A tropical cyclone is a low pressure storm system with very strong winds and high rainfall. A tropical cyclone has numerous low pressure thunderstorms that form around a central point called an eye. Tropical cyclones usually form in areas that have warm and moist air and water, such as the equator.  In North and South America, these storms are most commonly called hurricanes. In the Indian Ocean and South Western Asia and Oceania region they are commonly referred to as cyclones. And in Eastern Asia they are referred to as a typhoon. Even though they all have different names, they are all categorized under the same type of storm, the tropical cyclone.
How tropical cyclones form
A tropical cyclone needs a "fuel" to grow and strengthen. That "fuel" is warm moist air. For that reason, we only see these storms in areas around the equator. Warm air generally rises from the surface upwards and this leaves a displacement affect area near the surface where the warm air once was. Higher pressure air from around the storm pushes into the lower pressure zone near the surface, and eventually warms up and rises itself. After the warm air rises into the atmosphere, it cools off and forms into clouds. This process is continued till the air and clouds swirl and become more violent. The system will continue to grow and spin as long as it has warm moist air and water feeding it. Once it hits colder water/air and/or it hits landfall, it will slowly lose its power and speed and start to become just a regular storm. 
Hurricanes originate in the Atlantic basin, which includes the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico, the eastern North Pacific Ocean, and, less frequently, the central North Pacific Ocean. A six-year rotating list of names, updated and maintained by the World Meteorological Organization, is used to identify these storms.  Hurricanes that form north of the equator spin counter-clockwise. This is because of the Coriolis force and Earth's rotation on its axis. The Atlantic hurricane season usually occurs between June 1st and November 30, sharply peaking from late August through September.  When a storm's maximum sustained winds reach 74 mph, it is called a hurricane. The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based on a hurricane's sustained wind speed. This scale estimates potential property damage. Hurricanes reaching Category 3 and higher are considered major hurricanes because of their potential for significant loss of life and damage. 
In Eastern Asia, tropical cyclones are referred to as typhoons. Because typhoons form north of the equator, they spin counter-clockwise.  This is because of the Coriolis force and Earth's rotation on its axis. Typhoons are the most active type of tropical cyclone in the world. If a typhoon hits 150 miles per hour (241 kilometers per hour) — as Haiyan did — then it becomes designated a super typhoon. Typhoon seasons occur at different times depending on the area in the Pacific. In the northeastern Pacific, the official season runs from May 15 to November 30, while in the northwestern Pacific, the typhoon season is most common from late June through December.  The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based on a typhoon's sustained wind speed. This scale estimates potential property damage. Typhoons reaching Category 3 and higher are considered major storms because of their potential for significant loss of life and damage.
In the Indian Ocean, Oceania and South Western Asia region tropical cyclones are commonly referred to as cyclones. Because cyclones form south of the equator, they spin clockwise.  This is because of the Coriolis force and Earth's rotation on its axis. Cyclones are large organized storms with well-defined cores that begin over tropical or subtropical waters, often as a result of monsoon troughs and easterly waves.  Cyclones in the Indian Ocean usually occur from the months of April to December.  In order for it to be categorized as a cyclone, its average sustained wind speed needs to exceed 63 km per hour. To be classified as severe, the average sustained wind speed needs to exceed 118 km per hour. 
Effects on humansTropical cyclones effect people all over the world. The hurricanes, typhoons and cyclones cause flooding, wind, rain, and erosion damage that can be severe to coastal areas. These storms have caused entire towns and communities to be lost due to damage. Many people have lost lives and possessions due to tropical cyclones. Some areas are better prepared to deal with these storms than others. Places that have had and face the greatest economic and physical losses from tropical cyclones are affluent countries with advanced infrastructures. Future tropical cyclone risk will increase due to global warming, population growth, urbanization, and increasing coastal settlement. 
Categories of storms
There are different categories of tropical cyclones depending on the wind speed of the storm. Tropical cyclones are given different names to show how fast their winds are. A storm that is less than 39 mph is designated as a tropical depression. When a storm reaches 39 mph to 74 mph it is officially called a tropical storm.  When it reaches 74 mph and higher, it is called a tropical cyclone.  People that study tropical cyclones like scientists and meteorologists use this scale to determine how much damage a particular storm could do to an area.
August 29, 2005, was the date Hurricane Katrina struck the coast of much of the southern United States, and most significantly, New Orleans, Louisiana. On that day, Hurricane Katrina made landfall in New Orleans and breached the levees of the city. An estimated 1,833 people died in the hurricane and the flooding, but the exact number is still unknown.  The breaching of the levees caused extreme water, wind and rain damage that destroyed more than one million homes and businesses. Katrina was by far the most destructive storm to strike the United States. It caused approximately $108 billion in damage. 
Hurricane SandyBetween October 24 and October 31 of 2012, a storm that would come to be known as Super Storm Sandy ripped through much of the Caribbean and the east coast of the United States. Damage from Sandy was done by flooding, wind and erosion. Sandy caused flooding, downed power lines and trees, and caused infrastructures to get demolished. On the day the storm hit the New Jersey/New York Metro area, there was a culmination of the perfect circumstances. The Moon on that day was full Moon, which meant that high tides were twenty percent higher than they normally would be, which significantly added to the flooding that would have happened without it. Sandy would end up causing about $20 billion in property damage alone. Also, it caused between $10 billion and $30 billion in lost business, making it one of the costliest natural disasters on record in the United States. 
Other closely related articles in this wiki include:
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- Hurricanes 101 Video - By National Geographic
- National Hurricane Center - By NOAA
- About Tropical Cyclones - By Australian Bureau of Meteorology
- Tropical Cyclone Climatology - By NOAA
- Hurricane Facts and Information - By National Geographic
- About Hurricane Katrina - By History.com