A rare tropical storm develops in the South Atlantic Ocean near Angola; the first to be documented by satellites.
The South Atlantic Ocean is, by meteorological standards, an unlikely stage for the dramatic display of tropical cyclones. Unlike the bustling hurricane corridors of the North Atlantic or the Pacific, these powerful weather systems are exceptionally rare in the Southern Hemisphere's Atlantic basin, making their occasional appearance a subject of considerable scientific interest and local concern.
The Enigma of South Atlantic Tropical Cyclones
The scarcity of tropical cyclones in the South Atlantic can be attributed to a confluence of atmospheric and oceanic conditions that are generally unfavorable for their formation and intensification. One primary deterrent is the prevalent presence of strong wind shear. This phenomenon describes a significant change in wind speed or direction with altitude, effectively tearing apart the vertical structure of budding storms before they can properly organize and strengthen. Imagine trying to build a tall, stable tower while strong, unpredictable gusts are constantly pushing it from different directions; that's essentially what wind shear does to a forming cyclone.
Furthermore, the South Atlantic typically lacks the robust, pre-existing weather disturbances that often serve as the "seeds" for tropical development in other basins. There isn't a consistent equivalent of the Intertropical Convergence Zone (ITCZ) or the easterly waves that fuel many North Atlantic hurricanes. Coupled with generally cooler sea surface temperatures compared to other tropical basins, and the intrusion of dry air, these factors create an environment where the delicate conditions required for cyclogenesis rarely align.
Despite these formidable obstacles, history has recorded instances of these unusual weather events. The most notable and, indeed, the only officially recorded South Atlantic hurricane in history was Hurricane Catarina in 2004. This astonishing system defied all expectations, making landfall in the southern Brazilian state of Santa Catarina, causing significant damage and loss of life. Its unexpected formation and intensification profoundly challenged existing meteorological paradigms and underscored the potential, however rare, for such powerful storms in the region. Catarina remains a powerful reminder of nature's unpredictable force and the critical need for vigilance even in seemingly safe areas.
When and Where They Occur
While exceptionally rare, South Atlantic tropical and subtropical systems have demonstrated the ability to develop year-round. However, observational data indicates that activity, though sparse, tends to see a slight uptick during the months from November through May. This period aligns with the Southern Hemisphere's summer and autumn, when oceanic waters are warmest and atmospheric conditions might, on occasion, become marginally more conducive for cyclonic development.
Naming and Monitoring Efforts
Recognizing the potential for these rare but impactful events, the Brazilian Navy Hydrographic Center took a significant step in 2011. Since then, they have proactively assigned names to tropical and subtropical systems that develop in the western side of the basin, particularly near the eastern coast of Brazil. A system receives a name once its sustained wind speeds reach at least 65 km/h (40 mph). This threshold is widely accepted as the minimum sustained wind speed for a disturbance to be officially designated as a tropical storm, mirroring the criteria used by agencies in the North Atlantic basin.
This localized naming convention is a crucial initiative for enhancing public awareness, improving communication during potential threats, and streamlining disaster preparedness efforts within Brazil. While these names are not universally recognized by international meteorological bodies in the same way as those in more active basins, they serve a vital purpose in providing clear, actionable information to affected communities.
The study and monitoring of South Atlantic tropical and subtropical cyclones continue to be important for advancing our understanding of global weather patterns and for ensuring the safety of coastal populations in this unique corner of the world.
Frequently Asked Questions
Why are tropical cyclones so rare in the South Atlantic Ocean?
Tropical cyclones are rare in the South Atlantic due to a combination of strong wind shear, which disrupts storm formation; a general lack of pre-existing weather disturbances that can act as "seeds" for development; and comparatively cooler sea surface temperatures in key areas. These factors collectively create an environment largely unfavorable for sustained cyclogenesis.
Has a full-fledged hurricane ever occurred in the South Atlantic?
Yes, Hurricane Catarina in 2004 is the only officially recorded hurricane in the South Atlantic basin. It was an extraordinary event that made landfall in Brazil, causing significant damage, and its formation profoundly impacted meteorological understanding of the region.
Are South Atlantic tropical systems given names?
Yes, since 2011, the Brazilian Navy Hydrographic Center has assigned names to tropical and subtropical systems that reach sustained wind speeds of at least 65 km/h (40 mph) in the western South Atlantic, particularly near Brazil's coast. This naming helps with local communication and preparedness.
When is the peak season for South Atlantic storms?
While South Atlantic storms can develop year-round, activity tends to peak during the Southern Hemisphere's warm season, specifically from November through May. This period generally offers slightly more favorable, albeit still challenging, atmospheric and oceanic conditions.
What is the difference between a tropical and a subtropical cyclone in this context?
A tropical cyclone derives its energy primarily from the heat released when moist air condenses, forming a warm core. A subtropical cyclone has characteristics of both tropical and extratropical storms, often having a broader wind field and a cooler core in its upper levels, deriving energy from both latent heat release and temperature differences. Both types are monitored and named by the Brazilian Navy if they meet the wind speed criteria.