Invest 90W TCFA re-issued// TC 18S rapid intensification forecast next 48h up CAT 4 US//Invest 91W//1106utc

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 13.7N 127.4E IS NOW LOCATED NEAR 12.9N 127.1E, APPROXIMATELY 197 NM EAST OF LEGAZPI, PHILIPPINES. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS AN AREA OF CONVECTION WITH SIGNS OF WRAPPING IN THE MID-TO-UPPER LEVELS OVER THE NORTHWESTERN EDGE OF AN ASSESSED ELONGATED SURFACE TROUGH. UPON CLOSELY MONITORING THIS DISTURBANCE, THERE IS NOT ENOUGH EVIDENCE SUPPORTING AN UPGRADE TO A TROPICAL CYCLONE AT THIS TIME. A 110056Z ASCAT-B PASS SHOWS WINDS OF 20-25 KTS, WITH A SMALL POCKET OF 30-35 KTS IN A CONCENTRATED AREA TO THE WEST OF THE ASSESSED LOW LEVEL CIRCULATION (LLC). HOWEVER, THESE ELEVATED WINDS APPEAR TO BE ASSOCIATED WITH THUNDERSTORM ACTIVITY AND ARE NOT WRAPPING AROUND THE LLC. A 102152Z SSMIS IMAGE ALONG WITH THE MSI LOOP INDICATE THERE IS MID-TO-UPPER LEVEL WRAPPING OF CONVECTIVE BANDING TAKING PLACE, HOWEVER, THERE IS NO SUGGESTION OF A TIGHTENED SURFACE CIRCULATION DUE TO LACK OF ANY SOUTHERLY FLOW. COMPARISON BETWEEN THE 37 GHZ AND 91 GHZ OF THE SSMIS IMAGES REVEALS THE SYSTEM IS TILTED WITH THE UPPER LEVEL CIRCULATION FURTHER TO THE WEST OF THE LOWER LEVEL CIRCULATION. INVEST 90W IS IN A FAVORABLE ENVIRONMENT FOR TROPICAL DEVELOPMENT CHARACTERIZED BY GOOD POLEWARD AND EQUATORWARD OUTFLOW ALOFT, LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS), AND WARM (28-29 C) SEA SURFACE TEMPERATURES (SST). GLOBAL AND DETERMINISTIC MODELS AGREE THAT INVEST 90W WILL TRACK WEST-NORTHWESTWARD AND EVENTUALLY DISSIPATE DUE TO AN INCREASE IN VWS, LAND INTERACTION AND COPIOUS AMOUNTS OF DRY AIR ENTRAINMENT BEING INTRODUCED FROM THE NORTHEAST OVER THE COURSE OF THE NEXT 24-48 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 18 TO 23 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1006 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS HIGH.

GLOBAL AND DETERMINISTIC MODELS AGREE THAT INVEST 90W WILL TRACK WEST-NORTHWESTWARD AND EVENTUALLY DISSIPATE DUE TO AN INCREASE IN VWS, LAND INTERACTION AND COPIOUS AMOUNTS OF DRY AIR ENTRAINMENT BEING INTRODUCED FROM THE NORTHEAST OVER THE COURSE OF THE NEXT 24-48 HOURS.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS DISORGANIZED BLOOMS OF CONVECTION TO THE SOUTHWEST OF AN ASSESSED LOW LEVEL CIRCULATION CENTER (LLCC). A 102159Z SSMIS 91 GHZ PASS SHOWS THE AFOREMENTIONED CONVECTION TO THE SOUTHWEST OF SOME LOW LEVEL BANDING FEATURES WRAPPING INTO THE LLCC. TC EIGHTEEN IS IN A FAVORABLE ENVIRONMENT FOR FURTHER TROPICAL DEVELOPMENT. THESE CONDITIONS ARE CHARACTERIZED BY GOOD POLEWARD OUTFLOW ALOFT, A STRONG 850 MB VORTICITY SIGNATURE, LOW (5-10 KTS) VERTICAL WIND SHEAR (VWS), AND VERY WARM (29-30 C) SEA SURFACE TEMPERATURES (SST). THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON MULTI-AGENCY FIXES, AS WELL AS THE AFOREMENTIONED MSI. THE INITIAL INTENSITY OF 50 KNOTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED OFF A BLEND OF AUTOMATED AND MULTI-AGENCY DVORAKS ESTIMATES.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TC 18S IS RIDING THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE TO THE EAST. AS IT CONTINUES THIS TRAJECTORY, THE SYSTEM WILL INTENSIFY AS THE VWS IS EXPECTED TO LOWER THROUGHOUT THE FORECAST PERIOD. BY TAU 12, THE INTENSITY WILL INCREASE TO 60 KTS, AND THEN FURTHER INCREASING TO 80 KTS BY TAU 24. BY TAU 36, TC 18S WILL BEGIN TO ROUND THE RIDGE AXIS AND SHIFT TO A MORE SOUTHWARD TRACK WHILE IT JUMPS UP TO 105 KTS. UPON COMPLETION OF ROUNDING THE RIDGE AXIS, THE SYSTEM WILL BEGIN A SOUTHEASTWARD TRAJECTORY AND REACH ITS MAX INTENSITY OF 130 KTS. AS TC 18S MAKES ITS APPROACH TO LAND, IT WILL PASS OVER A POOL OF WARMER (30-31 C) SSTS, CONTRIBUTING TO MAINTAINING ITS INTENSITY AS IT PICKS UP TRACK SPEED. JUST AFTER TAU 60, TC 18S WILL MAKE LANDFALL ALMOST AT THE CENTER POINT OF EIGHTY MILE BEACH, AUSTRALIA. AFTER A PERIOD OF LAND INTERACTION, THE SYSTEM WILL BEGIN ITS DISSIPATION PHASE AND DECREASE TO 75 KTS BY TAU 72, FURTHER DECREASING AND BECOME FULLY DISSIPATED BY TAU 96.

MODEL DISCUSSION: THE DETERMINISTIC AND ENSEMBLE MODELS ALL AGREE THAT TC EIGHTEEN WILL CONTINUE TO INTENSIFY AS IT TRANSITS TO THE SOUTHWEST BEFORE ROUNDING THE RIDGE AXIS AND SHIFTING SOUTHWARD AFTER TAU 36, AND FURTHER SHIFTING SOUTHEASTWARD AND CONTINUE TO INTENSIFY AFTER TAU 48. FOR THE JTWC FORECAST TRACK CONSENSUS MEMBERS, THERE IS A 26 NM SPREAD AT TAU 12. THIS TRACK SPREAD GRADUALLY INCREASES TO 102 NM BY TAU 60, JUST BEFORE LANDFALL. GFS AND ECMWF ARE ON THE EASTERN PORTION OF THE CONSENSUS ENVELOPE, WHEREAS NAVGEM AND UK TRACK MODELS ARE ON THE WESTERN PORTION. BECAUSE OF THE GRADUAL INCREASE IN THE TRACK MODEL SPREAD, THE JTWC FORECAST TRACK IS PLACED WITH MEDIUM CONFIDENCE UP TO TAU 72, THEN LOW CONFIDENCE AFTERWARDS. THE INTENSITY CONSENSUS MEMBERS ARE ALSO IN AGREEMENT DISPLAYING A RAPIDLY INTENSIFYING SYSTEM BETWEEN TAUS 24 AND 66, THEN A SUDDEN DROP OFF AFTER TAU 66 WHEN THE SYSTEM MAKES LANDFALL. THE JTWC FORECAST INTENSITY IS SET WITH MEDIUM CONFIDENCE.