On August 18, NOAA's GOES-West satellite captured an image of tiny Tropical Storm Karina followed to the east by the massive Tropical Depression12-E.
Image Credit: NASA/NOAA GOES Project
Tropical cyclones are essential features of the Earth's atmosphere. They transfer heat and energy between the equator and the cooler regions near the poles. A tropical cyclone is rotating system of clouds and thunderstorms that originate over tropical or sub-tropical areas, with organised convection ( thunderstorm activity) and winds at low levels circulating either anti-clockwise (in the northern hemisphere), or clockwise (in the southern hemisphere).
The whole storm system may be five to six miles high and 300 to 400 miles wide, although sometimes can be even bigger. It typically moves forward at speeds of 10-15 m.p.h., but can travel as fast as 40 m.p.h. At its very early and weak stages it is called a Tropical Depression. When the winds reach 39 m.p.h. it is called a Tropical Storm. If the wind should reach 74 m.p.h. or more the tropical storm is called a Hurricane in the Atlantic and the eastern North Pacific or a Typhoon in the western North Pacific. In other parts of the world, such as the Indian Ocean and South Pacific the term Cyclone or Tropical Cyclone is used.
Where Do Tropical Cyclones Occur?
Tropical cyclones form between approximately 5° and 30° latitude and initially move westward, affected by the easterlies movement, and slightly towards the poles. Many tropical cyclones eventually drift far enough from the equator to move into areas dominated by westerlies, especially in the middle latitudes. The westerlies tend to reverse the direction of the tropical cyclone to an eastward path. As the tropical cyclone moves polewards it picks up forward speed and may reach 30 m.p.h. or more. An average tropical cyclone can travel about 300 to 400 miles a day, or about 3,000 miles before it dies out.
Map: Areas of the world affected by tropical cyclones.
Image Credit: Met Office
Tropical cyclones that occur in the Atlantic region, affect the Caribbean and USA and comprise less than 15% of global tropical cyclone activity. Tropical cyclones also occur in various parts of the Pacific Ocean, and can affect coastal regions of Mexico, south-east Asia, north-east Australia and the south Pacific islands. Those that form in the Indian Ocean can affect India, Bangladesh, north-west Australia, some parts of east Africa and Indian Ocean islands such as Mauritius and Madagascar.
What are Extratropical Cyclone?
Extratropical cyclones sometimes called mid-latitude cyclones or wave cyclones, are a group of cyclones defined as synoptic scale low pressure weather systems that occur in the middle latitudes of the Earth (outside the tropics) not having tropical characteristics, and are connected with fronts and horizontal gradients in temperature and dew point otherwise known as "baroclinic zones". Extratropical cyclones are the everyday phenomena which, along with anticyclones, drive the weather over much of the Earth, producing anything from cloudiness and mild showers to heavy gales and thunderstorms.