henri wind forecast sunday morning
Henri nearly a hurricane, warnings posted for New England.
03:31 - Source: CNN

Editor’s Note: This story has previously been published related to other hurricanes’ threat of storm surge. It has been updated to reflect conditions with Henri.

CNN  — 

When Henri makes landfall – probably on New York’s Long Island or southern New England – the major storm will bring with it flash flooding, extreme winds and storm surge, the National Hurricane Center said Friday.

Almost half of all deaths from tropical cyclones come from storm surge.

While many people focus on the wind speed of storms, the danger often comes from the water flowing in from the ocean.

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.”

All that water has nowhere to go

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.

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.

The National Weather Service in a 2014 report said that most surge deaths occurred in Hurricane Katrina and several other big, powerful storms. In a majority of storms, excessive rainfall that leads to drownings is the leading cause of death.

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