Three people died on Friday and Saturday in traffic incidents in South Carolina, and a car passenger died in North Carolina on Thursday when a tree fell on Interstate 95, officials said. The deaths were blamed on the weather.
The potentially historic precipitation will last all 48 hours of the weekend, due to a 1-2 punch from Hurricane Joaquin over the open Atlantic and a second weather system: Joaquin drenches the Northeast and a separate low-pressure rainmaker dumps on the Southeast.
As if one wasn't bad enough.
President Barack Obama declared an emergency in South Carolina, authorizing federal aid, and parts of the state's coast braced for likely flooding with more than 15 inches of rain.
In Charleston, people paddled kayaks and canoes down city thoroughfares as more than 6 inches of rain fell in downtown on Saturday, according to the National Weather Service Twitter account.
"What we're experiencing is an unprecedented event," said Mayor Joseph Riley Jr., referring to record rainfalls and extremely high tides happening at the same time, according to CNN affiliate WCBD
Lauren Tuorto closed her Holy City Consignment shop on the Charleston peninsula until Tuesday.
"It is impossible to navigate the peninsula right now without a kayak or a monster truck," she said.
"Having weathered plenty of hurricanes in the Out Islands of the Bahamas where my family lives and living in Charleston for 10 years, I have never seen rainfall like this," she said.
In tourist destination Myrtle Beach, water began to swallow a substation, causing power outages in the area, according to CNN affiliate WBTW.
"I'm a good citizen and I'm going to obey," Shirley Jones, of Charleston, said of official advisories to stay home and out of the knee-deep water. "I'm going to hole up in my apartment and clean out my dresser."
As South Carolina residents hunkered down, up to 500 residents were evacuated in coastal Brunswick County, North Carolina, that state's governor said.
Flood and flash flood watches are posted from Georgia to Delaware through at least Sunday.
"The magnitude of rainfall coupled with already-wet soil will bring about the threat of potential significant flooding impacting life and property," CNN meteorologist Michael Guy said. "There is also and increased threat of landslides and debris flows across the mountains and foothills of the Carolinas.
"Life-threatening rip currents, high surf, and coastal flooding, mainly at high tides, will stretch nearly the entire eastern U.S. coast," he added, noting wind gusts that could reach 30 mph and could topple trees.
A foot of rain could befall the Southern Appalachians. The Northeast could see two inches. And up to four inches could strike the waterfront between Georgia and New Jersey.
The low pressure over the Southeast is funneling a deep atmosphere river of tropical moisture into the Carolinas, creating the torrential rainfall, CNN meteorologist Sean Morris said.
While it appears Joaquin won't make a direct hit on U.S. mainland, communities from the Southeast to New England still had their gutters full.
Meanwhile, Joaquin strengthened and returned to its prior monster status: a Category 4 hurricane with 130 mph winds. It was between Bermuda and the Bahamas' San Salvador Island as of midday.
"This is not just any rain," Gov. Nikki Haley of South Carolina said. "This is going to be the heaviest rain we have ever seen."
Added Gov. Pat McCrory of North Carolina: "The tough news for North Carolina and especially South Carolina is continued rain."
McCrory expressed appreciation for how Joaquin didn't slam into the eastern seaboard as earlier feared.
"It could have been much worse if that hurricane shifted to the west," McCrory told CNN.
Both Carolinas, New Jersey, and Virginia declared states of emergency.
The National Weather Service warned that some places could see as much as 12 inches of rain.
Flooding is a major concern for a number of reasons: directly from all the rains, indirectly from rivers and creeks possibly overflowing their banks, and also from storm surges fanned by strong winds. Beaches off New Jersey and Delaware, for instance, had seen around 50 mph gusts by Friday.
Compounding this is the fact that the region was already drenched.
"We've gotten into this pattern of lows in the Mid-Atlantic, which has had lots of rain the last two weeks," CNN meteorologist Rachel Aissen said. "So the ground is just saturated."
'Squeezing effect' for rains, winds
A few days ago, some forecasters thought that Hurricane Joaquin could make landfall over the weekend in Virginia or somewhere in that vicinity. The fear was that this could be another Superstorm Sandy -- an October storm that barrels up from the Caribbean with high winds, heavy rains and deadly flooding.
Such an extreme seems unlikely now, though it doesn't mean history won't be made.
Aissen explained that a combination of factors, including a high-pressure system behind the system, are helping push Joaquin away from the U.S. coast. At the same time, they're making the system now parked there more dangerous.
"It's creating a squeezing effect that is just ushering both moisture and high winds," said the CNN meteorologist, explaining that the winds are more a worry -- not due to the damage they can do themselves, but how they might rustle up storm surges.
In an anticipation of that wet reality, Friday night football games were moved up a day over flooding concerns in South Carolina's Lowcountry region, while others were postponed. The Yankees-Orioles game in Baltimore and the Marlins-Phillies showdown in Philadelphia were both postponed due to rain.
Farther north, New Jersey Gov. Chris Christie warned that -- hurricane or not -- there could be flooding in the southern counties of Cape May, Atlantic, Cumberland and Salem.
Said New York Gov. Andrew Cuomo: "We're not getting complacent, because weather reports change. We're making sure that everything is ready to go, just in case."
Along Virginia Beach's Atlantic Avenue, a main thoroughfare about two blocks from the ocean, business owners appeared to be taking a wait-and-see approach on Friday.