A deadly recipe

Published 8:51 pm Tuesday, June 8, 2010

To create one of nature’s most deadly forces, it takes only two elements: water and air.

When the conditions are right, the two produce a hurricane.

“When you have the right ingredients in terms of water temperatures and the kind of wind flow in the atmosphere, it creates a huge power,” said National Weather meteorologist Anthony Siebers.

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The beginning of hurricane season is June 1, when waters traditionally begin to warm. The season ends Nov. 30. The peak time is from August to September, when waters are warmest, but hurricanes have been known to form outside the season’s official boundaries, as well.

When waters become at least 82 degrees to a depth of 160 feet, it is possible for hurricanes to begin to form.

The beginning stage of a hurricane is a tropical wave, which provides the focus for a developing hurricane or tropical storm. As many as 100 waves move into the Atlantic from the west coast of Africa during hurricane season.

A tropical depression will form as an organized system of clouds and thunderstorms with winds of up to 39 miles per hour. It has no eye and does not typically have the organization or the spiral shape of more powerful storms. When the thunderstorms increase, a cyclonic shape begins to form and winds are between 39 and 73 miles per hour, the storm is considered a tropical storm.

The storm is classified as a hurricane when winds reach 74 miles per hour and the storm develops an eye, a calm center. The eye can range from nearly nine miles to 50 miles in diameter and maximum winds have been recorded at 195 miles per hour.

“When a storm forms as a wave off the African coast, if the conditions are ripe, the wave can develop from a main storm to a tropical storm to a hurricane,” Siebers said.

The winds needed to foster a hurricane, however, must be light. Strong winds can cause a forming hurricane to dissipate. The better the wind conditions, the stronger the storm.

“There are five different levels of hurricanes, One being the weakest,” Siebers said. “Isabel only had Category One winds, but she tore down so many trees and caused so much damage, it’s scary to think about what a Category Three storm would look like if it reached the land.”

Of the three areas — the Gulf of Mexico, the African coast and the Atlantic — where hurricanes that impact the East Coast develop, the ones most dangerous to Virginia come from the Atlantic.

“Hurricanes can form in the Gulf, Atlantic or off the coast of Africa, where the classic hurricanes are,” Siebers said. “If you look at the coastal areas though, we’re normally worried about the ones that come from the Atlantic. If they’re coming from the Gulf, they have to travel across a lot of land, which slows them down.”

While the most dangerous hurricanes are those that intensify when they travel over land, Siebers said it rare for a hurricane to do so.

Normally, when a hurricane hits land, it loses its warm energy source — an essential component to a hurricane — and, combined with the friction from the land, the hurricane loses momentum.

“The warm water is the fuel that drives the energy in the storm,” Siebers said. “You need that water for its evaporation. That’s why they weaken and dissipate or stay in the ocean and re-curve to move to the north and never hit land.”