Rare South Atlantic Tropical Storm Off Coast Of Brazil

Satellite view of rare Tropical Storm Akara last Sunday
off the coast of Brazil 

The other day,  I told you about how forecasters are concerned that there might be a busy hurricane season in the Atlantic Ocean later this year.  

All those potential hurricanes would be in the North Atlantic, meaning north of the Equator. 

Meanwhile, below the Equator, a rare tropical storm blossomed this past Sunday in the South Atlantic. Tropical Storm Akará formed about 300 miles southeast of São Paolo.

As tropical storms go, Akará wasn't huge. It had top sustained winds of just 40 mph, just a little above the threshold to be considered a tropical storm. 

However, tropical storms are extreme rare off the coast of Brazil in the South Atlantic. Occasionally, you'll see a subtropical storm, which has characteristics of both a tropical storm and a regular storm.  A tropical storm has a warm core, fueled only by heat energy released from evaporation off of very warm ocean waters. 

 A regular storm has a cold core, fed by contrasts between warm air to the south and cold air to the north.  A subtropical storm usually is a cold core storm that encounters warm ocean water and begins to take on some - but not all - of the characteristics of a tropical storm.

As Yale Climate Connections reports, you get one or two subtropical storms in the South Atlantic each year. But Akará was only the third purely tropical storm off the coast of Brazil since at least 2010.

Ocean currents usually keep the South Atlantic too cool for purely tropical storms to develop. But sea surface temperatures where Akará formed were warmer than average - around 79 degrees - and that's barely warm enough for a tropical storm to get its act together. 

Yale Climate Connections reported that until around 2000, it was thought that subtropical or tropical storms couldn't form in the South Atlantic. That was mostly because upper level winds there blow wannabe storms apart before they can ramp up. 

But in 2004, an actual hurricane hit Brazil, causing three deaths and a lot of damage. Scientists then reviewed old satellite images and concluded that - at least in the era of satellites - subtropical storms do form off the coast of Brazil.

The history of pure tropical storms is more murky. So we can't really say whether everybody just missed tropical activity off the coast of Brazil over the decades, or oceans there have warmed up enough to support tropical storms and hurricanes. 

As for Akará, it moved south into colder waters and dissipated earlier this week.