This story was originally published about the threat of storm surge posed by Hurricane Irma. It has been updated to reflect the East Coast "bomb cyclone."

(CNN) A powerful "bomb cyclone" is battering the East Coast with ferocious winds, rain and snow. But it's ocean waves that pose the greatest threat to 22 million people living in coastal communities. In fact, the National Weather Service in Boston is calling it a "LIFE & DEATH situation."

Much of the threat is due to storm surge, which CNN meteorologists have estimated could force 4 feet of water into coastal neighborhoods, damaging homes and flooding streets with frigid ocean water.

Storm surge is commonly associated with hurricanes. It was a huge threat to communities along the Gulf Coast last fall during Hurricanes Harvey and Irma , but it can be a treacherous element of any coastal storm.

Privately, you may be wondering (and you wouldn't be alone): "What is a storm surge?"

"A storm surge is a rise in water level caused by a strong storm's wind pushing water on-shore," said CNN meteorologist Brandon Miller. "The wind literally piles up the ocean water and pushes it on the land."

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