It also revels a very interesting fact. None of them has ever crossed the equator. But why?
Tropical cyclones—known as hurricanes in the Atlantic and Northeast Pacific, typhoons in the Northwest Pacific, and simply cyclones in the South Pacific and Indian Ocean (see map here) —have never been observed to cross the equator.
This phenomenon is primarily due to the Earth’s rotation and the resulting Coriolis effect, which is essential for the formation and maintenance of these storms.
Reasons Why Tropical Cyclones Don’t Cross the Equator:
Coriolis Effect is Zero at the Equator:
- The Coriolis effect arises from the Earth’s rotation and causes moving air to deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
- At the equator, the Coriolis force is essentially zero. This means there is no force to initiate or maintain the rotation of a cyclone.
- Reference: National Oceanic and Atmospheric Administration (NOAA) states, “Because of the lack of Coriolis force at the equator, tropical cyclones rarely form within 5 degrees of the equator.”
Opposite Rotation in Different Hemispheres:
- Cyclones rotate counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere due to the Coriolis effect.
- Crossing the equator would require a cyclone to reverse its rotation, which is dynamically unfavorable and practically impossible.
- Reference: The American Meteorological Society explains, “The reversal of the Coriolis parameter at the equator inhibits tropical cyclones from crossing it.”
Lack of Supporting Wind Patterns:
- The Intertropical Convergence Zone (ITCZ) near the equator has prevailing winds that do not favor the movement of cyclones across the equator.
- The atmospheric conditions are not conducive to supporting the structure of a cyclone in this region.
- Reference: World Meteorological Organization notes, “The general circulation near the equator does not support the development or movement of tropical cyclones across it.”
Additional Information:
- Formation Latitude: Tropical cyclones typically form between 5 and 20 degrees latitude north or south of the equator.
- Rare Near-Equator Storms: While extremely rare, there have been instances of cyclones forming close to the equator but none have been documented to cross it.
- Dynamic Constraints: The physical laws governing atmospheric motion make it highly unlikely for a cyclone to survive the crossing even if it somehow reached the equator.
The absence of the Coriolis effect at the equator, the requirement for cyclones to reverse rotation when crossing hemispheres, and unfavorable wind patterns all contribute to why hurricanes and typhoons do not cross the equator.
These dynamic atmospheric conditions make it practically impossible for such storms to maintain their structure and energy while crossing.
You can also watch a video of every storm below:
Y.D. Robinson says
If one notices carefully, these tropical super-storms are quite rare in South America, certainly off the west coast where the cold Humboldt Current flows almost to the equator, but even off the east coast where the currents through the tropics anyway are warmer. It’s the eastward bulge of South America that steals most of the potential cyclone-forming warm currents away from South America and instead towards North America.
Also, due to the cold Benguela Current, there aren’t any cyclones forming off the west coast of southern Africa.