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The actual 'Perfect Storm': A perfectly dreadful combination of nature's forces
(CNN) -- In the best-selling book "The Perfect Storm," and in the new movie with the same title, the most dramatic character is the weather.
The storm was officially known as "the Halloween nor'easter of 1991." The meteorologists who tracked it the last days of October that year did not call it "the perfect storm."
But forecasters did call it a perfect example of the deadly force of nature. Winds blasted over the ocean at more than 100 mph. Ocean waves peaked at 100 feet, the height of 10-story buildings. Waves 30 feet high battered the New England coast, destroying 200 homes. Nine people died, including the six-man crew of a swordfish boat from Gloucester, Massachusetts.
"This was truly an awesome example of nature taking advantage of everything she's got available," said David Vallee, a National Weather Service forecaster who tracked the storm in 1991.
'Three pieces of energy'
The storm did not arrive full blown. It built over a week, between October 26 and October 31. Three weather systems -- "three pieces of energy," Vallee called them -- came together, with deadly results.
The first was what Vallee called "a little, innocuous" low-pressure system that formed over the Great Lakes, then followed the usual path of North American weather: west to east, from Chicago to Maine, and on past Nova Scotia.
En route, it met the second piece of energy: An icy cold high-pressure system drafting down from Canada. The two systems combined into a storm in the North Atlantic, off Nova Scotia's coast.
The third piece of energy was what made the "perfect" storm so perfectly terrible: a late-season hurricane, Grace, blowing from the south.
By itself, a hurricane has colossal force. "A mature hurricane is by far the most powerful event on Earth," wrote Sebastian Junger in his book "The Perfect Storm." "The combined nuclear arsenals of the United States and the former Soviet Union don't contain enough energy to keep a hurricane going for one day."
In October 1991 the power of a hurricane joined forces with another storm.
It was a colossal collision of two seasons: winter and summer. "Arctic energy from Canada was driving steadily southward, while this ball of tropical energy from the hurricane was moving northward," said Vallee. "When they met, it caused this storm to explode, in weather terms."
Vallee remembered the satellite images of the "exploded" storm: a huge white whirlpool 2,000 miles wide that reached from Jamaica to the coast of Labrador. "It had almost a mystical beauty," he said.
But it was lethally dangerous, especially to anyone out on the North Atlantic.
In his book Junger wrote of the fate of one boat caught in the storm southeast of Nova Scotia: the Andrea Gail, a 72-foot steel-hulled swordfish boat.
On the evening of October 28, the Andrea Gail managed radio contact with fellow fishing boats farther from the storm. Through a scream of wind and static, the captain gave a terse report: They were doing their best to get through a storm so strong that it was ripping away equipment attached to the deck with steel bolts.
The Andrea Gail gave her position and signed off. No one reported hearing from her again. Days later, rescue and search teams found a few of the boat's fuel drums, but no trace of its six crew members.
The best guess is that the Andrea Gail went under within hours of last radio contact. It was most likely swamped by a wave. Although no one on board the Andrea Gail survived to tell what size the waves were, meteorologists say they know. Wind measurements show that waves in the area that night were towering, and terrifying.
Waves are generated by wind. The harder and longer the wind blows, and the larger the area over which it blows, the bigger the waves it will generate.
"Sixty mile-an-hour winds, over five hours, will raise seas from dead calm to about 19 feet," said Walt Drag, the National Weather Service's principal forecaster for the storm.
In October 1991, winds of that speed blew from morning until night over hundreds of miles of ocean. "Near the last known position of the Andrea Gail, the winds were blowing 60 miles an hour for almost 24 straight hours," said Drag. "The peak wave height there was about 75 feet."
A 75-foot wave could easily have swamped the 72-foot ship, and done so in a matter of seconds. "Water is tremendously powerful," said Drag. "We know that a foot of water can lift a 1,500-pound vehicle. Two feet of water can float vehicles away.
"You stand on shore and try to stand up in 4- or 5-foot breakers, and you get a sense of how strong waves are near shore. Now you go and multiply that 15 or 20 times, and you realize you're dealing with something that is quite stupefying."
Then it doubled back
The Andrea Gail was not even in the worst of the storm. "It was still in the developmental stages," said Drag. "It was 36 hours later that the storm was at its most intense stage." Winds peaked at 100 mph. Data buoys recorded waves of at least 100 feet, among the highest ever measured anywhere in the world.
Waves that high are something of a mystery to scientists. They know waves have a maximum theoretical height of about 190 feet, but they do not know how many ever get close to such a height, or how such monumental waves behave. "We only have theories about the biggest waves, because it's hard to get observations to quantify the theory," said Vallee.
Meteorologists have satellite images from space and readings from data buoys, although most of the buoys are no more than 100 miles from the coastline, hundreds of miles from where mid-ocean storms rage.
"What is most helpful," said Drag, "is real-time human transmission of information" -- reports from ships at sea. The problem, said Vallee, is that "there aren't that many ships out there, and the ones that are out there are going in the opposite direction of storms like these."
"We like to get that information, but they have to save their own lives first," said Drag.
Saving lives is the first obligation of forecasters. Early on October 29 they unexpectedly had thousands of lives to worry about -- on shore. The giant storm had taken a deadly turn. Instead of moving off over the North Atlantic, away from the United States, it "retrograded," doubled back toward Cape Cod and the New England coast.
Retrogressions are highly unusual, especially for huge storms with great momentum. "It's rare to have a system of that magnitude back up," said Vallee. Over three days, the storm churned back from Newfoundland to just south of Nantucket, picking up strength and speed.
It smashed into the shore on the afternoon of October 31 with waves 30 and 40 feet high, record wave heights for the southern New England coast. The waves dissolved ocean-view homes and splintered seaside communities. One hundred homes were lost in one town alone, Situate, Massachusetts. Property damage totaled $500 million.
It can happen again
Some scientists said the formation of the storm, and its retrogression, made it a freak, a "hundred year storm." But meteorologists say a storm just as powerful can happen again.
Another set of 100-foot waves has since been recorded, during a fast-moving 1993 storm in the North Atlantic. "It happened twice in two years in the Scotian shelf," said Drag. "Why not again, and why not soon?"
Those who chart Atlantic weather say storms are getting stronger. Some blame the greenhouse effect. "Is there some hint that global warming is the reason?" said Vallee. "Maybe. Or is it sunspot cycles? Is it fluctuations in solar activity? We don't know enough to make an absolute answer."
What meteorologists can say with certainty is that future storms will be a greater threat to a greater number of people, because more people have built and settled in coastal areas and on floodplains. "We need to give great respect to the water and wind," said Drag. "And not have a cocksure attitude that we can handle anything."
Humans, even with the clearest satellite images, the best computer models, the most experienced forecasters, are no match for 100 mph winds, for waves the size of apartment buildings, for explosive storms that turn around, mid-fury, for a roundhouse attack.
"No matter how much we think we understand the processes of nature, nature can always do something a little different, a little unexpected," said Vallee. "It makes you realize how small we are."
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