282100Z POSITION NEAR 13.0S 42.5E.
TROPICAL CYCLONE 21S (TWENTYONE), LOCATED APPROXIMATELY 462 NM
NORTHWEST OF ANTANANARIVO, MADAGASCAR HAS TRACKED EAST-
SOUTHEASTWARD AT 05 KNOTS OVER THE PAST SIX HOURS.
ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) DEPICTS A
STEADILY CONSOLIDATING SYSTEM WITH DEEPENING CENTRAL CONVECTION
AND A FRAGMENTED BANDING FEATURE TO THE WEST OF THE LOW-LEVEL
CIRCULATION CENTER (LLCC). THE LLCC HAS CONTINUED MOVING FURTHER
OFFSHORE ALLOWING FOR THE RECENT DEVELOPMENT. A 281735Z SSMIS
IMAGE ALSO REVEALS MULTIPLE CURVED BANDS WRAPPING INTO THE SYSTEM
CENTER. THE INITIAL POSITION IS BASED ON THE 37 GHZ SSMIS IMAGE
AS WELL AS THE EIR WITH HIGH CONFIDENCE. THE INITIAL INTENSITY IS
ASSESSED AT 35 KNOTS BASED ON CONGRUENT DVORAK INTENSITY ESTIMATES
FROM PGTW, KNES, AND FMEE. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM
REMAINS IN A FAVORABLE ENVIRONMENT WITH LOW TO MODERATE (5-15 KNOT)
VERTICAL WIND SHEAR AND STRONG EASTWARD AND POLEWARD OUTFLOW
CHANNELS. ADDITIONALLY, WARM SEA SURFACE TEMPERATURES IN THE
MOZAMBIQUE CHANNEL ARE CONDUCIVE FOR FURTHER DEVELOPMENT. HOWEVER,
THE CYCLONES PROXIMITY TO THE AFRICAN LANDMASS MAY BE LIMITING THE
INFLUX OF MOISTURE NECESSARY FOR DEEP DEVELOPMENT. OVER THE PAST 48
HOURS A SERIES OF OUTFLOW BOUNDARIES HAVE BEEN OBSERVED IN
MULTISPECTRAL SATELLITE IMAGERY WHICH MAY BE AN INDICATOR OF THE
PRESENCE OF DRIER AIR IN THE MID-LEVELS. FOR THIS REASON THE SYSTEM
MAY STRUGGLE TO INTENSIFY OR MAINTAIN DEEPER DEVELOPMENT. TC 21S IS
FORECAST TO SLOWLY DRIFT TO THE SOUTHEAST IN A WEAK STEERING
ENVIRONMENT TOWARDS THE NORTHWEST COAST OF MADAGASCAR. AFTER THIS
AN ABRUPT TURN TO THE WEST IS ANTICIPATED DUE TO RIDGING BUILDING IN
TO THE EAST AND WEST OF THE CYCLONE. THE SYSTEM IS SUBSEQUENTLY
FORECAST TO WEAKEN DUE TO DEGRADING UPPER-LEVEL CONDITIONS AND
POTENTIAL LAND INTERACTION. DYNAMIC MODEL GUIDANCE IS IN FAIR
AGREEMENT INDICATING A MODERATE SPREAD IN TRACK SOLUTIONS
WITH THE EXCEPTION OF GFS, WHICH HAS CONSISTENTLY INDICATED A
SOUTHEAST TRACK OVER MADAGASCAR. DUE TO THE AMOUNT OF UNCERTAINTY
ASSOCIATED WITH THE WEAK STEERING ENVIRONMENT THE JTWC FORECAST
TRACK IS LAID CLOSE TO THE MULTI-MODEL CONSENSUS WITH LOW
CONFIDENCE. MAXIMUM SIGNIFICANT WAVE HEIGHT AT 281800Z IS 10 FEET.
NEXT WARNINGS AT 290900Z AND 292100Z. THIS WARNING SUPERSEDES AND
CANCELS REF A, JOINT TYPHOON WRNCEN PEARL HARBOR HI 272000Z MAR
14 TROPICAL CYCLONE FORMATION ALERT (WTXS21 PGTW 272000). - JTWC
