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Tropical Cyclone Twenty One (21S) Tracking West-southwestward

11.8S 60.4E

April 8th, 2013 Category: Tropical Storms

Tropical Storm Twenty One (21S) – April 7th, 2013

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Track of Tropical Storm Twenty One (21S) - April 8th, 2013 © Univ. of Wisconsin

Track of TC 21S

Tropical Cyclone Twenty One (TC 21S), located approximately 335 nm southwest of Diego Garcia, has tracked west-southwestward at 11 knots over the past six hours. Maximum significant wave height is 15 feet.

Animated infrared satellite imagery depicts a partially-exposed low-level circulation center (LLCC) located east of persistent deep convection. A SSMIS 37 ghz image shows good lower-level banding structure over the western semicircle but very fragmented and weak bands to the east.
An ASCAT pass depicted 35-40 knot winds over the western portion of the LLCC which are wrapping into the center.

The current position is based on the aforementioned imagery with fair confidence. The current intensity is based on the timely ASCAT pass. Upper-level analysis indicates TC 21S is approximately five degrees equatorward of the subtropical ridge (STR) axis. Vertical wind shear (VWS) remains moderate (15-20 knots), causing the deep convection to be sheared to the west. Animated water vapor imagery depicts moderate poleward outflow; however, equatorward outflow is limited due to troughing.

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