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Rare Tropical Cyclone Forms Off Brazil March 12, 2010
A rare South Atlantic subtropical cyclone can be seen swirling clockwise off the coast of southern Brazil.
A compact swirl of clouds off the southern coast of Brazil on Tuesday became what was only the 7th subtropical or tropical cyclone to form in the South Atlantic basin in recorded history.

Dubbed “Invest 90Q” by tropical weather monitors, the subtropical feature was producing almost tropical storm wind speeds of 40 mph by early Wednesday morning.

Since such weather features are so rare in the Atlantic south of the Equator, there is no official naming protocol by regional weather offices.

Weather Underground director of meteorology Jeff Masters points out in his blog that Brazil has experienced only one landfalling tropical cyclone in recorded history.

Eventually dubbed Cyclone Catarina, that storm swirled off the coast of southern Brazil for nearly a week in March 2004 before roaring ashore.

Catarina killed three people, destroyed 1,500 homes and damaged around 40,000 others. Extensive damage was also reported to banana and rice crops.

Invest 90Q formed very near where Catarina was spawned by a rare combination of favorable conditions.

Tropical cyclones are infrequent in the South Atlantic due to strong upper-air wind sheer, cool ocean temperatures and the lack of disturbances to initiate a spin.

Masters writes that there are no African waves in the South Atlantic, and the Intertropical Convergence Zone, key to cyclone development elsewhere, doesn’t exist in the proper location to spawn tropical storms.

Satellite Loop Data: CIMSS