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Flash floods, 'once in 200 years rainfall event' loom in South Carolina

Around 22 million Americans were under flood watches early Saturday as a "once in 200 years rainfall event" started drenching South Carolina.

About 22 million Americans along the East Coast were under flood watches Saturday as a "once in 200 years rainfall event" began hammering the Carolinas with heavy rains — and the worst was yet to come.

South Carolina could get more rain in three days than it normally does during the entire fall, The Associated Press reported. Saturday was the third consecutive day of a relentless onslaught of rain, with a plume of precipitation expected to last through the weekend and only begin to taper off Monday.

RELATED: Cargo ship vanishes in Hurricane Joaquin

Waterlogged Charleston, South Carolina, received 6 inches of rain over a period of 12 to 18 hours, NBC News meteorologist Bill Karins said on MSNBC, adding that people there were paddleboarding through the city. Flash flood warnings were issued for downtown Charleston.

"A lot more damage is still yet to be done," he warned. "The rivers are going to be a problem in this area for days to come."

President Obama declared a state of emergency in South Carolina and ordered federal aid for the Palmetto state.

With a tide of 8.2 feet, water levels in Charleston were the highest they had been since 2009. North of Myrtle Beach, residents received 16 inches of rain. A whopping 2 feet of rain threatened other areas in the state.

As much as a foot of rain fell overnight in Wilmington, North Carolina, and numerous water rescues were reported.

"Our goal constantly is to be overprepared and underwhelmed," North Carolina Gov. Pat McCrory told reporters Saturday morning.

North Carolina officials reported about 10,000 power outages in the state mid-afternoon Saturday. So far, one North Carolina resident had been killed in the weather: A woman driving on Interstate 95 died when a tree fell on her car Thursday.

In South Carolina, more than 4,700 power outages were reported.

"We're more concerned about what could happen tonight if there's another wave," Greenville, South Carolina, Mayor Knox White told NBC News. "If it gets worse, that could be another story."

Elsewhere on the East Coast, soggy weather was also causing misery: Storms in New Jersey were so severe, they ripped a home off its foundation in Wildwood along the Jersey Shore.

Officials in Delaware were monitoring high tides and wind gusts of up to 40 mph. About 145 flights nationwide were canceled.

But the Carolinas have been getting the brunt of the nasty weather, which forecasters said could have been exacerbated if Hurricane Joaquin made landfall in the U.S. as initially anticipated. Joaquin, a restrengthening Category 4 storm with 155 mph winds, battered the Bahamas but was moving out to sea Saturday.

Karins said the National Weather Service was referring to the historic drenching in South Carolina this weekend as a "once in 200 years rainfall event" — and it had the potential to be as bad as any likely to occur every 500 years.

The NWS added that "record rainfall and life-threatening flash flooding" were possible through Sunday. Up to 15 inches of rain was possible in some parts of the Carolinas, forecasters warned.

This stretch of the East Coast from Charleston to Washington, D.C., is expected to be deluged as a result of a weather pattern called a "Rex Block," which is forecast to bring heavy rain to the area's already-oversaturated grounds.

This "powerful" low-pressure system over the southeast is moving slowly northeast, carrying heavy rainfall and expectations for high tides, the NWS said.

By 8 a.m. ET, police said no flood-related injuries had been reported in Charleston.

The NWS predicted "several rounds of abnormally high tides" in South Carolina and Georgia from Friday night through Sunday. "The highest tides are expected early Saturday afternoon, potentially into Saturday night," it added.

"Periods of heavy rain will affect southern South Carolina and eastern portions of Georgia," the NWS said. "There is increasing confidence that a significant heavy rainfall event will occur through Sunday with some locations seeing record rainfall amounts."

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