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.”

The National Weather Service says almost half of all deaths from tropical cyclones come from storm surge.

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 exactly is 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.”

Geography, tide-cycle and wind direction are all factors in how severe storm surge could be, Miller said. The stronger the storm, the stronger the winds and the higher the storm surge will be.

storm surge storm tide graphic

Storm surge also can exacerbate flooding. As the water piles up along the coast, rivers and streams that typically drain into the ocean can become clogged farther upstream, forcing water levels to rise.

Storm surge can also exacerbate inland flooding. As the water piles up along the coast, rivers and streams that typically drain into the ocean can become clogged further upstream, forcing water levels to rise.

That water doesn’t just leave. Depending on how much water was pushed ashore and the area’s watershed, it may hang around, causing further damage to communities.

Due to climate change, storm surge has become an even greater threat in recent years.

“Sea levels have risen in most places by about 1 foot over the past century. The higher baseline ocean level allows storm surges to reach even higher, increasing their destructive capabilities,” Miller said.

Regardless, storm surge is a dangerous and destructive component of any coastal storm, especially those as powerful as the “bomb cyclone” currently hammering the East Coast.

“The swelling ocean’s tide can overtop, damage or destroy coastal barriers such as dunes and sea walls,” Miller said. “The destructive floodwaters can reach hundreds of feet inland, damaging structures several streets away from the ocean-front.”

CNN’s Brandon Miller, Gene Norman and Judson Jones contributed to this report.