NewsOctober 25, 2012

Hurricane Sandy Aims For East Coast As a 'Frankenstorm'

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Andrew Freedman

By Andrew Freedman

As Category 2 Hurricane Sandy continues to lash the Bahamas with strong winds, heavy rain, and a damaging storm surge, computer models were projecting even more dire scenarios for locations along the East Coast of the U.S. from Virginia north to Maine, with an intense, perhaps even historic, storm making landfall there early next week. Most projections from Thursday were indicating that Sandy will slam much of the northeastern corridor, home to about 50 million people, not to mention billions in expensive real estate and infrastructure.

Because the storm may have hybrid characteristics of both a hurricane and a nor’easter — not to mention that it could hit on Halloween — the National Weather Service has dubbed the system “Frankenstorm.”

A zoomed in view of Hurricane Sandy as it was rapidly intensifying on Wednesday. 
Click to enlarge the image.
Credit: NOAA Environmental Visualization Laboratory.

The storm will have a wide array of dangers associated with it, including record inland and coastal flooding, widespread damaging winds that could gust above hurricane force, and high_elevation snows. The Capital Weather Gang blog has a breakdown of what different tracks would mean for the nation's capital, illustrating the potential for disaster. The National Hurricane Center has already noted an expansion in the storm's wind field, and this trend is expected to continue for the next few days.

Depending on the exact track of the storm, it could even have impacts as far west as Ohio and western Pennsylvania, which may receive wet snow in higher elevations. And with the presidential election as a backdrop, there could be widespread power outages, including in political swing states such as Ohio, New Hampshire, Virginia, which could influence voting patterns on Nov. 6, Election Day.

While confidence has increased that the storm will impact the East Coast, there remains considerable uncertainty about where Sandy will come ashore, or even if it will make landfall or just near the coast. The track and structure of the storm will help determine the impacts in places from Norfolk, Va., to Portland, Maine.

Mayor Michael Bloomberg of New York City and officials in several other states are already taking actions to prepare for the storm. New York is especially vulnerable to coastal flooding, and with astronomical high tides taking place at the same time as this storm, there is a significant potential for massive coastal flooding (again though, this depends on the exact storm track and intensity). Tropical Storm Irene, which passed over Manhattan in September 2011, came close to flooding part of the New York subway system, and this Frankenstorm has the potential to create an even larger storm surge.

As hurricane Sandy moves northward, it is going to interact with powerful jet stream winds that are associated with a surge of cold Canadian air, at the same time that it draws heat from an unusually warm Gulf Stream current. That will allow Sandy to morph into a large-scale hybrid storm, one that is part hurricane, part nor’easter.

A computer model simulation from the European model, showing the “Frankenstorm”

A strong ridge of high pressure over the Canadian Maritimes and Greenland will help push the storm northwestward, into the Mid-Atlantic or New England, rather than allowing it to move out to sea. That will also make the storm a slow mover, which will only worsen the damage in affected areas. A ridge of such high pressure is known as a “blocking high,” and while its occurrence is not particularly unusual, its intensity is.

Recent studies have shown that blocking patterns have appeared with greater frequency and intensity in recent years. Some scientists think that may be related to the loss of Arctic sea ice, which is one of the most visible consequences of manmade global warming. The 2012 sea ice melt season, which ended just one month ago, was extreme, with sea ice extent, volume, and other measures all hitting record lows. The loss of sea ice opens large expanses of open water, which then absorbs more of the incoming solar radiation and adds heat and moisture to the atmosphere, thereby helping to alter weather patterns. Exactly how weather patterns are changing as a result, however, is a subject of active research.

While it is not unusual to have a high pressure area near Greenland, its intensity is striking for this time of year. As Jason Samenow of the Capital Weather Gang wrote on Wednesday, the North Atlantic Oscillation, which helps measure this blocking flow, “is forecast to be three standard deviations from the average — meaning this is an exceptional situation.”

On Thursday, Will Komaromi, a graduate student in meteorology at the University of Miami in Florida, wrote about the large-scale weather pattern that he says could make this storm event even more intense than the benchmark storms of the past, such as the so-called Perfect Storm in 1991, which occurred at the same time of year:

“Normally a hurricane weakens as it moves northward, as it encounters an increasingly unfavorable environment. This means greater wind shear, drier air, and lower sea surface temperatures. However, with phasing events, the tropical system merges with the mid-latitude system in such a way that baroclinic instability (arising from sharp air temperature/density gradients) and extremely divergent air at the upper-levels more than compensates for a decreasingly favorable environment for tropical systems,” he wrote.

Stay tuned to Climate Central for continuing coverage of this storm.

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