how do hurricanes form?
Hurricanes form over the warm tropical waters because the warm ocean water is the fuel for the storm. In fact, the water must be about 81 degrees F for hurricanes to thrive(1). There is a band across the globe near the equator called the Intertropical Convergence Zone or ITCZ, and this is the general area where hurricanes live. (Hurricane Fran) It all starts as a complex of thunderstorms which then begins to organize together. Once it starts to circulate around a central area of low pressure it may become a tropical depression (sustained winds of 23-39 MPH). Then as it gains strength it may become a tropical storm (sustained winds of 39-74 MPH). Once it reaches 74 MPH it will be a hurricane. Most hurricanes that threaten the US are from the Atlantic Basin. Atlantic hurricanes originate anywhere from the Caribbean or even off the African coast. The reason for this is that the trade winds are the dominate winds in this region, and they blow from Africa to the Gulf of Mexico.
Hurricanes are mind-boggling in their size and strength. Modern technology lets us see how big hurricanes are and track them through satellite imagery, while storm-penetrating aircraft measure their strength, in terms of wind speeds and atmospheric pressure. That technology gives us detailed warnings that people a century ago never had. Hurricanes usually form in the tropical zones north and south of the equator, where warm waters offer ample fuel for storm formation. That’s where you see convection, where warm air rises and forms clusters of thunderstorms. The Coriolis effect, created by the Earth’s spinning motion, may cause this cluster of storms to rotate (counter-clockwise above the equator, or clockwise below), but the system has to be a few hundred miles from the equator for the Coriolis force to exert an effect. If the system becomes organized and strong enough, with sustained winds of 39 miles per hour, it becomes a tropical storm.
Hurricanes only form over really warm ocean water of 80°F or warmer. The atmosphere (the air) must cool off very quickly the higher you go. Also, the wind must be blowing in the same direction and at the same speed to force air upward from the ocean surface. Winds flow outward above the storm allowing the air below to rise. Hurricanes typically form between 5 to 15 degrees latitude north and south of the equator. The Coriolis Force is needed to create the spin in the hurricane and it becomes too weak near the equator, so hurricanes can never form there. (Graphic Credit: UCAR) Click Here to learn more about hurricanes from UCAR. What is storm surge? Storm surges are frequently the most devastating element of a hurricane. As a hurricane s winds spiral around and around the storm, they push water into a mound at the storm s center. This mound of water becomes dangerous when the storm reaches land because it causes flooding along the coast. The water piles up, unable to escape anywhere but
Hurricanes are the most awesome, violent storms on Earth. People call these storms by other names, such as typhoons or cyclones, depending on where they occur. The scientific term for all these storms is tropical cyclone. Only tropical cyclones that form over the Atlantic Ocean or eastern Pacific Ocean are called “hurricanes.” Whatever they are called, tropical cyclones all form the same way.
