Rare Formation
Typically, tropical cyclones do not form in the South Atlantic Ocean, due to strong upper level shear, cool water temperatures, and the lack of a convergence zone of convection. Occasionally though, as seen in 1991 and early 2004, conditions can become slightly more favorable. For Catarina, it was a combination of climatic and atmospheric anomalies. Water temperatures on Catarina's path ranged from 24 to 25 °C, slightly less than the 26.5 °C temperature of a normal tropical cyclone, but sufficient for a storm of baroclinic origin.
Up to that point, no tropical cyclone had been observed to reach hurricane strength in the South Atlantic Ocean via satellite imagery, which dates back to the mid-1970s. While Catarina formed in an unusual area, its relation to global warming or any other type of global climatic change is still up for debate. The Brazilian Society of Meteorology attributed it to "climatic changes and atmospheric anomalies," while other researchers have indicated that it could be the result of the Southern Annular Mode or other seasonal variations in weather within the Southern Hemisphere, again linked to global changes in climate. However, more research in the area is still needed to make a conclusion.
Read more about this topic: Cyclone Catarina
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