Hurricanes pose risk to offshore wind farms

When an oncoming hurricane curves offshore — as most do — we usually breathe a sigh of relief. But soon, those offshore storms might give us something more to worry about.

By Heribert Proeppe, AP file

Windmills in the North Sea, off of the village of Blavandshuk near Esbjerg, Denmark.

By Heribert Proeppe, AP file

Windmills in the North Sea, off of the village of Blavandshuk near Esbjerg, Denmark.

Offshore hurricanes could demolish half the turbines in proposed wind farms just off the USA's coastlines, according to a study out Monday in the Proceedings of the National Academy of Sciences.

"We find that hurricanes pose a significant risk to wind turbines off the U.S. Gulf and East coasts, even if they are designed to the most stringent current standard," the authors from Carnegie Mellon University in Pittsburgh write.

Engineer Stephen Rose and colleagues conducted the study in response to a 2008 report from the U.S. Department of Energy, which said that wind energy should ideally provide one-fifth of all electricity in the USA by 2030. The engineers estimated that over a 20-year span many turbine towers would buckle in wind farms enduring hurricane-force winds off the coasts of four states — Massachusetts, New Jersey, North Carolina and Texas — where offshore wind-farm projects are now under consideration.

Despite their record of death and destruction in the USA, 75% of all Atlantic basin hurricanes remain offshore and do not hit land, according to Chris Landsea, science and operations officer at the National Hurricane Center in Miami.

Wind turbines are vulnerable to hurricanes because the maximum wind speeds in those storms can exceed the current design limits of wind turbines, according to the study.

Failures can include loss of blades and buckling of the supporting tower.

The research incorporated the current construction standards for the turbines, reports Rose. "Our study assumed wind turbine design for the current standards, with a maximum sustained wind speed of 111 mph near the top of the turbine, about 90 meters (about 300 feet) above the surface. This is the equivalent of a Category 3 hurricane," he says.

The study had to use computer models to simulate hurricanes' effect on the wind turbines, as no offshore wind turbines have yet been built in the USA (although there are 20 offshore wind projects in various stages of planning).

However, turbine tower buckling has occurred in typhoons in the Pacific. Hurricanes are the same type of storms as typhoons.

Of the four locations examined in the study, offshore of Galveston County, Texas, is the riskiest location to build a wind farm, followed by the Outer Banks of North Carolina, Atlantic City and Martha's Vineyard, Mass.

"Galveston was the riskiest because it gets hit by hurricanes the most frequently," says Rose.

The damage caused by Category 3, 4 and 5 hurricanes is important for offshore wind development in the USA, the study notes, because every state on the Gulf of Mexico coast and nine of the 14 states on the Atlantic Coast have been struck by a Category 3 or higher hurricane from 1856 through 2008.

"As you get to Categories 3, 4, 5 — that's where the risks are," says Rose. "The intense hurricanes pose the most risk."

However, damage could be greatly reduced by building the farms in lower-risk areas and boosting the abilities of turbines to withstand higher winds.

This would "greatly enhance the probability that offshore wind can help to meet the United States' electricity needs," according to the study.

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Dust Obscures Picture of Hurricanes in Warming World (LiveScience.com)

As a doozy of a hurricane season wraps up, scientists are eager to understand how these storms will change as the climate warms. They are finding several curious influences that can cause hurricanes to move in counterintuitive ways.

Scientists have a pretty good idea that hurricanes will become less frequent and more intense due to climate change, said oceanographer Chunzai Wang during a recent visit to the National Oceanic and Atmospheric Administration's Atlantic Oceanographic and Meteorological Laboratory (AOML) in Miami, where scientists study everything from ocean acoustics to hurricane forecasting.

But other curveballs that recently have come to light complicate the picture. One is dust.

Every year, storms over West Africa disturb millions of tons of dust, and strong winds carry those particles westward into the skies over the Atlantic Ocean, where many hurricanes form. [Infographic: Storm Season! How, When & Where Hurricanes Form]

During a dust spike triggered by heavy rainfall, there's a drop in hurricanes in the Atlantic basin, Wang said. As the dust spreads into the atmosphere, it increases what's called the vertical wind shear, the change in wind direction that comes with height, Wang said. That's bad news for hurricanes, because too much wind shear can break up tropical cyclones (the general term for hurricanes and tropical storms).

