181500Z POSITION NEAR 18.7S 40.2E.
TROPICAL CYCLONE (TC) 15S (FIFTEEN), LOCATED APPROXIMATELY 375 NM
WEST OF ANTANANARIVO, MADAGASCAR, HAS TRACKED SOUTHWARD AT 05 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
SHOWS THE SYSTEM HAS FURTHER CONSOLIDATED AS FORMATIVE BANDS HAVE
WRAPPED TIGHTER INTO THE LOW LEVEL CIRCULATION CENTER (LLCC) EVEN IF
THE CONVECTIVE CELLS ARE STILL FRAGMENTED. THE INITIAL POSITION IS
BASED ON THE ABOVE ANIMATION WITH FAIR CONFIDENCE. THE INITIAL
INTENSITY OF 35 KNOTS IS BASED ON AN 180903Z SCATTEROMETRY PASS
SHOWING 35 TO 40 KNOT WIND BARBS ALONG THE WESTERN ARC OF A SYMMETRIC
LLCC. THIS IS HIGHER THAN AGENCY DVORAK ESTIMATES THAT ARE
CONSTRAINED BY THE FRAGMENTED CONVECTION. UPPER LEVEL ANALYSIS
INDICATES THE SYSTEM IS UNDER A RIDGE AXIS IN AN AREA OF LOW (05-10
KNOT) VERTICAL WIND SHEAR (VWS). ADDITIONALLY, ANIMATED WATER VAPOR
ANIMATION SHOWS A GOOD RADIAL OUTFLOW WITH A POLEWARD BIAS THAT IS
ENHANCING THE ASSOCIATED CONVECTION. THE SYSTEM IS TRACKING ALONG THE
WESTERN PERIPHERY OF A LOW- TO MID-LAYERED SUBTROPICAL RIDGE TO THE
EAST. AFTER TAU 48, A MID-LATITUDE TROUGH APPROACHING FROM THE
SOUTHWEST IS EXPECTED TO WEAKEN THE RIDGE AND CAUSE TC 15S TO RECURVE
SOUTHEASTWARD. THE SYSTEM WILL SLOWLY INTENSIFY MAINLY DUE TO THE
STRONG OUTFLOW. HOWEVER, INTENSIFICATION WILL BE MINIMAL DUE TO
INCREASING VWS AND COOLING SEA SURFACE TEMPERATURES AS THE CYCLONE
DRIFTS POLEWARD. THE AVAILABLE NUMERIC GUIDANCE IS IN UNUSUALLY CLOSE
AGREEMENT FOR A CYCLONE IN A DEVELOPING STAGE, LENDING HIGH
CONFIDENCE TO THE JTWC TRACK FORECAST. GFDN IS THE LONE OUTLIER,
UNREALISTICALLY TRACKING THE VORTEX WESTWARD AFTER TAU 48. MAXIMUM
SIGNIFICANT WAVE HEIGHT AT 181200Z IS 10 FEET.
- JTWC
