5 reasons why Sandy is expected to be a superstorm

A northbound hurricane •Hurricane Sandy is moving slowly toward the north-northeast but is expected to turn to the north and west later Sunday and Monday, forecasters say. At some point, it's expected to become what's known as an extratropical storm. Unlike a tropical system like a hurricane, which gets its power from warm ocean waters, extratropical systems are driven by temperature contrasts in the atmosphere.

Although Sandy is currently a hurricane, it's important not to focus too much on its official category or its precise path (current models show it making landfall over New Jersey or Delaware sometime early Tuesday). It's a massive system that will affect a huge swath of the eastern U.S., regardless of exactly where it hits or its precise wind speed. For example, tropical storm-force winds can be felt more than 500 miles from the storm's center, according to the National Hurricane Center. It's already caused some minor flooding in North Carolina's Outer Banks and has prompted evacuations elsewhere. The Federal Emergency Management Agency has personnel and supplies spread as far west as the Ohio River Valley, said Craig Fugate, the agency's director.

Early winters storm •Sandy is expected to merge with a wintry system from the west, at which point it will become the powerful superstorm that has forecasters and officials across the eastern U.S. Winds from that system will pull Sandy back toward the U.S. mainland.

Arctic air from the north • Frigid air coming south from Canada also is expected to collide with Sandy and the wintry storm from the west, creating a megastorm that is expected to park over the northeast for days. The brunt of the storm could hit areas farther inland. Officials are bracing for the worst: nearly a foot of rain, high winds and up to 2 feet of snow.

High tides could worsen flooding • Further complicating matters is the possibility for dangerous storm surges: A full moon means the tides will be higher than usual, which will make it easier for the storm's powerful winds to push water into low-lying areas. That, coupled with the threat of several inches of rain, has officials working to shore up flood defenses.

Storm surge could reach anywhere from 2 to 11 feet along the northeastern coast, forecasters say. Inland river flooding also is a serious concern.

Combo of snow, wind increases risk for widespread power outages • Storms in recent years have left hundreds of thousands of people in the eastern U.S. without power, sometimes for days at a time. Utilities have been bringing in extra crews and lining up tree trimmers so they're prepared, and with good reason. The superstorm brings two possibilities for knocking out electricity. For one, hurricane-force winds of at 74 mph could send tree branches into power lines, or even topple entire trees and power poles. Those left standing could succumb to snow, which could weigh down still-leafy branches enough to also topple trees.