Hurricanes

Hurricanes - Nature 's Fury Unleashed

Hurricanes are some of the most violent weather systems on Earth and produce winds of enormous destructive power . They represent a truly monstrous force of nature : if we can imagine a huge system of stormy winds , about 500-mile wide , that releases energy equivalent to three 10-megaton nuclear bomb blasts every hour , we would have a good idea of the ferocious power of these unstoppable weather monsters . A typical hurricane can last for days , or even weeks , and can wreak devastation on mammoth scales in its unpredictably winding

and staggeringly windy path Wind speeds commonly exceed 33 meters per second (119km /h ) and , in the most intense hurricanes like Andrew , may reach 50 meters per second (180km /h . Hurricanes (or cyclones and typhoons as they are called in different parts of the world ) are a regular calamity in the tropics . It is estimated that on average 20 ,000 people perish annually owing to the wanton destruction unleashed by hurricanes , which make about 80 visitations to populated areas in a typical year in addition there would be untold losses to housing and property , natural vegetation (especially in agriculture-dependent areas ) and shipping (Digby 2001

Besides high winds , the destruction posed by hurricanes comes in the forms of storm surges and flooding . In fact , according to the National Hurricane Center , the greatest danger that a hurricane presents in terms of potential loss of life comes in the form of storm surges (NHC 2006 When the winds swirling around a storm forcefully push water in the sea toward the shore , they create a storm surge . An advancing surge acts on the normal sea tides to raise a hurricane storm tide , which can increase the mean water level 15 feet or more . The intensity of a storm tide is further exacerbated when wind-driven waves are superimposed on it . The resulting phenomenal rise in water levels can cause severe flooding in coastal areas , particularly when the occurrence of storm tide coincides with that of normal high tides . The havoc caused by storm tides is immensely boosted by the fact that a large percentage of the United States ' densely populated Atlantic and Gulf Coast coastlines lie less than 10 feet above mean sea level

However , while storm surges hold greater potential risk , in reality more people have died from inland flooding caused by hurricanes in the past few decades . Inland flooding can be a major threat to communities hundreds of miles from the coast as intense rain can result from the huge tropical air masses associated with a hurricane . Ironically , some of the greatest rainfall amounts occur from relatively weaker storms that drift slowly or hover over a particular area

A tropical storm is a large rotating area of very low pressure . Tropical storms form at sea . Hurricanes are these huge tropical storms with winds that blow faster than 74 miles per hour , packed with heavy rains and thunderclouds . A combination of trigger mechanisms , which rely on intensive rising convection or heat currents , are required to escalate a weather imbalance over vast areas covered by sea water into a more destructive hurricane . Hurricane development is initiated when upper air winds in the troposphere cause a rapid ascent of air which is sucked in from the sea surface to replace that lost above . Hurricanes arise as warm moist air over tropical waters rises above 6 ,000 feet (1800 m . As trade winds rush into the center of the storm , they spiral inwards and upwards releasing heat and moisture . The rotation of the Earth assists the rising columns of air , which soon begin to resemble a whirling cylinder around an eye of still , cloud-free descending air

The hurricane is continuously fed by energy stored in water vapor brought upwards by air from evaporation at sea level . As the air rises the water vapor condenses , turns to raindrops , releasing heat energy This heat in turn causes columns of air to rise up quickly (updraft ) to heights of 50 ,000 to 60 ,000 feet (18 ,000m ) and there result cauliflower-shaped cumulus clouds which act as thunderheads . The generation of heat continues to further the uplift and instability so long as the rising air is warmer than the surrounding air . Thus , the rapid upward draft of moisture-laden air produces huge volumes of condensation to form massive clouds . The huge amount of heat required to create and maintain the hurricane is reflected in the height of the clouds near its center , often up to 12 km in The center of a hurricane , called its eye , is a cloudless hole , usually about 10 miles (16 km ) wide , within which all is surprisingly calm and peaceful . But surrounding the eye , howling winds swirl at fantastic speeds . For days the monster thus generated spins ominously across warm tropical seas . If the waters along the hurricane 's path become warmer the storm may grow larger and stronger , posing graver potential threat when it hits land . The energy released within hurricanes is enormous it is estimated that a hurricane which hit Galveston , Texas , in September 1900 had sufficient energy to drive all the world 's power stations for four years . Incidentally , this is the deadliest hurricane on record in the United States and killed 6 ,000 people (Souza 1996

