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Hurricanes, Typhoons and Cyclonic Storms
Tropical cyclones are known by specific names in regions around the world, depending on where the storm develops and hits land. In the North Atlantic, Northeast Pacific Ocean and South Pacific Ocean, these storms are called hurricanes. Strong tropical cyclones in the Northwest Pacific Ocean are called typhoons. Severe cyclonic storms plague the North Indian Ocean. Severe tropical cyclones occur in the Southwest Pacific or the Southeast Indian Ocean. Finally, those storms which hit land in the Southwest Indian Ocean are called tropical cyclones.
The term tropical cyclone is a generic term used to describe a non-frontal, low-pressure system developing over tropical water with “organized convection” and “definite cyclonic surface wind circulation”, according to the National Oceanic and Atmospheric Administration. Organized convection means the storm is considered a thunderstorm.
The Coriolis Force at the Equator
Cyclonic surface wind circulation depends on the Coriolis Force involved. The Coriolis Force is the deflection of air once it begins to move caused by the earth’s rotation. In general this mean, objects in the Northern Hemisphere rotate to the right and objects in the Southern Hemisphere deflect to the left. The Coriolis Force at the equator is considered zero. Tropical cyclones cannot develop directly at the equator, as there is not Coriolis Force to help in deflection of air.
How Do Tropical Cyclones Form?
The University of Illinois Atmospheric Sciences Department has determined several factors needed in the creation of tropical cyclone formation.
- Warm ocean waters of 80 degree Fahrenheit or warmer
- Coriolis Force or some distance from the equator
- A weak organized disturbance to grow from
- Convection, like a thunderstorm
- Moisture throughout all layers of the atmosphere
- Low vertical wind shear, or low wind changes due to height
Tropical cyclones require warm, moist air to create energy for the storm development and to drive the cyclone circulation.
Storm Surge From Tropical Cyclones
Tropical storms are known for devastating storm surge, especially since these storms hit tropical areas with elevations at or below sea level. Storm surge is an onshore rush of the ocean or sea water caused by high winds and low-pressure from the storm. Strong winds help blow the water towards the shore. The low-pressure of the atmosphere within the storm causes the sea level to rise around the edges of the storm.
On November 16, 2007, a strong tropical cyclone, Cyclone Sidr, caused massive damage, killing over 3,000 people in Bangladesh. With winds over 150 mph, storm surge was inevitable, flooding the low-lying areas of the nation and surrounding islands. The storm surge reached heights of 4 feet, easily sweeping through the region. This storm was called a tropical cyclone as it originated in the Southwest Indian Ocean, increasing its strength over the Bay of Bengal, finally making landfall in Bangladesh and India.