Sunday, March 11, 2012

Facts About Hurricanes - The Swirling Storms of the Seas

Hurricane, the word is derived from Spanish word, "Huracan" which is a further derivation of word "Juracan" a god of storm. For a layman every swirling thunderstorm which strikes the land is a hurricane or typhoon as people, in most cases come to know such terms in the news. However, in order to learn the difference, we have to learn few basic concepts of the tropical cyclones. Hurricanes, typhoons, tropical depressions, cyclones and tropic storms are all the derivative names for Tropic Cyclones, depending on their strength, size and location. These storms or cyclones are characterized by strong winds, low-pressure centers and heavy rains.
A hurricane can be differentiated from tropical depression or thunderstorm on the basis of its strength, location and concentration. Depressions or storms usually generate winds less than 34 knots, and they have no eye. Whereas, hurricanes and typhoons are moving storm systems with the minimum wind speed of 66 knots or 119 km per hour, which is potentially devastating. A cyclone of such intensity develops an eye, an area in the centre of system having lowest atmospheric pressure. This eye is surrounded by the Eyewall, which can cover an area of 16 to 80 kms and play havoc. Maximum speed of hurricanes has been estimated to around 314 km per hour.
Hurricanes develop usually due to the formation of favorable atmospheric conditions around disturbance in the atmosphere. Natural phenomenon like El-NiƱo, Madden-Julian oscillation and Atlantic Multi-decadal oscillation modulate the background environment. Tropical systems, once born are moved by fast winds in troposphere under favorable conditions. As the systems move it tends to develop an eye. However, if the atmospheric conditions do not allow, the system gets weak and dissipates. Presently, technology has not been advanced enough to artificially induce dissipation of such storms or a hurricane.
Atmospheric pressure recorded at the center of hurricanes or the eye is lowest occurring on sea level surface of the world. Condensed latent heat, when released in large amounts, drives the hurricanes and it happens when moist air lifts up condensing its water vapors. The said heat distributes around the storm's center in a vertical order. Due to this, temperatures inside the hurricanes are usually warmer than the surrounding area.
The eye of a hurricane should not be taken in literal meanings. It is usually 30 to 120 km in diameters, though smaller hurricanes carry as small as an eye in diameter of 3 km and as large as 360 km. The environment inside the eye is usually calm and mild compared to its surrounding fast moving winds.
Hurricanes produce extremely devastating winds and storm surges. As they receive their energy from warmer oceanic waters, they tend to lose energy when they move on land as they also face greater surface friction in addition to the absence of warmer water. For the same reason, hurricanes render more damage to coastal or tropic regions than inland areas. Hurricanes can be lethal at coastal regions going as deep at 1000 kms, whereas it can also cause flooding up to 40 kms from coastline. Size of a hurricane can be classified into three main categories. Hurricanes ranging under 222 kms in radius are termed as "very small", those ranging from 333 to 670 km in radius are termed as "Average" and those greater in radius than 888 kms are classified as "Very large" hurricanes.
A difference between a typhoon and hurricane should be understood to avoid confusion. Severe tropic cyclones, when born in Northwestern Pacific and obtains high intensity wind speed, it is called a typhoon. On the other hand, a tropic cyclone which takes birth in Northeast Pacific basin or Atlantic Ocean is called a hurricane. Storms arising from the Southern hemisphere and Indian Oceans are simply called the Cyclones.
"Bhola Cyclone" at the coasts of Bangladesh in 1970 has been recorded as the deadliest one in recorded history in which nearly 0.3 million lost their lives. Another destructive hurricane is Hurricane Katrina in USA, which killed around 2,000 people and rendered an estimated property loss of 100 Billion $. Typhoon Tip which arose in 1979 in Pacific Ocean has been the most intense hurricane having the pressure of 870 mbar and wind speeds of 310 km/ hour. Tip was also the largest cyclone with the storm force winds active in 2170 km diameter. Hurricane John holds the record of longest lasting hurricane, which lasted for a full month in 1994 in the northern hemisphere.

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