202100Z POSITION NEAR 27.9S 38.4E.
TROPICAL CYCLONE (TC) 15S (GUITO), LOCATED APPROXIMATELY 695 NM
SOUTHWEST OF ANTANANARIVO, MADAGASCAR, HAS TRACKED SOUTHWARD AT
16 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR)
SATELLITE IMAGERY DEPICTS WEAKENING DEEP CONVECTION, WITH PERSISTENT
SPIRAL BANDING WRAPPED INTO THE LOW-LEVEL CIRCULATION CENTER (LLCC).
A 201808Z MICROWAVE IMAGE ALSO REVEALS THE BULK OF THE DEEP
CONVECTIVE BANDING OVER THE SOUTHERN SEMI-CIRCLE TIGHTLY WRAPPED
INTO A WELL-DEFINED LLCC. THE CURRENT POSITION IS BASED ON
AFOREMENTIONED MICROWAVE IMAGE WITH HIGH CONFIDENCE. THE INITIAL
INTENSITY OF 65 KNOTS IS BASED ON THE WELL ORGANIZATION AND DVORAK
CURRENT INTENSITY ESTIMATES FROM PGTW, KNES AND FMEE. UPPER-LEVEL
ANALYSIS INDICATES THE SYSTEM IS LOCATED IN AN AREA OF LOW TO
MODERATE VERTICAL WIND SHEAR (VWS) AND STRONG POLEWARD OUTFLOW WHICH
IS EVIDENT IN THE ANIMATED WATER VAPOR IMAGERY. HOWEVER, UPPER-
LEVEL CONVERGENCE ASSOCIATED WITH THE INTERACTION BETWEEN AN
APPROACHING MID-LATITUDE TROUGH FROM THE WEST AND SUBTROPICAL RIDGE
ANCHORED TO THE EAST IS CAUSING SUBSIDENCE OVER THE WESTERN SEMI-
CIRCLE, HINDERING THE DEVELOPMENT. BY TAU 24, THE DECREASING SEA
SURFACE TEMPERATURES AND INCREASING VWS WILL CONTINUE TO WEAKEN TC
15S. BY TAU 36, INTERACTION WITH THE MID-LATITUDE WESTERLIES WILL
START THE EXTRA-TROPICAL TRANSITION (ETT) PROCESS AND IS EXPECTED TO
COMPLETE ETT BY TAU 60. MODEL GUIDANCE IS IN EXCELLENT AGREEMENT
LENDING HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. MAXIMUM
SIGNIFICANT WAVE HEIGHT AT 201800Z IS 25 FEET.
- JTWC
