abc CH11: Steve Stewart
As Hurricane Florence moves closer to the coast, we've been hearing a lot about 'storm surge.'
Large death tolls have resulted from the rise of the ocean associated with many of the major hurricanes that have made landfall. Hurricane Katrina is a prime example of the damage and devastation that can be caused by surge. At least 1,500 people lost their lives during Katrina and many of those deaths occurred as a result of storm surge.
Storm surge is produced by water being pushed toward the shore by the force of the winds moving counter-clockwise around the storm. The maximum potential storm surge for a particular location depends on a number of different factors. Storm surge is a very complex phenomenon because it is sensitive to the slightest changes in storm intensity, forward speed, size, angle of approach to the coast, central pressure and the shape and characteristics of the coastline.
In addition to the power of surge, battering waves on top of the surge can cause significant destruction to structures. Water weighs around 1,700 pounds per cubic yard; extended pounding by waves can demolish any structure not specifically designed to withstand such forces. The two elements work together to increase the impact on land because the surge makes it possible for waves to extend inland.
(CNN)Hurricane Florence's wrath begins today.
The Carolina coasts can expect winds topping 80 mph late Thursday afternoon. And that's just the prelude to untold days of misery.
Don't be fooled by the fact that Florence has weakened slightly to a Category 2 hurricane; categories only denote the speed of sustained winds.
What makes this hurricane extremely dangerous are the deadly storm surges, mammoth coastal flooding and historic rainfall expected far inland.
"I don't care if this goes down to a Category 1," CNN meteorologist Chad Myers said. "We're still going to have a Category 4 storm surge."
TRACK THE STORM
Even worse: Florence is expected to hover over the Carolinas, whipping hurricane-force winds and dumping relentless rain at least through Saturday.
By the time it leaves, it's expected to have unloaded 10 trillion gallons of rainfall in North Carolina, weather.us meteorologist Ryan Maue said. That's enough to fill more than 15 million Olympic-size swimming pools.
• Fierce winds and rain have started: "Rain bands with tropical-storm-force winds (are) moving onshore on the outer banks of North Carolina," the National Hurricane Center said. Tropical-storm-force winds are between 39 and 73 mph.
• Florence is getting closer: As of 8 ET Thursday morning, the center of Florence was about 170 miles east-southeast of Wilmington, North Carolina, and about 220 miles east of Myrtle Beach, South Carolina.
• The path of the storm: Florence's center will approach the North and South Carolina coasts late Thursday and Friday, but it's unclear exactly when and where and it will make landfall. As the storm moves inland, Georgia, Virginia and Maryland will also be in peril.
• Storm surge is a huge threat: Strong winds will send rising water inland from the coastline of the Carolinas. The storm surge could rise up to 13 feet -- that's water inundating homes up to the first-floor ceiling, the National Hurricane Center said.
• Flight cancellations: At least 800 flights along the US East Coast have been canceled Thursday through Saturday ahead of the storm.
"Our sand dunes are healthy, but they're not going to be able to keep back a wall of water like that," he said. "Flooding is almost guaranteed."
Susan Faulkenberry Panousis has stayed in her Bald Head Island, North Carolina home during prior hurricanes, but not this time. She packed up what she could and took a ferry.
"When that last ferry pulls out ... it's unnerving to see it pull away and know, 'That's the last chance I have of getting off this island,'" she said Wednesday.
Emergencies declared in several states
Officials in several states have declared states of emergency, including in the Carolinas, Georgia, Virginia and Maryland, where coastal areas are still recovering from summer storms.
Florence's expanse even captured the attention of the astronauts and cosmonauts aboard the International Space Station, who have been tweeting pictures of the storm back to Earth.
"Watch out, America! #HurricaneFlorence is so enormous, we could only capture her with a super wide-angle lens from the @Space_Station, 400 km directly above the eye," German astronaut Alexander Gerst tweeted. "Get prepared on the East Coast, this is a no-kidding nightmare coming for you."
Florence is one of four named storms in the Atlantic. Tropical Storm Isaac is forecast to approach the Lesser Antilles Islands on Thursday. Hurricane Helene is veering toward Europe. And newly formed Subtropical Storm Joyce is not expected to threaten land soon.
Those four storms are brewing at the same time Hurricane Olivia is pounding Hawaii.
CNN's Kaylee Hartung, Jason Hanna and Steve Almasy contributed to this report.