What Are Tropical Storms? Severe storms spawned in the tropics are known by different names in different parts of the world: hurricanes in the Atlantic and east Pacific and typhoons in the northwest Pacific and cyclones in the southwest Pacific and Indian Ocean. These storms originate over tropical waters, close to the equator. If the atmosphere is calm and the water is warmer than about 27℃, evaporation forces large amounts of moisture into the air, creating a low-pressure system. When this water vapor condenses, it releases heat that powers the circular winds that characterize these storms. Rainfall in the developing storm releases more heat, triggering a convection process that pulls more moisture-laden air up through the centre of the system. The storm grows via this feedback mechanism. The strongest winds are found immediately outside the centre, or 'eye', of the hurricane at ground level. Every one of these systems begins as a tropical depression—a system of thunderstorms with an overall circular motion and maximum sustained winds less than 62 km/h. When a storm becomes severe enough and the winds pick up to more than 62 km/h, it is designated a tropical storm. When the winds reach 119 km/h, the system is called a hurricane, typhoon or cyclone. An average of 10 tropical storms develop over the Atlantic Ocean each year, of which about six become severe enough to be called hurricanes. Besides strong winds and heavy rain, these hurricanes also create a 'storm surge', a massive wave beneath the centre of the storm. In the eye of the hurricane, air is sucked upward faster than it can rush in at the bottom. This lowers the atmospheric pressure under the eye of the storm; as a result, the eye tries to pull at the ocean itself, creating a bulge of water as much as six metres high that moves together with the storm. When is the hurricane season? Hurricane season officially runs from June I to November 30, but the most intense storms mainly occur between mid-August and mid-October. How are hurricanes classified? Tropical storms that get strong enough to be classified as hurricanes are categorized by the intensity of their wind speeds using the Saffir-Simpson scale. Only three Category 5 hurricanes have made landfall in the U.S. in the past century—one that struck the Florida Keys in 1935, Hurricane Camille in 1969, and Hurricane Andrew in 1992. How are tropical storms named? A tropical storm is given a name if its winds reach a speed of 62 kilometres per hour. An international committee has drawn up a list of 126 names—half male and half female—which are repeated after a six-year cycle. However, if a hurricane causes extensive damage, its name is retired from use. So far, more than 50 names have been retired, from Hazel in 1954 to Juan in 2003. Memorable hurricanes In August and September 1992, Hurricane Andrew wrought havoc across the Caribbean and Florida. Andrew was an unusual storm—after brewing for several days at low latitudes, it weakened and nearly vanished about 600 km east of Puerto Rico. But the storm regained its strength and moved northward with devastating results. Andrew left 17,000 people homeless in Florida alone and destroyed or badly damaged 85,000 homes. The storm caused a record $26.5 billion in property damage. In 2002 Andrew, initially classified a Force 4, was upgraded to have actually been a Force 5 storm. In November 1998, Hurricane Mitch tore through Central America, killing as many as 10, 000 people and leaving two million homeless in Nicaragua and Honduras. The storm's 300 km/h winds and heavy rains caused more than $3 billion in damage—more than half the combined gross domestic product of those two countries. Mitch also unleashed deadly landslides, and caused the worst flooding in the region in 200 years. In the storm's wake, with roads and infrastructure