Charleston, South Carolina (CNN) A deluge roared over the East Coast on Saturday, causing blackouts and evacuations and threatening all-time rainfall records in South Carolina and the southern Appalachians.

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.

Photos: Storms flood East Coast Photos: Storms flood East Coast This aerial photo shows flooding around Aberdeen Country Club in Longs, South Carolina, on Tuesday, October 6. South Carolina experienced record rainfall amounts over the weekend, forcing hundreds of evacuations and rescues. Hide Caption 1 of 37 Photos: Storms flood East Coast A woman uses her boat to check on neighbors and see if they want to evacuate in Summerville, South Carolina, on Monday, October 5. Hide Caption 2 of 37 Photos: Storms flood East Coast Police officers carry a woman to dry land after she was rescued from her home in the St. Andrews area of Columbia, South Carolina, on October 5. Hide Caption 3 of 37 Photos: Storms flood East Coast Neighbors and friends help clean up a home affected by flooding in Columbia on October 5. Hide Caption 4 of 37 Photos: Storms flood East Coast Five-month-old Jeremiah Odum, left, and his 2-year-old brother, Braxton Odum, nap on a cot in a high school gymnasium being used as a Red Cross shelter for flood evacuees in Rowesville, South Carolina, on October 5. Hide Caption 5 of 37 Photos: Storms flood East Coast Rescue teams wait for an emergency vehicle in the Forest Acres neighborhood of Columbia on Monday, October 5. Hide Caption 6 of 37 Photos: Storms flood East Coast An oil sheen floats atop floodwater in a subdivision west of the Ashley River in Charleston, South Carolina, on October 5. Hide Caption 7 of 37 Photos: Storms flood East Coast A dog is cut off from its home in Florence, South Carolina, on October 5. Florence is about 85 miles east of the capital city, Columbia. Hide Caption 8 of 37 Photos: Storms flood East Coast Hunter Baker drives his boat down a flooded East Black Creek Road to his home following heavy rains in Florence on October 5. Hide Caption 9 of 37 Photos: Storms flood East Coast A man makes his way through floodwaters in the parking lot of The Citadel Beach Club on Isle of Palms, South Carolina, on October 5. Charleston and surrounding areas are still struggling with flooding, as are areas 100 miles inland. Hide Caption 10 of 37 Photos: Storms flood East Coast Members of Norfolk Fire-Rescue pull a man from his car in Norfolk, Virginia, on Sunday, October 4. Hide Caption 11 of 37 Photos: Storms flood East Coast David Linnen takes a yard rake to clear drains in front of the Winyah Apartments in Georgetown, South Carolina, on October 4. Hide Caption 12 of 37 Photos: Storms flood East Coast Charlene Stennis is escorted to safety after her son was rescued from a stranded vehicle during the heavy rains on October 4 in Columbia, South Carolina. Hide Caption 13 of 37 Photos: Storms flood East Coast The roof of a submerged vehicle peeks above the flood waters on October 4 in Columbia, South Carolina. Hide Caption 14 of 37 Photos: Storms flood East Coast Tripp Adams, 8, walks through flood waters in Georgetown, South Carolina, on October 4. Hide Caption 15 of 37 Photos: Storms flood East Coast A person walks through the flooded Market and Water streets in downtown Wilmington, North Carolina, on October 4. Hide Caption 16 of 37 Photos: Storms flood East Coast Neighbors watch employees with the city of Isle of Palms, South Carolina, cut a live oak tree that fell after heavy rain on October 4. Hide Caption 17 of 37 Photos: Storms flood East Coast A man watches as a vehicle tries to navigate flood waters in Florence, South Carolina, on October 4. Hide Caption 18 of 37 Photos: Storms flood East Coast Two men row a boat on a flooded street in downtown Charleston, South Carolina, on October 4. Hide Caption 19 of 37 Photos: Storms flood East Coast Police block an entrance to Highway 17 in Charleston, South Carolina, on October 4. Hide Caption 20 of 37 Photos: Storms flood East Coast A man paddles up to a flooded store in Columbia, South Carolina, on October 4. Hide Caption 21 of 37 Photos: Storms flood East Coast A firefighter walks down a flooded street in downtown Charleston, South Carolina, on October 4. Hide Caption 22 of 37 Photos: Storms flood East Coast A worker cleans a drain on a flooded street in downtown Charleston, South Carolina, on Saturday, October 3. Hide Caption 23 of 37 Photos: Storms flood East Coast A utility worker examines the damage to a home Charlotte, North Carolina, on October 3. Hide Caption 24 of 37 Photos: Storms flood East Coast A motorist turns back as floodwater rises in Harrisburg, North Carolina, on October 3. Hide Caption 25 of 37 Photos: Storms flood East Coast A woman walks through One City Plaza in downtown Greenville, South Carolina, as rain and wind pound the area on October 3. Hide Caption 26 of 37 Photos: Storms flood East Coast Bob Ashbaugh, from Pittsburgh, takes video of waves crashing over homes at risk from erosion during high tide in Isle of Palms, South Carolina, on October 3. Hide Caption 27 of 37 Photos: Storms flood East Coast Stuart Tait ties together wood after his house collapsed into an inlet on Grassy Sound during high tide on October 3 north of North Wildwood, New Jersey. Hide Caption 28 of 37 Photos: Storms flood East Coast Will Cunningham, 14, rides his bike down Station 29 on Sullivan's Island, South Carolina, ahead of his paddling friend Patrick Kelly, 14, on October 3. Hide Caption 29 of 37 Photos: Storms flood East Coast Paul Banker paddles a kayak as his wife, Wink Banker, takes photos on a flooded street in Charleston, South Carolina, on October 3. Hide Caption 30 of 37 Photos: Storms flood East Coast Up to 4 inches of rain could strike the waterfront between Georgia and New Jersey. Motorists deal with the conditions on Friday, October 2, in Seaside Heights, New Jersey. Hide Caption 31 of 37 Photos: Storms flood East Coast Workers install a flood barrier at the entrance to the Market Pavilion Hotel in downtown Charleston, South Carolina, on Friday, October 2. Parts of the South Carolina coast braced for likely flooding. Hide Caption 32 of 37 Photos: Storms flood East Coast Flooding engulfs a neighborhood in the Strathmere section of Upper Township, New Jersey, on October 2. Hide Caption 33 of 37 Photos: Storms flood East Coast Sandbags surround a building in Old Town Alexandria, Virginia. Hide Caption 34 of 37 Photos: Storms flood East Coast A man closes a storefront on October 2 in Seaside Heights, New Jersey. Hide Caption 35 of 37 Photos: Storms flood East Coast Floodwater rises along Central Avenue in Sea Isle City, New Jersey, on October 2. Hide Caption 36 of 37 Photos: Storms flood East Coast Cars negotiate flooded streets on October 2 in Midland Beach on Staten Island, New York. Hide Caption 37 of 37

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

Daily Rainfall Total Today (so far): Downtown Charleston : 6.04 inches - broke previous record of 3.48 inches set in 1994 #chswx — NWS Charleston, SC (@NWSCharlestonSC) October 3, 2015

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."

Due to the flood we will be closed today. Photo @postandcourier A photo posted by @holycityconsignment on Oct 3, 2015 at 7:40am PDT

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.

Never a boring day in Charleston when it floods. #classescancelled #jeep #lifted A video posted by Claudio Miro (@papomiro) on Oct 2, 2015 at 7:45am PDT

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.

While Hurricane Joaquin is predicted to miss the U.S., water connected to the storm is feeding torrential rain on the East Coast.

"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.