300300Z POSITION NEAR 14.2S 44.0E.
TROPICAL CYCLONE (TC) 21S (HELLEN), LOCATED APPROXIMATELY 345 NM
NORTH-NORTHWEST OF ANTANANARIVO, MADAGASCAR, HAS TRACKED
SOUTHEASTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED
INFRARED (EIR) SATELLITE IMAGERY DEPICTS A WELL-DEVELOPED SYSTEM
THAT CONTINUES TO RAPIDLY INTENSIFY AND HAS FORMED A RAGGED EYE WITH
DEEP CONVECTIVE BANDING SURROUNDING THE EYE. THE INITIAL POSITION IS
BASED ON THE RAGGED EYE FEATURE WITH GOOD CONFIDENCE. THE CURRENT
INTENSITY OF 90 KNOTS IS BASED ON CONGRUENT DVORAK INTENSITY
ESTIMATES FROM ALL REPORTING AGENCIES. UPPER-LEVEL ANALYSIS
INDICATES THE SYSTEM IS LOCATED IN A FAVORABLE ENVIRONMENT OF
EXCELLENT OUTFLOW AND LOW TO MODERATE (05 TO 15 KNOT) VERTICAL WIND
SHEAR. ADDITIONALLY, WARM SEA SURFACE TEMPERATURES IN THE MOZAMBIQUE
CHANNEL ARE CONDUCIVE FOR FURTHER RAPID INTENSIFICATION. THE
FAVORABLE UPPER-LEVEL ENVIRONMENT IS EXPECTED TO REMAIN THROUGH TAU
24, ALLOWING TC 21S TO RAPIDLY INTENSIFY AND LEADING TO A PEAK
INTENSITY OF 120 KNOTS BY TAU 24. TC HELLEN IS FORECAST TO CONTINUE
SLOWLY DRIFTING SOUTHEASTWARD IN A WEAK STEERING ENVIRONMENT. THIS
WEAK STEERING ENVIRONMENT IS FORECAST TO PERSIST FOR THE NEXT 36
HOURS UNTIL A SUBTROPICAL RIDGE (STR) WILL BUILD IN FROM THE SOUTH
BY TAU 48, DOMINATING THE STEERING ENVIRONMENT AND DRIVING TC 21S ON
A WEST-SOUTHWESTWARD TRACK. DYNAMIC MODEL GUIDANCE IS IN FAIR
AGREEMENT WITH A TRACK TO THE SOUTHEAST THROUGH TAU 36, BUT GREATLY
DIVERGES AFTERWARDS DUE TO A COMPETING ENVIRONMENT BETWEEN THE NEAR
EQUATORIAL RIDGE TO THE NORTHEAST AND STR TO THE SOUTH. DUE TO THE
UNCERTAINTY ASSOCIATED WITH THE WEAK STEERING ENVIRONMENT WHICH IS
CAUSING SLOW TRACK SPEEDS AND POSSIBLY QUASISTATIONARY AND ERRATIC
MOVEMENT IN THE NEAR TERM, THE JTWC FORECAST TRACK IS POSITIONED
CLOSE TO THE MULTI-MODEL CONSENSUS WITH LOW CONFIDENCE. MAXIMUM
SIGNIFICANT WAVE HEIGHT AT 300000Z IS 23 FEET. DUE TO RAPID
INTENSIFICATION OVER THE PAST 6 HOURS, THE WARNING CYCLE HAS BEEN
SHIFTED TO REFLECT THE CURRENT INTENSITY OF 90 KNOTS AS WELL AS THE
SIGNIFICANT CHANGE TO THE PEAK INTENSITY OF 120 KNOTS AT TAU 24.
- JTWC
