All about hurricanes


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All about hurricanes

  2. 2. WHAT IS A HURRICANE? A hurricane is an intense, rotating oceanic weather system that possesses maximum sustained winds exceeding 119 km/hr (74 mph). It forms and intensifies over tropical oceanic regions.
  3. 3. HURRICANE FACTS  Hurricane season officially runs from June through November when the waters of the Atlantic Ocean are warm enough to produce a tropical cyclone, a category of weather systems that includes tropical depressions, tropical storms and hurricanes.  The centre is called the eye. In the eye of a hurricane there is a calm area of blue sky.  Around the eye there are very strong winds – a minimum speed of 120 kilometres per hour – accompanied by torrential rains.  Hurricanes cause more widespread damage than tornadoes because they are bigger – some as large as 1,000 kilometres across.  One of the most destructive effect of a hurricane is the storm surge, often causing serious flooding.
  4. 4. HURRICANE SEASON Every year, the world experiences hurricane season. During this period, hundreds of storm systems spiral out from the tropical regions surrounding the equa-tor, and between 40 and 50 of these storms intensify to hurricane levels. In the Northern Hemisphere, the season runs from June 1 to Nov. 30, while the Southern Hemisphere generally experiences hurricane activity from January to March. So 75 percent of the year, it's safe to say that someone somewhere is probably worrying about an impending hurricane.
  5. 5. HOW DO THEY BEGIN?  A hurricane builds energy as it moves across the ocean, sucking up warm, moist tro-pical air from the surface and dispensing cooler air aloft. Think of this as the storm breathing in and out. The hurricane escalates until this "breathing" is disrupted, like when the storm makes landfall. At this point, the storm quickly loses its momentum and power, but not without unleashing wind speeds as high as 185 mph (300 kph) on coastal areas.  http://science.howstuffworks. com/nature/naturaldisasters/hurricane.htm  HOW A HURRICANE WORKS VIDEO LINK
  6. 6. DEFINING A HURRICANE  To understand how a hurricane works, you have to understand the basic principles of atmospheric pressure. The gases that make upEarth's atmosphere are subject to the planet's gravity. In fact, the atmosphere weighs in at a combined 5.5 quadrillion tons (4.99 quadrillion metric tons). The gas molecules at the bottom, or those closest to the Earth's surface where we all live, are compressed by the weight of the air above them.  The air closest to us is also the warmest, as the atmosphere is mostly heated by the land and the sea, not by the sun. To understand this principle, think of a person frying an egg on the sidewalk on a hot, sunny day. The heat absorbed by the pavement actually fries the egg, not the heat coming down from the sun. When air heats up, its molecules move farther apart, making it less dense. This air then rises to higher altitudes where air molecules are less compressed by gravity. When warm, low-pressure air rises, cool, high-pressure air seizes the opportunity to move in underneath it. This movement is called a pressure gradient force.
  7. 7.  You never hear about hurricanes hitting Alaska. That's because hurricanes develop in warm, tropical regions where the water is at least 80 degrees Fahrenheit (27 degrees Celsius). The storms also require moist air and converging equatorial winds. Most Atlantic hurricanes begin off the west coast of Africa, starting as thunderstorms that move out over the warm, tropical ocean waters.-  A hurricane's low-pressure center of relative calm is called the eye. The area surrounding the eye is called the eye wall, where the storm's most violent winds occur. The bands of thunderstorms that circulate outward from the eye are called rain bands. These storms play a key role in the evaporation/condensation cycle that feeds the hurricane.
  8. 8. HURRICANE CATEGORIES  There are five categories of hurricanes, which are based on wind speeds. The categories help to make people aware of how much damage a hurricane may cause because the greater the wind speed, the more dangerous the storm. Category 1 – Winds 74 – 95 mph  Winds snap branches, uproot trees, and overturn mobile homes that aren't secured to the ground. Category 2 – Winds 96 -110 mph  Winds are strong enough to destroy weak doors and windows, and create 8-foot ocean waves. Category 3 – Winds 111 - 130 mph  Intense winds cause major flooding near the coast, which can destroy homes and businesses. Category 4 – Winds 131 - 155 mph  Winds are strong enough to destroy some buildings. Causes heavy damages to building roofs. Category 5 – Winds greater than 155 mph Buildings along the shorelines are washed away. Buildings can be completely destroyed. 
  9. 9. WHAT’S THE DIFFERENCE BETWEEN A HURRICANE WARNING AND A HURRICANE WATCH?  During a hurricane watch, there is the possibility that a hurricane will make landfall within 36 hours, and people are advised to prepare for a possible storm ahead. When a hurricane warning is issued, a hurricane is definitely on the way, and will make landfall within 24 hours.  The National Hurricane Center, located in Miami, Florida issues watches and warnings before hurricanes approach the coastline. They use computers with satellite images to figure out where and when a hurricane will come on shore.  Sometimes, if a hurricane is strong enough, officials may require citizens to evacuate, or leave their homes, and travel to a safer place.