A few years ago, scientists at the University of Wisconsin, Madison, pored over satellite data from the past 25 years and found that during years when the dust storms rose up, fewer hurricanes swept across the Atlantic. Periods of low duststorm activity were followed by more-intense hurricane activity.

Another curveball is warm water. Earlier this year, Wang and colleagues also published a report finding that, counterintuitively, a large pool of warm ocean water in the Atlantic Ocean keeps hurricanes away from the United States.

Wang said a hurricane behaves like a leaf floating in a river, totally at the whim of the current. So goes the river, so goes the leaf. A large Atlantic warm pool causes the atmospheric "river" to steer toward the northeast, carrying a hurricane with it and away from the United States.

This scenario played out during the 2010 hurricane season, when a large warm pool kept an otherwise active hurricane season from having an impact on the United States.

This story was provided by OurAmazingPlanet, a sister site to LiveScience. You can follow OurAmazingPlanet staff writer Brett Israel on Twitter: @btisrael. Follow OurAmazingPlanet for the latest in Earth science and exploration news on Twitter @OAPlanet and on Facebook.

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History of Hurricanes in New York City (ContributorNetwork)

New York City is getting ready for a monster storm. The entire network of its famed subway system will be shut down in anticipation of Hurricane Irene. Parts of the city will be evacuated in low-lying areas to ensure elderly residents will be safe in case flooding occurs.

In terms of hurricane preparedness, New York City isn't exactly on the cutting edge. However, because it is the largest city in the United States there must be precautions taken to guard its most vulnerable citizens. Perhaps the lessons learned from past New York City hurricane strikes have served as a lesson to current leaders.

1821 Hurricane

Hurricanes didn't get names until 1950. Back in early September 1821, a gigantic storm bore down on New York so fast it caught residents of the city unaware. Walls of water 13 feet high brought high water south of Canal Street. New York Magazine reported the only thing that saved the city from complete ruin was that the brunt of the storm surge came in at low tide.

There were an unspecified number of deaths as records in 1821 were scarce. However, the areas decimated by the 1821 Hurricane were far less populated than they are today so the loss of life was kept relatively low by today's standards.

Hog Island Destroyed, 1893

An estimated Category 2 hurricane hit the area in 1893. The storm completely washed away Hog's Island, a resort part of New York City Aug. 22, 1893. No one in the modern age of New York had seen anything like it. Hog's Island was a mile long. A 30-foot storm surge of water completely washed it away literally overnight.

The site where the hurricane made a direct hit is where JFK International Airport now sits. Should Hurricane Irene pack the same punch as the storm in 1893, imagine what might happen. Howling winds and heavy rain may not do well in low-lying areas of New York.

Long Island Express, 1938

The hurricane dubbed the Long Island Express hit eastern Long Island as a Category 3 hurricane on the afternoon of Sept. 21, 1938. It spared New York City for the most part as the strongest 180 mph winds stayed in sparsely populated areas of Long Island. The storm killed 10 people in New York City alone and 200 overall. Had the hurricane moved 75 miles farther west, New York City would have taken a direct hit.

Insurance adjusters are fearful of another hit like the Long Island Express. Now, a storm of that magnitude would cause damage over $10 billion. Other modern hurricanes have dumped lots of rain and wind on New York. Hurricane Belle grazed New York in August of 1976 causing heavy rain. Hurricane Gloria also pelted the region with monsoon rains in late September of 1985.

As Hurricane Irene approaches, New York is doing what many residents in hurricane-prone areas do. They are hoping for the best and preparing for the worst.

William Browning is a research librarian.

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The Formation and Behavior of Hurricanes (ContributorNetwork)

Hurricanes, in part because of the large area they cover, are one of the most dangerous and damaging of all natural disasters. According to National Center for Atmospheric Research numbers, each year hundreds hurricanes cause an average of more than $5 billion in property damage and more than 20 deaths in the United States alone, arguably one of the best prepared countries in the world. If not for the advance warnings provided by modern forecasting techniques, the death tolls would be dramatically higher.

