Tropical Cyclone Formation Alert issued for Invest 99P, Invest 90P up-graded to MEDIUM, 08/18utc

JTWC IS ISSUING 3HOURLY SATELLITE BULLETINS ON INVEST 99P AND INVEST 90P.

08/14UTC.

THE AREA OF CONVECTION (INVEST 99P) PREVIOUSLY LOCATED NEAR 18.4S 173.0E IS NOW LOCATED NEAR 18.6S 173.3E, APPROXIMATELY 515 KM WEST-SOUTHWEST OF NADI, FIJI. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) AND A 080716Z AMSR2 91GHZ MICROWAVE IMAGE SHOW CONCENTRATED CONVECTION DISPLACED TO THE NORTHWEST OF A WELL- DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) WITH WEAK CONVECTIVE BANDS ORIENTED IN A NORTH-SOUTH ARC ON THE EASTERN PERIPHERY. A 08948Z ASCAT BULLSEYE FURTHER REVEALS A LARGE SWATH OF 30-35 KNOT WINDS MIRRORING THE CONVECTIVE BANDS ON THE EASTERN EDGE OF THE LLCC WITH 20 KTS WRAPPING INTO THE LLCC IN THE REMAINING QUADRANTS. ENVIRONMENTAL ANALYSIS INDICATES FAVORABLE CONDITIONS FOR TROPICAL CYCLONE DEVELOPMENT WITH MODERATE RADIAL OUTFLOW ALOFT, MODERATE (15- 20KTS) VERTICAL WIND SHEAR (VWS), AND WARM (29C) SEA SURFACE TEMPERATURES (SST). GLOBAL MODELS AGREE THAT 99P WILL CONTINUE TO STRENGTHEN AS IT TRACKS GENERALLY SOUTH-SOUTHEAST. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 25 TO 30 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO HIGH.

GLOBAL MODELS AGREE THAT 99P WILL CONTINUE TO STRENGTHEN AS IT TRACKS GENERALLY SOUTH-SOUTHEAST.

THE AREA OF CONVECTION (INVEST 90P) PREVIOUSLY LOCATED NEAR 12.4S 147.5E IS NOW LOCATED NEAR 13.3S 147.8E, APPROXIMATELY 250 KM NORTH-NORTHEAST OF BOUGAINVILLE REEF, AUSTRALIA. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A CONSOLIDATING LOW- LEVEL CIRCULATION (LLC) WITH PERSISTENT DEEP CONVECTION OBSCURING THE LLC. A 080900Z SSMIS 91GHZ COMPOSITE MICROWAVE IMAGE, HOWEVER, REVEALS SHALLOW BANDING WRAPPING TIGHTLY INTO A DEFINED CENTER WITH DEEP CONVECTION DISPLACED TO THE NORTHWEST. A 081131Z ASCAT-B BULLSEYE IMAGE SHOWS A SWATH OF 25 TO 30 KNOTS OVER THE NORTHERN QUADRANT WITH 15 TO 20 KNOT WINDS ELSEWHERE. ENVIRONMENTAL ANALYSIS INDICATES MARGINALLY FAVORABLE CONDITIONS WITH FAIR OUTFLOW, MODERATE (20KTS) VERTICAL WIND SHEAR (VWS), AND WARM (29-30C) SEA SURFACE TEMPERATURES (SST). GLOBAL MODELS INDICATE 90P WILL GRADUALLY DEEPEN AS IT TRACKS WESTWARD TOWARD THE CAPE YORK PENINSULA. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 20 TO 25 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.