| Summary: | Tropical storms occur in nearly every ocean basin in the world; it has long been thought that the South Atlantic was the exception. However, in March 2004 Hurricane Catarina disproved this assumption. Hurricane Catarina developed due to the evolution of a subtropical storm (ST) into a hurricane. In fact, as the climatology compiled in this study will document, many subtropical storms have formed within the South Atlantic basin within the last 51 years (1957-2007). A climatology of subtropical storms off the east coast of Australia is also compiled over the same time period. While both the South Atlantic basin and the Tasman Sea region ST bear striking resemblance to the ST documented in Guishard (2006), many differences exist between the two hemispheres, such as preferred season of development. A subtropical storm is defined simply as a system with gale-force winds displaying a hybrid structure with an upper-level cold core and lower-level warm core (e.g. Guishard 2006). While these criteria are straight-forward, applying them in a construction of a ST climatology for the two Southern Hemisphere basins is more challenging. In compiling a climatology for the South Atlantic basin and the Tasman Sea region, the mechanism for ST formation in the Southern Hemisphere was found to be quite different than that of the North Atlantic basin. Thus, additional criteria were implemented in order to separate the ST from midlatitude systems which could be mistakenly classified as ST due to their similar structure and apparent hybrid state.
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