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Hurricanes

By Janine Philips

November 9, 2014

Table of Contents:

- Hurricanes: Nature’s Stormy Wrath Unleashed
- How hurricanes
  begin
- Measuring hurricanes
- Where hurricanes are more likely to occur
- What makes hurricanes so damaging
- Extreme hurricanes during the past ten years



Hurricanes: Nature’s Stormy Wrath Unleashed 

Heavy rains, strong winds, big masses of clouds swirling around a center: these are the trademarks of hurricanes that come to town. Not only that, they can wipe off entire towns from the map and leave watery destruction in their wakes.
But what are hurricanes? How are they formed? Why are they so destructive?
Hurricanes are storms with sustained winds of at least 74 miles per hour. They are also known as cyclones in the Indian region or typhoons on the Pacific Region.

How hurricanes begin
Hurricanes are born from low pressure areas on the tropics where the water is at least 80 degrees Fahrenheit (27 degrees Celsius). When warm, low pressure air from the surface of the ocean rises rapidly, the cool, high pressure air moves underneath it. As the warm air rises, the water vapor that it brings condenses into clouds and rain. The condensation releases heat, warming the cool air and causing it to rise. The process repeats, pulling warm, moist air and dumping heat from the ocean surface into the atmosphere. The cycle goes on and on, creating the circular wind pattern and the big mass of clouds swirling around a center as seen in weather satellite images on TV.

Source: <http://cache.boston.com/universal/site_graphics/blogs/bigpicture/hurricane_09_08/hurricane8.jpg>
 
Winds at the surface collide and propel the warm moist air upward, reinforcing the wind that’s already rising to the top. Strong winds blowing at high altitudes further remove the rising hot air from the center of the storm. This sustains a repeated movement of warm air from the surface of the ocean.
Above 30,000 feet or 9,000 meters up in the atmosphere, high pressure air from the center of the storm takes away heat from the rising air. High pressure air is pulled to the low pressure part of the storm, driving the air cycle further and creating the ferocious winds associated with hurricanes.
A hurricane does not suddenly form. Rather, it starts as a tropical disturbance, a low pressure system with a defined wind circulation. Like a living organism, hurricanes need “food” in the form of warm, moist air in order to grow. It also needs optimal wind and pressure conditions to keep growing. A tropical disturbance must undergo three stages before it becomes a hurricane:
Tropical Depression – when wind speeds are less than 38 mph
Tropical Cyclone – when wind speeds are between 39 mph to 73 mph
Hurricane – when wind speeds are greater than 74 mph

Measuring hurricanes
Meteorologists use weather satellites to see developing hurricanes from outer space, track their location and direction, and estimate their wind speeds. They depend on rating scales to classify hurricanes and to better prepare people for the incoming hurricanes. American meteorologists use the Saffir-Simpson Hurricane Scale. According to this scale, hurricanes are divided into five categories:
Category 1
Hurricanes in this category have wind speeds of 74-95 mph (119-154 km/h) and storm surges of 4-5 ft (1.2-1.5 meters). Category 1 hurricanes may cause some flooding, with little or no structural damage.
Category 2
Hurricanes in this category have wind speeds of 96-110 mph (155-178 km/h) and storm surges of 6-8 ft (1.8-2.4 meters). Category 2 hurricanes flood coastal roads, uproot trees, and rip shingles off the roofs.
Category 3
Hurricanes in this category have wind speeds of 111-130 mph (179-210 km/h) and storm surges of 9-12 ft (2.7-3.7 meters). Category 3 hurricanes cause severe flooding and some structural damage.
Category 4
Hurricanes in this category have wind speeds of 131-155 mph (211-250 km/h) and storm surges of 13-18 ft (3.9-5.5 meters). Category 4 hurricanes cause severe flooding reaching inland and major structural damage.
Category 5
Hurricanes in this category have wind speeds greater than 155 mph (250 km/h) and storm surges greater than 18 ft (5.5 meters). Category 5 hurricanes cause floods reaching farther inland and serious damage to most infrastructures.
Category 5 hurricanes are the most powerful and the most destructive. [1][2]

Where hurricanes are more likely to occur 
Hurricanes, cyclones or typhoons happen more frequently in warm, tropical regions near the equator where there is plenty of warm, moist air for hurricanes to form and grow.
In the United States, the states affected are those that are located in the tropical regions and nearest to the Atlantic Ocean. The areas that are the most susceptible to typhoons are: Tampa-St. Petersburg area and Miami in Florida, New Orleans, Louisiana (which was hardest hit by Hurricane Katrina), Norfolk and Virginia Beach in Virginia, Houston and Galveston in Texas. [3]
Elsewhere in the world, hurricanes coming from the Pacific Ocean strike the countries that are located on or nearest to it. Examples are Polynesia, the Philippines, Vietnam, China, and Japan.

What makes hurricanes so damaging
The most damaging and life threatening aspect of hurricanes are not the very strong winds, but the storm surges and floods.
Storm surges happen when strong winds during hurricanes create huge waves that flood the coastlines. Storm surges are not the only contributors of floods during hurricanes. Hurricanes dump months’ worth of rain even in areas far from bodies of water, flooding those areas. Those rains also fill rivers to overflowing, damaging the riverbanks.
The damage caused by the ferocious hurricane winds is little compared to the damages caused by the storm surges and the floods. While the winds can rip shingles off roofs and uproot trees, floods and storm surges can inundate and wipe out entire villages and towns, causing billions of dollars in damage and numerous fatalities.

Extreme hurricanes during the past ten years
Many hurricanes form and make landfall every year. But there are some hurricanes that have certainly made their mark. All hurricanes are destructive, but some hurricanes have claimed more lives and done more damage than the average hurricane.
Superstorm Sandy made landfall on the US in 2012. It had 129 km/h winds and caused 234 deaths and $65 billion in damage.
Hurricane Katrina hit the US in 2005 with sustained winds gusting at 201 km/h. Hurricane Katrina took away the lives of 1,833 people and caused $147 billion in damage.
Hurricane Ike struck United States, the Bahamas, Turks and Caicos, and Cuba on 2008, causing 195 deaths and $32 billion damages in total.
In the Philippines, Supertyphoon Haiyan made landfall in 2013 and caused 2,500 estimated deaths and $14 billion in estimated damage. It was considered the most powerful typhoon ever recorded, with sustained winds estimated at 314 km/h. [4] [5]


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References:

[1] Brain, Marshall, Craig Freudenrich, Ph.D. and Robert Lamb.  "How Hurricanes Work"  25 August 2000.  HowStuffWorks.com. <http://www.howstuffworks.com/nature/natural-disasters/hurricane.htm>  24 June 2014.
[2] “What is a Hurricane?” Weather.com. <http://www.weather.com/outlook/weather-news/hurricanes/articles/hurricane-what-is-a-hurricane_2010-05-24> 24 June 2014
[3] Freedman, Andrew. “Top 5 Most Vulnerable Cities to Hurricanes” 16 June 2012. ClimateCentral.org <http://www.climatecentral.org/news/top-5-most-vulnerable-us-cities-to-hurricanes/> 25 June 2014.
[4] Toothman, Jessika, and Nicholas Gerbis.  "10 Most Destructive Storms"  12 May 2008.  HowStuffWorks.com. <http://science.howstuffworks.com/nature/climate-weather/storms/most-destructive-storms.htm> 24 June 2014.
[5] Walsh, Bryan. “The Typhoon’s Toll” 25 November 2013. Time. Vol. 182, No. 22. 2013. Pages 25-33.