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South Atlantic tropical and subtropical cyclones
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South Atlantic tropical cyclones
South Atlantic tropical cyclones are unusual weather events that occur in the Southern Hemisphere. Strong wind shear in the Troposphere, which disrupts the formation of cyclones, as well as a lack of weather disturbances favourable for development in the South Atlantic Ocean make any strong tropical system extremely rare. The Intertropical Convergence Zone (ITCZ drops one to two degrees south of the equator, not far enough from the equator for the Coriolis force to aid development. Water temperatures in the tropics of the southern Atlantic are cooler than those in the tropical north Atlantic.
Hurricane Catarina in 2004 is the only recorded South Atlantic hurricane in history. Nevertheless, although infrequent, significant tropical and subtropical cyclones affect the Brazilian coastal states of Rio de Janeiro, Sao Paulo, and Santa Caterina during the months from November to May.
South Atlantic tropical cyclone
South Atlantic tropical cyclones are unusual weather events that occur in the Southern Hemisphere. Strong wind shear, which disrupts the formation of cyclones, as well as a lack of weather disturbances favorable for development in the South Atlantic Ocean make any strong tropical system extremely rare, and Hurricane Catarina in 2004 is the only recorded South Atlantic hurricane in history. South Atlantic storms have developed year-round, with activity peaking during the months from November through May in this basin. Since 2011, the Brazilian Navy Hydrographic Center has assigned names to tropical and subtropical systems in the western side of the basin, near Brazil, when they have sustained wind speeds of at least 65 km/h (40 mph), the generally accepted minimum sustained wind speed for a disturbance to be designated as a tropical storm in the North Atlantic basin. Below is a list of notable South Atlantic tropical and subtropical cyclones.
South Atlantic hurricane tracks Tracks of named South Atlantic tropical and subtropical cyclones since 2004 Theories concerning infrequency of occurrence
Until April 1991, it was thought that tropical cyclones did not develop within the South Atlantic. Very strong vertical wind shear in the troposphere is considered a deterrent. The Intertropical Convergence Zone drops one to two degrees south of the equator, not far enough from the equator for the Coriolis force to aid development. Water temperatures in the tropics of the southern Atlantic are cooler than those in the tropical north Atlantic.
During April 1991, these assertions were proven false, when the United States National Hurricane Center reported that a tropical cyclone had developed over the Eastern South Atlantic. In subsequent years, a few systems were suspected to have the characteristics needed to be classified as a tropical cyclone, including in March 1994 and January 2004. During March 2004, an extratropical cyclone formally transitioned into a tropical cyclone and made landfall on Brazil, after becoming a Category 2 hurricane on the Saffir-Simpson hurricane wind scale. While the system was threatening the Brazilian state of Santa Catarina, a newspaper used the headline "Furacão Catarina," which was originally presumed to mean "furacão (hurricane) threatening (Santa) Catarina (the state)". After international presses started monitoring the system, "Hurricane Catarina" has formally been adopted.
At the Sixth WMO International Workshop on Tropical Cyclones (IWTC-VI) in 2006, it was questioned if any subtropical or tropical cyclones had developed within the South Atlantic before Catarina. It was noted that suspect systems had developed in January 1970, March 1994, January 2004, March 2004, May 2004, February 2006, and March 2006. It was also suggested that an effort should be made to locate any possible systems using satellite imagery and synoptic data; however, it was noted that this effort may be hindered by the lack of any geostationary imagery over the basin before 1966. A study was subsequently performed and published during 2012, which concluded that there had been 63 subtropical cyclones in the Southern Atlantic between 1957 and 2007. During January 2009, a subtropical storm developed in the basin, and in March 2010, a tropical storm developed, which was named Anita by the Brazilian public and private weather services. In 2011, the Brazilian Navy Hydrographic Center started to assign names to tropical and subtropical cyclones that develop within its area of responsibility, to the west of 20°W, when they have sustained wind speeds of at least 65 km/h (40 mph).
Known storms and impacts
1991 Angola tropical storm
Tropical storm (SSHWS) 1991041215zVIS
1991 Angola Tropical Cyclone track
Duration April 10, 1991 – April 14, 1991 Peak intensity 65 km/h (40 mph) (1-min) A low pressure area formed over the Congo Basin on April 9. The next day it moved offshore northern Angola with a curved cloud pattern. It moved westward over an area of warm waters while the circulation became better defined. According to the United States National Hurricane Center, the system was probably either a tropical depression or a tropical storm at its peak intensity. On April 14, the system rapidly dissipated, as it was absorbed into a large squall line. This is the only recorded tropical cyclone in the eastern South Atlantic.
Hurricane Catarina was an extraordinarily rare hurricane-strength tropical cyclone, forming in the southern Atlantic Ocean in March 2004. Just after becoming a hurricane, it hit the southern coast of Brazil in the state of Santa Catarina on the evening of March 28, with winds estimated near 155 kilometres per hour (96 mph), making it a Category 2-equivalent on the Saffir-Simpson Hurricane Scale.
The storm developed out of a stationary cold-core upper-level trough on March 12. Almost a week later, on March 19, a disturbance developed along the trough and traveled towards the east-southeast until March 22 when a ridge stopped the forward motion of the disturbance. The disturbance was in an unusually favorable environment with a slightly below-average wind shear and above-average sea surface temperatures. The combination of the two led to a slow transition from an extratropical cyclone to a subtropical cyclone by March 24. The storm continued to obtain tropical characteristics and became a tropical storm the next day while the winds steadily increased. The storm attained wind speeds of 75 mph (equivalent to a low-end Category 1 hurricane on the Saffir–Simpson scale) on March 26. At this time it was unofficially named Catarina and was also the first hurricane-strength tropical cyclone ever recorded in the Southern Atlantic Ocean. Unusually favorable conditions persisted and Catarina continued to intensify and was estimated to have peaked with winds of 100 mph (155 km/h) on March 28. The center of the storm made landfall later that day at the time between the cities of Passo de Torres and Balneário Gaivota, Santa Catarina. Catarina rapidly weakened upon landfall and dissipated on the next day.
Since Catarina was the first tropical cyclone to make landfall in Brazil since the beginning of reliable records, and hence infrastructure and the population were not specifically prepared for it, the damage was quite severe. Catarina destroyed 1,500 homes and damaged around 40,000 others. Agricultural products were severely damaged: 85% of the banana crops and 40% of the rice crops were lost in the storm. Three people were confirmed to have perished in the storm and 185 others were injured. Damages from the storm amounted to US$350 million (value in 2004).