In contrast, the Atlantic Ocean averages about ten storms annually, of which six reach hurricane status. On average, 26 tropical cyclones form in this region each year, of which seventeen reach hurricane (typhoon) status. The most active area is the northwestern Pacific Ocean, which contains a wide expanse of warm ocean water. The number of hurricanes occurring each year varies widely from ocean to ocean, depending on how much warm ocean water exists. Where Do They Occur?īecause tropical cyclones are like giant engines that use warm, moist air as fuel, they form only over warm ocean waters near the equator. The increasing winds that spin around the center of the storm draw heat and moisture from the warm ocean surface, providing more fuel for the rising motions that produce the clouds. Like an ice skater whose body spins faster as his arms are drawn inward, air near the surface speeds up as it spirals in towards the center of the low-pressure area. What factors influence the strength or intensity of hurricanes? Higher pressure air from above flows down into the eye. It is very calm and clear in the eye, with very low air pressure. The whole system of clouds and wind spins and grows, fed by the ocean's heat and water evaporating from the surface.Īs the storm system rotates faster and faster, an eye forms in the center.

Forming clouds (condensation) releases heat, which helps the rising air rise further, rising all the way to the top of the troposphere (8.5 miles above the surface). As the warm, moist air rises, the water vapor in the air forms clouds. As the warm air continues to rise, the surrounding air swirls in to take its place.

Then that 'new' air becomes warm and moist and rises, too. Another way to say this is that the warm air rises, causing an area of lower air pressure below.Īir from surrounding areas with higher air pressure pushes into the low-pressure area. Because this air moves up and away from the surface, there is less air left near the surface. The warm, moist air over the ocean rises upward from near the surface. But they do know that two main ingredients are necessary: warm water and winds that don't change much in speed or direction as they go higher in the atmosphere. Scientists don't know exactly why or how a hurricane forms. How do they form? How do warm ocean waters fuel hurricanes? High vertical wind shear - winds that are changing significantly with height - tends to rip storms apart. Low vertical wind shear - winds that change very little going up through the atmosphere - is needed for hurricane development.

Usually, the surface water temperature must be 26 degrees Celsius (79 degrees Fahrenheit) or higher for a hurricane to form.The rate at which wind speed or direction changes with height is called vertical wind shear. Warm ocean waters provide the energy needed for a storm to become a hurricane. Whatever they are called, tropical cyclones all form the same way. The scientific term for these storms is “tropical cyclone.” Only tropical cyclones that form over the Atlantic Ocean or the eastern Pacific Ocean are called 'hurricanes”. These storms are also called by other names, such as typhoons or cyclones, depending on where they occur. They are said to be the most violent storms on Earth. That's quicker than a cheetah can run which is the fastest animal on land. Hurricanes are large, swirling storms with winds of 119 kilometers per hour (74 mph) or higher.

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