WTIO30 FMEE 141254 RSMC / TROPICAL CYCLONE CENTER / LA REUNION TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN) 0.A WARNING NUMBER: 20/5/20142015 1.A TROPICAL CYCLONE 5 (BANSI) 2.A POSITION 2015/01/14 AT 1200 UTC: WITHIN 20 NM RADIUS OF POINT 17.4 S / 59.2 E (SEVENTEEN DECIMAL FOUR DEGREES SOUTH AND FIFTY NINE DECIMAL TWO DEGREES EAST) MOVEMENT : EAST 4 KT 3.A DVORAK ANALYSIS: 4.5/5.0/W 1.0/24 H 4.A CENTRAL PRESSURE: 964 HPA 5.A MAX AVERAGE WIND SPEED (10 MN): 75 KT RADIUS OF MAXIMUM WINDS (RMW) :61 KM 6.A EXTENSION OF WIND BY QUADRANTS (KM): 28 KT NE: 410 SE: 740 SW: 310 NW: 370 34 KT NE: 260 SE: 260 SW: 220 NW: 240 48 KT NE: 130 SE: 130 SW: 130 NW: 130 64 KT NE: 100 SE: 100 SW: 100 NW: 100 7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1004 HPA / 900 KM 8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION : DEEP 1.B FORECASTS: 12H: 2015/01/15 00 UTC: 17.8 S / 60.0 E, MAX WIND=080 KT, TROPICAL CYCLONE 24H: 2015/01/15 12 UTC: 18.5 S / 61.0 E, MAX WIND=090 KT, INTENSE TROPICAL CYCLONE 36H: 2015/01/16 00 UTC: 19.5 S / 62.4 E, MAX WIND=090 KT, INTENSE TROPICAL CYCLONE 48H: 2015/01/16 12 UTC: 21.1 S / 64.3 E, MAX WIND=090 KT, INTENSE TROPICAL CYCLONE 60H: 2015/01/17 00 UTC: 22.8 S / 66.1 E, MAX WIND=085 KT, TROPICAL CYCLONE 72H: 2015/01/17 12 UTC: 24.3 S / 68.2 E, MAX WIND=080 KT, POST-TROPICAL DEPRESSION 2.B LONGER-RANGE OUTLOOK : 96H: 2015/01/18 12 UTC: 26.2 S / 74.3 E, MAX WIND=070 KT, POST-TROPICAL DEPRESSION 120H: 2015/01/19 12 UTC: 27.1 S / 79.5 E, MAX WIND=060 KT, POST-TROPICAL DEPRESSION 2.C ADDITIONAL INFORMATIONS: T=4.5- CI=5.0- METEOSAT7 IMAGERY REVEALS THAT BANSI HAS GREAT TROUBLE TO COMPLETE ITS EYEWALL REPLACEMENT CYCLE. DVORAK SIGNATURE SHOWS CONSEQUENTLY NUMEROUS OSCILLATION, THE MENTIONED FINAL T-NUMBER IS AN AVERAGE OVER THE PAST 6 HOURS. TODAY, THE MID-LEVEL RIDGE SHIFTS BACK TO THE NORTH-EAST OF THE SYSTEM AND A COL BUILDS TO THE SOUTH. BANSI IS THEREFORE TO RESUME ON A SLOW EAST-SOUTH-EASTWARDS MOTION. THURSDAY, THE STRONG WESTERLIES SOUTH OF THE NEAR EQUATORIAL HIGHS SHOULD SPEED UP THE FORWARD MOTION. FRIDAY, A NEW SOUTH-EASTWARDS TURN IS EXPECTED OVER THE SOUTHWESTERN EDGE OF A BUILDING STR BEFORE A FINAL EAST-SOUTH-EASTWARDS TURN NORTH OF A MID LEVEL TROUGH AS THE SYSTEM WILL MOVE OUT OF THE TROPICAL DOMAIN. ON THIS FORECAST TRACK, ENVIRONMENTAL CONDITIONS ARE VERY FAVOURABLE UNTIL THURSDAY NIGHT UNDER THE UPPER LEVEL RIDGE AXIS AS AT LEAST 2 UPPER LEVEL CHANNELS EQUATOR-WARD AND POLEWARD REMAIN IN PLACE WITHIN THE PERIOD. HOWEVER IT IS THE INNER-CORE DYNAMICS THAT WILL GOVERN THE INTENSITY FORECAST POTENTIALLY COUPLED WITH A NEGATIVE FEEDBACK OF THE SST AS THE SYSTEM HAS MOVED LITTLE SINCE YESTERDAY AFTERNOON ... AS THIS MECHANISMS ARE STILL NOT OR POORLY DESCRIBED WITH THE CURRENT NUMERICAL GUIDANCE, THIS INTENSITY FORECAST REMAINS A TOUGH ONE. WHEN THE ERC WILL FINISHED, SOME RE-INTENSIFICATION IS EXPECTED BUT THE IMPORTANT THING IS THE ONGOING CHANGE IN THE STRUCTURE THAT WILL LEAD TO SIGNIFICANT EXTENSION OF THE WIND-FIELD (UP TO FRIDAY THE MEAN RADIUS OF THE GALES WINDS MAY REACH 300 KM AND MAY REACH 400 TO 500 KM NORTH AND SOUTH OF THE SYSTEM) THURSDAY NIGHT, BANSI IS LIKELY TO MOVE SOUTH OF THE UPPER LEVEL RIDGE AXIS AND AN UPPER LEVEL TROUGH SHOULD GETTING CLOSER FROM ITS SOUTHWEST. THEREFORE, VERTICAL WINDSHEAR SHOULD INCREASE BY THAT TIME. ON FRIDAY, BANSI IS LIKELY TO BEGIN TO WEAKEN OWING TO WESTERLY VERTICAL WINDSHEAR AND THE LOWERING OCEANIC HEAT CONTENT. HOWEEVER VERY STRONG WINDS ARE EXPECTED TO MAINTAIN BY THAT TIME EVEN WHEN THE SYSTEM WILL SHOW SOME POST-TROPICAL CHARACTERISTICS. DUE TO THE EXPECTED STRONG WINDS EXTENSION (AFTER THE ERC) AND SOME POTENTIAL FOR RE-INTENSIFICATION, BANSI WILL REMAIN AN EXTREMELY DANGEROUS SYSTEM WITHIN THE NEXT FEW DAYS. CYCLONIC SWELL ASSOCIATED WITH BANSI WILL GROW ALONG THE EXPOSED MASCAREIGNES ISLANDS SHORELINES WITHIN THE NEXT FEW DAYS. NUMERICAL STORM SURGE SIMULATIONS GIVE AS RESULTS : FOR THE SOUTH OF ST-BRANDON ARCHIPELAGO : 0.80 TO 1.30M FOR RODRIGUES ISLAND : 1M50 TO 2M50 NOTE THAT THIS STORM SURGE FORECAST IS TO TAKE WITH CAUTION AND DOES NOT TAKE IN ACCOUNT THE ADDITIONAL SUBMERSION EFFECTS DUE TO THE CYCLONIC SWELL AND THE ASTRONOMIC TIDE. THEREFORE, THE INHABITANTS OF RODRIQUES ISLAND (INCREASING THREAT WITH SEVERE WEATHER CONDITIONS EXPECTED TO SPREAD THURSDAY AND A CLOSEST POINT APPROACH EXPECTED THURSDAY NIGHT) SHOULD CLOSELY MONITOR THE PROGRESS OF THIS DANGEROUS SYSTEM.=