A Rare Tropical Storm in the South Atlantic

A Rare Tropical Storm in the South Atlantic

Tropical storms seldom roam in the South Atlantic Ocean. But in mid-February 2024, one such storm formed off the coast of Brazil.

The disturbance began to develop as a stalled front of low pressure on February 15. According to researchers at NOAA’s Cooperative Institute for Meteorological Satellite Studies (CIMSS), the front formed into a subtropical depression on February 16 after being fed by a plume of tropical moisture that plunged south. The depression continued to intensify and move south, and at 9 p.m. local time on February 18 (00:00 Universal Time on February 19) the Brazilian Navy Hydrographic Center upgraded it to Tropical Storm Akará. At the time, the storm carried sustained winds of up to 64 kilometers (40 miles) per hour.

The MODIS (Moderate Resolution Imaging Spectroradiometer) instrument on NASA’s Aqua satellite captured this image of Akará around 2:20 p.m. local time (17:20 Universal Time) on February 19, 2024, when its center was about 900 kilometers (560 miles) southeast of São Paulo.

Until the start of the 21st century, tropical cyclones in the South Atlantic were undocumented. According to meteorologists at Yale Climate Connections, wind shear was often too high for storm formation, and easterly waves from northern Africa—which seed cyclones and hurricanes in the Atlantic—are not a regular occurrence south of the equator.

In 2004, a rare tropical cyclone formed in this region and eventually made landfall in Brazil’s southern state of Santa Catarina. The National Hurricane Center in Miami estimated the storm was a category I hurricane (named Catarina), making it the first hurricane in the South Atlantic in the satellite record. At the time, the Brazilian Center for Weather Prediction did not operate any anemometers (wind measuring devices) in the area or have any hurricane hunter aircraft to fly through the storm. All estimates were based on satellite data only.

After Catarina, forecasters paid closer attention to storm development in the South Atlantic. Since 2015, three other tropical storms have been recorded in the basin: Tropical Storm Iba in 2019, Tropical Storm 01Q in 2021, and now Akará in 2024.

Warm sea surface temperatures likely contributed to Akará’s formation. According to Yale Climate Connections: “Sea surface temperatures in the vicinity of Akará on Monday were around 0.5 degrees Celsius warmer than average, at around 26 degrees Celsius (79 degrees Fahrenheit), or what’s typically considered to be the minimum threshold for tropical development.” This unusually warm water is more typical of temperatures in early summer, they noted, continuing a trend of warm sea surface temperatures that has persisted for months.

Akará is expected to remain well offshore and not have major impacts on land, aside from high surf along the coast south of Rio de Janeiro. Forecasts show the storm weakening as it heads south over cooler waters.

NASA Earth Observatory image by Lauren Dauphin, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Story by Emily Cassidy.

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