While our understanding of hurricanes is far from perfect, scientists do understand many of the factors that cause hurricanes to form, strengthen and ultimately collapse as they run out of energy.

What defines a hurricane?

A hurricane is a tropical storm with winds of 74 mph or more, according to Louisiana Homeland Security and Emergency Preparedness. The winds circulate around the storm's center or eye, traveling counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. Hurricanes can include dangerous winds, extremely heavy rains, storm surges, and may even spawn tornadoes.

What conditions are necessary for the formation and growth of a hurricane?

Hurricanes draw their energy from the warm waters of the tropical oceans, requiring surface water temperatures of 81 degrees or higher, says the University of Illinois. They form over oceans because moisture in the air is also required. Moist air holds more energy in the form of latent heat. Tropical winds also play a role. Low wind shear allows the storms to build vertically, concentrating the energy of latent heat from the atmosphere over a smaller area, increasing the intensity of the storm and likelihood of it developing into a hurricane. Hurricanes form in the tropics along either side of the equator but not right on it, because they also require help from the Earth's coriolis force to produce their initial spin or rotation.

What is the difference between a hurricane, a typhoon and a tropical cyclone?

These three terms all refer to the same type of storm. The only real difference is the location, says the University of North Carolina. In North America, we use the term hurricane, but the same kinds of storms are called typhoons in the Northern West Pacific Ocean and tropical cyclones in the Indian Ocean and Southern West Pacific Ocean. Tropical cyclone is also a generic term for tropical depressions with circulating winds whether or not they reach hurricane strength.

What are the growth stages of a hurricane?

The conditions required for a hurricane may start out as a series of thunderstorms called a tropical depression that have a central region of low pressure and begin to develop some cohesive rotation. As the associated winds increase in speed to 39 mph to 74 mph, the rotation of the storm becomes more organized and more circular. At this point, it will be called a tropical storm and receive an official name. As a tropical storm strengthens further a distinctive eye forms in the center of the swirling winds. Minimum sustained wind speeds of 74 miles per hour or greater make the storm a hurricane.

How does a hurricane get stronger?

Hurricanes are a self-reinforcing system. They are fueled by warm, moist air flowing toward a central region of low pressure. The incoming air is pushed vertically near the storm's center. As it rises, the air cools and can no longer hold as much moisture. The moisture in the air condenses out in the form of precipitation. As it does so, heat held by the water vapor is released into the surrounding air. As the air is heated, it expands, pushing air away from the storm center at the upper level. This reduces the amount of air above the center of the storm (measuring in the mass or weight of the air), which lowers the air pressure at the lower levels of the hurricane's center. Reduced air pressure here draws even more air toward the center at the lower level and the hurricane's strengthening cycle repeats continuously as long as the air being drawn into the system has enough "latent heat" trapped in water vapor to keep the cycle going.

Why do hurricanes seem to aim for the east coast of the United States?

Hurricanes that form along the east or west sides of North America are generally pushed in a northeasterly direction due to the prevailing direction of the tropical trade winds in that location. As they move up the east coast, they get pushed along by the Gulf Stream which tends to push them back out over the North Atlantic.

Why do hurricanes weaken or dissipate after they make landfall?

Hurricanes require a constant influx of warm, very moist air to sustain themselves. As they move north into cooler waters or the eye moves over land, there simply isn't enough moisture or latent heat to allow the hurricane to strengthen. As its latent heat is released, it runs out of energy and the system weakens.

Do hurricanes cause tornadoes?

Yes. The strong winds circling in the hurricane's eye wall can produce very intense tornadoes either within the eye wall itself or just outside it. Hurricane-spawned tornadoes can occur with little warning and can be very dangerous even in areas that are not accustomed to tornado activity.

What is a storm surge?

A storm surge occurs when the winds of a hurricane are blowing toward the shoreline from the ocean. They literally push the surface water toward they land where it piles up, getting deeper and deeper as long as the winds continue in the same direction. The storm surge can be compounded by incoming tides resulting in flooding far inland.

Brad Sylvester spent more than 18 years working in the consumer electronics industry before becoming a full-time freelance writer. He has a keen interest in science and the environment, and possesses a nearly insatiable curiosity about almost everything. You can follow him on Twitter @back2n8ure.

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