Severe Weather in Brazil

Tornados

There several conditions needed for the development of a tornado.  First, wind shear is needed to produce a rotating horizontal air mass.  Next, a thunderstorm's updraft is needed to lift the horizontal rotating air mass into the storm as a vertical air mass.  This is called a mesocylcone.  A funnel cloud may develop from the mesocyclone.  The funnel cloud emerges from the wall cloud and as soon as it touches the ground it is called a tornado.  Tornadoes travel with the storm system in the US typically a westward to eastward direction rotating counterclockwise due to the westerlies.

Brazil has experienced tornados mostly in the south and southeast regions.  It appears that much of the population believed tornados were very rare.  An official government tornado registry did not exist in 2011.  Weather enthusiasts have created sites in Brazil for citizens to self-report.  As a result, there was a 10-fold increase in tornados reported over the last decade.  Some attribute this to climate change other's say it's simply because of the accessibility to reporting mechanisms.

In the US, about 1,200 tornados are reported annually.  In comparison, only 5 "notable" tornados were listed on Wikipedia for Brazil.  Tornados are rare but not uncommon in Brazil. However, with the lack of an official registry, it's unclear as to the prevalence these events occur.

Here is an old outdated map created by the famous tornado researcher Fujita to give an idea of where tornado's usually occur on a global scale.  You can see that Brazil and Uruguay have several dots.  As you can see, most tornados occur in the Mid-Latitudes.

Source:  http://www.pbs.org/wgbh/nova/earth/tornado-country.html

My best guess as to why tornados have increased over time is because of an increase in population sprawling over a larger geographical area.  Taking this factor into consideration with an increase in technological communications, I believe more people are seeing and sharing tornado experiences than ever before.

Hurricanes

The three requirements for hurricane formation are deep warm ocean water, hot surface water to fuel evaporation and a Coriolis to initiate spinning.  Brazil's coastline extends along the South Atlantic ocean, which had never officially recorded a hurricane until 2004.  The conditions of the South Atlantic make hurricanes very rare.  The upper level winds are very strong, discouraging to storm development. Sea surface temperatures are colder, hot water is the fuel.  Finally, there's no convergence, ITCZ.  But in 2004 Cyclone Catarina took everyone by surprise.  A combination of unusual events occurred to produce this storm.  An upper level low was cut-off and then blocked by a stationary High. Lots of moisture traveling southeastward off the South American continent thus was also blocked, feeding strong thunderstorms in the Low pressure air mass over slightly cool water.

Cyclone Catarina
Source: https://courseware.e-education.psu.edu/public/meteo/Images/Section8/brazilcyclone_lowres0805.jpg

Hurricanes form in the regions illustrated in the graphic below. There are several names for tropical cyclones.  In the Northern Hemisphere near North America, they are called hurricanes.  In the North Pacific near Southeast Asia and India they are called Typhoons.  Lastly in the Southern Hemisphere they are simply called cyclones.

Source: http://www.learnnc.org/lp/editions/nchist-recent/6248

In the US, hurricanes in the Atlantic usually travel from low latitude eastern warm water toward midlatitudes traveling northwest, north, and even northeast.  They begin off the coast of North Africa fueled by prevailing winds and warm deep water once arriving at the Gulf Stream.  They swing northward and continue in that direction until flow from the Westerlies takes them north -northeast.

Hurricanes do not normally occur in Brazil. The average number of hurricanes to hit the US per year is about 1.72 per year. As described above, only Cyclone Catarina has ever been recorded to strike Brazil.