Friday 31st March, 2006
12:00 pm, M345 Building 28

 

CATARINA: THE FIRST DOCUMENTED SOUTH ATLANTIC HURRICANE AND ITS ASSOCIATION WITH VERTICAL WIND SHEAR AND HIGH LATITUDE BLOCKING

Alexandre Bernardes Pezza
School of Earth Sciences
The Univerity of Melbourne

It has been believed that hurricanes could not form over the South Atlantic Ocean due to a couple of main reasons, these being a very intense climatological vertical wind shear and not sufficiently warm SSTs. This concept has been consistently portrayed in text books and in the more specialized literature, being so strongly present in the day to day experience of the weather forecasters and climate researchers that it was difficult to accept that nature could present a different behavior.

At the end of March 2004 the cyclone Catarina hit Brazil. This was the first documented time when a system reaching a category I hurricane strength made landfall anywhere in the South Atlantic basin. This is not to say that a phenomenon like Catarina had not existed in the past, but there is very strong evidence that at least during the satellite era this is unprecedented.

A few important questions arise after March 2004. First, what Catarina really was and how should we refer to it? Second, was Catarina a result of natural climate variability only, or could it also be related to climate change due to anthropogenic influences?

Here, we show that the Catarina phenomenon, which was named after Saint Catarina State in Brazil (where landfall occurred), initiated off the Brazilian coast around the 20th of March 2004 as an EC, undergoing Tropical Transition three days later and reaching a category I hurricane strength under an unprecedented combination of low wind shear and strong mid-to-high latitude blocking. Emphasis is given to the large scale mechanisms associated with this event, and a possible link between the large scale anomalies and the increase in the positive phase of the most important mode of circulation in the Southern Hemisphere, the Southern Annular Mode (SAM), is discussed in terms of climate change and future Atlantic storms.