BANDING FEEDING IN FROM ALL QUADRANTS INTO THE COLD DENSE OVERCAST THAT IS OBSCURING THE LOW LEVEL CIRCULATION. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON EXTRAPOLATION FROM NOTCH FEATURE IN THE 092213Z SSMIS 37GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY IS BASED WITH MEDIUM CONFIDENCE FROM AN OVERALL ASSESSMENT OF AGENCY AND AUTOMATED DVORAK ESTIMATES AND CONSISTENT WITH THE IMPROVED CONVECTIVE SIGNATURE OVER THE PAST SIX HOURS. TC 18S IS IN A FAVORABLE ENVIRONMENT WITH LIGHT 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 IN THE SOUTH INDIAN OCEAN. AFTER TAU 48, 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 JUST AFTER TAU 72, AND TRACK INLAND OVER WESTERN AUSTRALIA. THE FAVORABLE ENVIRONMENT WILL INITIALLY PROMOTE GRADUAL INTENSIFICATION TO 85KTS BY TAU 36. AFTERWARD, LOW VWS, INCREASED OUTFLOW AHEAD OF THE SHORTWAVE TROUGH, AND VERY WARM SST IN THE INDIAN OCEAN WILL FUEL A RAPID INTENSIFICATION (RI) TO A PEAK OF 130KTS BETWEEN TAU 48 AND TAU 72. AFTER LANDFALL, INTERACTION WITH THE TERRAIN WILL REDUCE THE INTENSITY TO 55KTS BY TAU 96 THEN TO DISSIPATION BY TAU 120.

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL TIGHT AGREEMENT WITH THE LAID-OUT FORECAST TRACK, GRADUALLY SPREADING OUT TO A JUST 165NM BY TAU 120. IN VIEW OF THIS, 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.