As soon as a fierce hurricane passes over cooler waters or crosses land it starts losing its might , and begins to break apart and die . When the hurricane reaches land it loses its supply of heat and moisture and therefore its energy source . It can quickly return to being a mere tropical storm or disturbance , especially when cold air is drawn in . It may be noted that an extensive ocean area with surface temperatures greater than 27 degrees centigrade for a significant period of time is a minimum prerequisite for the formation of hurricanes . Also , water which is turbulent or is likely to mix with cooler sources reduces the possibility of hurricanes . Hurricane formation is most common between 5 degree and 30 degree latitude

Hurricanes are classified using a disaster-potential scale developed in the 1970 by the U .S . National Weather Service (NWS ) as a measure to describe the potential for wind and storm-surge damage of a hurricane The Saffir /Simpson scale is used by the NHC and NWS to give public officials information on the destructive potential of a hurricane on landfall . It represents an estimate of what a hurricane could possibly do to a coastal area if it were to make a direct hit

According to this classification , category one hurricane is associated with winds of speed 74-95 mph , which can cause a storm surge of generally 4-5 feet above normal . No real damage to building structures would occur through the weaker hurricanes . Hurricane Lili of 2002 that made landfall on the Louisiana coast is an example of Category One hurricane . Considerable damage to mobile homes , poorly constructed signs , and piers can occur from a category two hurricane . Hurricane Frances of 2004 that made landfall over the southern end of Hutchinson Island , Florida , is an instance of category two . Category three is associated with wind speeds of 111-130 mph and storm surge of 9-12 ft above normal . Some structural damage to small residences may occur mobile homes could be destroyed . Hurricanes Jeanne of 2004 which made landfall in Florida is an example . Category four hurricane can cause extensive damage to doors and windows . An emergency evacuation of residential areas on low ground as far inland as 6 miles may be required . Hurricane Charley of 2004 , which made landfall in Charlotte County , Florida , is a category four hurricane

The final category five is associated with winds greater than 155 mph (249 km /hr , and storm surge levels greater than 18ft above normal . It can cause widespread destruction by blowing out roofs of many residences and buildings in its path . Massive evacuation of residential areas 5 to 10 miles into the interior of the shoreline may be required . Fortunately this category hurricanes are very rare . Many hurricanes that start as category five lose steam by the time of landfall . Hurricane Andrew of 1992 that made landfall over southern Miami-Dade County , Florida causing 26 .5 billion dollars in losses , is an infamous category five specimen . The most catastrophic hurricane in the recent years , Hurricane Katrina , was a strong category three storm on landfall at Buras Louisiana , but hit more vulnerable areas

In his book , Acts of God : The Unnatural History of Natural Disaster in America ' Steinberg points out that seven out of the ten most costly natural catastrophes in U .S history have been hurricanes , and have occurred since 1989 (Steinberg 2000 . As the effects of global warming become more pronounced , hurricane experts believe we are headed into a very active period for these unmitigated furies of nature , a period of more frequent and more devastating hurricanes

References

Digby , B . 2001 . Global Challenges . Oxford : Heinemann Educational Publishers

NHC . 2006 . Storm Surge . Hurricane Preparedness . National Hurricane Center . Retrieved

25 September 2006 from http /www .nhc .noaa .gov /HAW2 /english /storm_surge .shtml

Souza , D . M . 1996 . Hurricanes . Minneapolis , MN : First Avenue Editions

Steinberg , T . 2000 . Acts of God : The Unnatural History of Natural Disaster in America

Oxford : Oxford University Press ...