Hurricane formation
HOW IS A HURRICANE FORMED?
Click the picture for an explanation
of hurricane formation. (avi 5.7Mb)
Hurricanes usually originate as a cluster of showers and thunderstorms in tropical waters. The process by which a disturbance forms and subsequently strengthens into a hurricane depends on many conditions. However, there are three major factors which must be met before hurricane formation. Those factors include warm water and moisture, favorable low level winds, and light upper level winds.
A hurricane's main source of energy comes from heat. Developing hurricanes gather heat and energy through contact with warm ocean waters. Most of the time in the hurricane generation season ocean water temperatures are warmer than 79 degrees.
Winds near the ocean surface need to rotate counter-clockwise (low pressure) in order for a cluster of storms to develop into a tropical system. This counter-clockwise flow directs winds and moisture inward to a central point. Once this moisture nears the central point, the center of a low pressure system, it is lifted into the atmosphere to form more showers and thunderstorms.
As this process repeats itself, the more energy and moisture is available; and the area of showers and thunderstorms grows and intensifies, leading to the formation of a tropical system.
The upper portion of the atmosphere is to a hurricane what a muffler is to a car. All of the exhaust from a car must go somewhere so it goes through a hollow tube (muffler) into the open air. If an object is placed in the muffler or it is clogged, the car will not run properly. The same situation can be applied to tropical systems. All the upward moving moisture and water vapor (exhaust) in the center of the low must go somewhere. Upper levels of the atmosphere act as the tropical system's "muffler". In an ideal situation, light upper level winds will allow this moisture to be "fanned out" to other parts of the storm. If there are strong winds aloft, they act as a lid to the "muffler," and the moisture has no place to go. Hence, the storm has no means to intensify and may even collapse if the upper level winds are strong enough.
What are the different parts of the hurricane?
The typical hurricane has 2 or 3 and sometimes more outer convective bands. These bands are comprised of cells resembling ordinary thunderstorms and can be up to 300 miles from the eye. The outer convective bands are generally 40 to 80 miles apart and come in advance of the main rain shield.
The rain shield is a solid or nearly solid area of rain that typically becomes heavier as one approaches the eye. The outer edge is well defined and its distance from the eye varies greatly from storm to storm. The wind, both sustained and peak gusts, keeps increasing as one moves through the rain shield toward the storm's eye.
Spiral convective rings or bands are the regions of active showers and thunderstorms than encircle the centers of tropical cyclones. They are prevalent in more intense hurricanes and curve cyclonically inwards toward the center of the storm where they appear to merge and form the wall of the eye.
The eye wall is an organized band of thunderstorms that immediately surrounds the center or eye of a hurricane. It's generally around 15 miles wide and typically contains the fiercest winds and most intense rainfall.
The eye is a relatively calm center of the hurricane. The winds are light, and skies are partly cloudy or even clear. The average hurricane eye diameter is a little over 20 miles. In general, when the eye is shrinking in size, the hurricane is intensifying. During the daytime, the passage of the hurricane's eye over a community is usually accompanied by sunny skies and a rise in temperature. After the eye's passage, the violent wind howls in the opposite direction to what it was right before the eye moved over and the heavy sheets of rain return.
IMAGE SOURCE: NWS / Insight Magizine / Melody Warford
printer friendly