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Subject: G6) Why doesn't the South Atlantic Ocean experience tropical
cyclones?
Contributed by Chris Landsea
What never ?? Well, hardly ever.
In March, 2004 a hurricane DID form in the South Atlantic
Ocean and made landfall in Brazil. But this still leaves
the question of why hurricanes are so rare in the South
Atlantic. Though many people might speculate that the sea surface
temperatures are too cold, the primary reasons that the South
Atlantic Ocean gets few tropical cyclones are that the tropospheric
(near surface to 200mb) vertical wind shear is much too strong
and there is typically no inter-tropical convergence zone (ITCZ)
over the ocean (Gray 1968).
Without an ITCZ to provide synoptic vorticity and convergence
(i.e. large scale spin and thunderstorm activity) as well as
having strong wind shear, it becomes very difficult to nearly
impossible to have genesis of tropical cyclones. Penn State University
offers a write up on the South Atlantic hurricane
here.
In addition, McAdie and Rappaport
(1991) documented the occurrence of a strong tropical
depression/weak tropical storm that formed off the coast of Congo
in mid-April of 1991. This storm lasted about five days and drifted
toward the west-southwest into the central South Atlantic. So far,
there has not been a systematic study as to the conditions that
accompanied this rare event.
Last updated July 13, 2005
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