TC 21S(OLGA) SAR reveals still a bit stronger than expected// INVEST 97P// ECMWF 10 Day Storm Traccks// 0903utc

JTWC IS ISSUING 6HOURLY WARNINGS AND 3HOURLY SATELLITE BULLETINS ON TC 21S(OLGA)

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A TIGHTLY WRAPPED, BUT SHALLOW EXPOSED LOW-LEVEL CIRCULATION CENTER WITH FLARING DEEP CONVECTION OCCURRING ALONG THE CONVERGENT FLOW IN THE SOUTHERN SEMICIRCLE. SIGNIFICANT NORTHWESTERLY VERTICAL WIND SHEAR (VWS) IS BLOWING OFF ALL CONVECTION TO THE SOUTHEAST, WITH OUTFLOW ENHANCED BY A SUBTROPICAL JET POSITIONED TO THE SOUTH. ENVIRONMENTAL ANALYSIS INDICATES THAT TC 21S IS LOCATED IN AN UNFAVORABLE ENVIRONMENT FOR DEVELOPMENT CHARACTERIZED BY HIGH (35-40 KTS) VWS AND THE PRESENCE OF MID-LEVEL DRY AIR IN THE NORTHERN AND WESTERN SECTORS. THE STRONG OUTFLOW AND WARM (29-30 DEGREE CELSIUS) SEA SURFACE TEMPERATURES PRESENT ARE KEEPING THE SYSTEM FROM MORE RAPID WEAKENING. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC SEEN IN THE ANIMATED MSI. THE INITIAL INTENSITY OF 50 KTS IS ASSESSED WITH MEDIUM CONFIDENCE BASED ON A RANGE OF SUBJECTIVE DVORAK ESTIMATES FROM T3.0-3.5, AND FURTHER SUPPORTED BY 082148Z SAR WIND SPEED PRODUCT SHOWING A BROAD SWATH OF

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING, BUT THE TRACK WAS SHIFTED SLIGHTLY CLOSER TO THE EXMOUTH PENINSULA, AND THE INITIAL INTENSITY WAS INCREASED TO 50 KTS TO REFLECT THE 082148Z SAR DATA PREVIOUSLY MENTIONED. FORECAST DISCUSSION: TC 21S IS FORECAST TO CONTINUE ON A SOUTHWESTWARD TRACK OVER THE FORECAST PERIOD, ALONG THE WESTERN PERIPHERY OF A REFLECTION OF A STR POSITIONED TO THE SOUTH. THE JTWC TRACK HAS BEEN SHIFTED SLIGHTLY TO THE EAST AS MODEL GUIDANCE HAS SUGGESTED A MORE SOUTHERLY TRACK THAN PRIOR GUIDANCE. THE CPA TO LEARMONTH IS 73 NM AT 102300Z, WHICH IS A 30 NM DECREASE FROM THE PREVIOUS FORECAST. VWS VALUES ARE ANTICIPATED TO REACH OVER 50 KTS BY TAU 24, AIDING IN THE WEAKENING OF THE SYSTEM. ADDITIONALLY, DRY AIR IS EXPECTED TO PERSIST FOR THE REMAINDER OF THE LIFE OF TC 21S. AS A RESULT, THE INTENSITY FORECAST CALLS FOR A CONTINUED WEAKENING TREND, WITH DISSIPATION OCCURRING BY TAU 48.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT WITH A 140 NM CROSS-TRACK SPREAD IN GUIDANCE AT TAU 72. GFS HAS SHIFTED TO BECOME THE EASTERNMOST MEMBER OF CONSENSUS, GRAZING THE EXMOUTH PENINSULA. THE CONSENSUS MEAN IS APPROXIMATELY 75 NM TO THE WEST. INTENSITY GUIDANCE CONTINUES TO AGREE WITH A WEAKENING TREND THROUGH THE FORECAST PERIOD. HAFS-A SUGGESTS A SLIGHTLY MORE GRADUAL DECREASE, WITH DISSIPATION AFTER TAU 72. OVERALL, THE JTWC INTENSITY FORECAST IS ASSESSED WITH MEDIUM CONFIDENCE.

082148Z SAR WIND SPEED PRODUCT SHOWING A BROAD SWATH OF 50 TO 55 KT WINDS IN THE SOUTHWESTERN QUADRANT.