Here's why a hurricane has never crossed the equator
Did you know that a hurricane or tropical storm has never crossed the equator? The reason behind this fascinating phenomenon lies in a meteorological principle related to the rotation of the Earth: the Coriolis force.
The Coriolis force is responsible for deflecting winds to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
"This force is what gives tropical systems their iconic swirl -- counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere," AccuWeather lead hurricane expert Alex DaSilva explained.
At the equator, however, the Coriolis force is essentially zero, making it impossible for a tropical system to cross over from one hemisphere to another.
Typhoon Vamei in 2001 was the closest storm to the equator
Most tropical systems remain north of 5 degrees north latitude or south of 5 degrees south latitude. The closest a tropical storm or hurricane has ever come to crossing the equator was Typhoon Vamei in December 2001 in the western Pacific, which got within 100 miles of the equator, forming at only 1.4 degrees North latitude.
An unnamed tropical depression in 1973 formed farther south
The closest a tropical depression has ever formed to the equator was an unnamed storm in December 1973. This storm formed at 0.5 latitude. It later became a tropical storm around 0.7 latitude, according to the China Meteorological Administration. The official record by the U.S. National Hurricane Center disagrees, saying it did not have tropical-storm-force winds until later in its path, north of 10 degrees north latitude. This is likely due to the different ways that the two agencies measure winds in a tropical system.
Another fact you may notice on the world tropical cyclone map is that there have been no tropical storms in the southeastern Pacific west of South America and few subtropical or tropical storms off the east coast of the continent.
Why are there so few tropical storms in the South Atlantic?
Only one hurricane has ever formed off the coast of South America: an unnamed storm locally called Catarina in 2004. According to the NHC, only two additional unnamed tropical storms have ever roamed the southern Atlantic basin, in 2010 and 2011. The other storms shown on the map above are subtropical storms, a designation for a cyclone with high winds that is not 100 tropical in nature.
Average sea-surface temperatures above the threshold for tropical storm development (26 C) between 1982 and 1995. The Peru Current brings cold water up the west coast of South America while the Brazil current brings warm water southward off South America's east coast. Adapted from app.earth-observer.org. (AccuWeather/NOAA WPC)
The lack of activity off the west coast of South America is primarily because of colder waters, DaSilva says. The Peru Current brings cold water northward along the coast. Another factor is higher wind shear, which tears apart most tropical storms before they can strengthen.
"The waters off Brazil are not as cold, because the offshore currents are from the north, but the wind shear is still too strong to support many tropical storms," DaSilva explained.
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