Hurricane Sandy is expected to hit the eastern United States with freakish power as it meets a cold front during a rare convergence of weather factors that is expected to steer the storm inland and widen the reach of its lashing winds.
Here is a look at some of the reasons why the event dubbed "Frankenstorm" by some weather watchers is so unusual and why it could be one of the most destructive U.S. storms in decades.
* Hurricane Sandy will join with a cold front in an event similar to Hurricane Hazel in 1954, said Bruce Sullivan, a meteorologist with the National Oceanic and Atmospheric Administration's Hydrometeorological Prediction Center. "We don't have a lot to compare it to in the last 50 years or so," he said.
* One factor that sets Hurricane Sandy apart from last year's Hurricane Irene, which caused $4.3 billion in damage, is that it will produce more than a foot of snow in higher elevations, especially in West Virginia, said Eric Leister, meteorologist with AccuWeather.com. That could lead to widespread power outages.
* Hurricane Sandy also presents more potential for flooding than Irene because it will produce more storm surges, particularly along northern New Jersey, New York City and Long Island, said meteorologist Dan Petersen with the Hydrometeorological Prediction Center.
* Meteorologists are reluctant to predict how destructive Sandy could be overall compared to past storms including Irene, but say it has the potential to be catastrophic. "This is a historic event, and if it turns out as bad as it could be, it's going to be likely one of those storms that people will be talking about 30, 40, 50 years from now," Leister said.
* Most tropical storms that make landfall in the mid-Atlantic region move northeast and out toward the ocean. Sandy will move northwest and unleash its fury over a greater area of land than the average storm, Sullivan said.
* Sandy will be led inland on its destructive path by a high-pressure system over eastern Canada and a storm system moving southeast across the Tennessee Valley, Sullivan said. Those two systems and their winds will act like a "steering mechanism" and draw Sandy to the northwest, he said.
* This is late in the season for a hurricane to hit the northeastern United States, which could make Hurricane Sandy unusually destructive by allowing it to combine with colder air masses that are not normally present in the warmer summer months, Leister said.
VAST WIND FIELD
* Hurricane Sandy will generate heavy winds covering an area more than 500 miles in diameter, Sullivan said. By comparison, the hugely destructive Hurricane Andrew in 1992 unleashed heavy winds over an area about one-fifth that size, he said.
* The large wind storms generated by Hurricane Sandy will create major flooding and storm surges, said Chris Landsea, hurricane forecaster at the National Hurricane Center. Coastal areas will be inundated with up to 8 feet of storm surges, which will be devastating for low-lying areas, he said.
(Additional reporting by David Adams; Editing by Colleen Jenkins and Will Dunham)