WTIO30 FMEE 311820 RSMC / TROPICAL CYCLONE CENTER / LA REUNION TROPICAL CYCLONE FORECAST WARNING (SOUTH-WEST INDIAN OCEAN) 0.A WARNING NUMBER: 19/5/20172018 1.A TROPICAL CYCLONE 5 (CEBILE) 2.A POSITION 2018/01/31 AT 1800 UTC: WITHIN 15 NM RADIUS OF POINT 15.5 S / 76.8 E (FIFTEEN DECIMAL FIVE DEGREES SOUTH AND SEVENTY SIX DECIMAL EIGHT DEGREES EAST) MOVEMENT : WEST 5 KT 3.A DVORAK ANALYSIS: 4.5/5.0/D 0.5/6 H 4.A CENTRAL PRESSURE: 962 HPA 5.A MAX AVERAGE WIND SPEED (10 MN): 80 KT RADIUS OF MAXIMUM WINDS (RMW) :46 KM 6.A EXTENSION OF WIND BY QUADRANTS (KM): 28 KT NE: 240 SE: 330 SW: 410 NW: 200 34 KT NE: 150 SE: 240 SW: 240 NW: 150 48 KT NE: 110 SE: 150 SW: 150 NW: 110 64 KT NE: 90 SE: 100 SW: 100 NW: 90 7.A FIRST CLOSED ISOBAR (PRESSURE / AVERAGE DIAM): 1008 HPA / 1200 KM 8.A VERTICAL EXTENSION OF CYCLONE CIRCULATION : DEEP 1.B FORECASTS: 12H: 2018/02/01 06 UTC: 15.6 S / 75.9 E, MAX WIND=085 KT, TROPICAL CYCLONE 24H: 2018/02/01 18 UTC: 16.2 S / 75.4 E, MAX WIND=085 KT, TROPICAL CYCLONE 36H: 2018/02/02 06 UTC: 16.8 S / 75.3 E, MAX WIND=080 KT, TROPICAL CYCLONE 48H: 2018/02/02 18 UTC: 17.7 S / 75.8 E, MAX WIND=075 KT, TROPICAL CYCLONE 60H: 2018/02/03 06 UTC: 18.3 S / 76.5 E, MAX WIND=065 KT, TROPICAL CYCLONE 72H: 2018/02/03 18 UTC: 19.2 S / 78.0 E, MAX WIND=055 KT, SEVERE TROPICAL STORM 2.B LONGER-RANGE OUTLOOK : 96H: 2018/02/04 18 UTC: 22.0 S / 80.0 E, MAX WIND=050 KT, SEVERE TROPICAL STORM 120H: 2018/02/05 18 UTC: 25.4 S / 80.9 E, MAX WIND=050 KT, POST-TROPICAL DEPRESSION 2.C ADDITIONAL INFORMATION: T=4.5+;CI=5.0 OVER THE LAST 6 HOURS, THE WESTERN SEMI-CIRCLE OF CEBILE'S EYE HAS DETERIORATED ON THE IR IMAGES. AS THE UPPER DIVERGENCE REMAINS IMPRESSIVE, THE MOST PROBABLE CAUSE OF THIS TEMPORARY DEGRADATION REMAINS THE INFLUENCE OF THE MID-TROPOSPHERIC DRY AIR STILL LOCATED CLOSE TO THE WEST OF THE CYCLONE. HOWEVER, ON THE VERY LAST SAT IMAGES, CONVECTION STRENGTHENED AGAIN. THE RSMC DVORAK ESTIMATES IS STILL LIMITED BY THE LARGE EYE SIZE. CEBILE KEEPS ON TRACKING MAINLY WESTWARDS, WITH A SLIGHT WEST-NORTH-WESTWARD TENDENCY. THE SYSTEM IS CAUGHT BETWEEN A SUBTROPICAL RIDGE IN THE SOUTH-WEST AND THE NEAR-EQUATORIAL RIDGE IN THE NORTH-EAST. THESE TWO SYNOPTIC STRUCTURES ARE DRIVING OPPOSITE STEERING FLOWS BUT THE SUBTROPICAL INFLUENCE IS CURRENTLY CLEARLY THE STRONGEST. HOWEVER, FROM TOMORROW, THE SUBTROPICAL RIDGE IS EXPECTED TO WEAKEN AND SLIDE WESTWARD. THE NEAR EQUATORIAL RIDGE SHOULD THUS TAKE OVER CEBILE'S STEERING FLOW. THIS CHANGE WILL LEAD TO A SHARP SOUTH-EASTWARD TURN FOLLOWED BY A GRADUAL ACCELERATION. THE GUIDANCE DISPERSION REMAINS IMPORTANT BECAUSE OF THE UNCERTAINTY OVER THE EXACT DIRECTION OF THE TRACK OF CEBILE OVER THE NIGHT. AFTER THE TURN, THE MAIN UNCERTAINTY CONCERNS THE CYCLONE'S SPEED. THE CURRENT TRACK FORECAST IS MOSTLY BASED ON A CONSENSUS OF RECENT IFS AND GFS GUIDANCE. CEBILE IS CURRENTLY WITHIN QUASI-PERFECT CONDITIONS CONCERNING WIND SHEAR, UPPER DIVERGENCE AND OCEANIC HEAT CONTENT. A SLIGHT INTENSITY GAIN IS STILL POSSIBLE AT SHORT RANGE. FROM FRIDAY, EQUATORWARD UPPER LEVEL DIVERGENCE IS EXPECTED TO WEAKEN AND A WESTERLY WINDSHEAR CONSTRAINT BEGINS TO APPEAR. FROM SATURDAY, A ROSSBY WAVE BREAKING LOCATED WEST OF THE SYSTEM WILL QUICKLY STRENGTHEN THE WESTERLY THEN NORTHWESTWERLY WINDSHEAR. CEBILE'S INTENSITY IS FORECAST TO QUICKLY DROP, AS IT WILL ALSO TRACK OVER COOLER SURFACE SEA TEMPERATURES. LASTLY, THE SYSTEM MAY THEN BEGIN ITS EXTRA-TROPICALISATION PHASE AS THE UPPER TROUGH MATERIALIZING THE ROSSBY WAVE IS COMING CLOSER TO THE SYSTEM'S CORE.=