Tropical Storm Henri hit the north-east with heavy wind and rain as it made landfall on Sunday on the coast of Rhode Island, knocking out power to more than 100,000 homes.
Henri caused deluges that closed bridges, swamped roads and left many people stranded in their vehicles.
The storm was downgraded from a hurricane before reaching New England, leaving many to breathe a sigh of relief. There were few early reports of major damage caused by wind or surf.
But heavy, sustained rain raised concerns about flooding from the storm that threatened to hover over the region before turning to the east and moving out to the Atlantic Ocean on Monday night.
Some of the highest rainfalls were expected inland.
Mr Biden declared disasters in much of the region, opening federal recovery aid.
“We’re doing everything we can now to help those states prepare, respond and recover,” he said.
Mr Biden earlier had offered his condolences to the people of Tennessee after severe flooding from an unrelated storm killed at least 22, including children and elderly people, and left dozens missing.
By Sunday evening, Henri had sustained winds of about 65kph as it moved inland across Connecticut, the National Hurricane Centre said.
When it made landfall near Westerly, Rhode Island, it had sustained winds of about 95kph and gusts of up to 112kph.
Several major bridges in Rhode Island, which connect much of the state, were briefly closed on Sunday, and some coastal roads were nearly impassable.
Westerly resident Collette Chisholm, 20, said the waves were much higher than normal but she was not concerned about her home suffering extensive damage.
“I love storms,” Ms Chisholm said. “I think they’re exciting, as long as no one gets hurt.”
In Newport, Paul and Cherie Saunders were riding out the storm in a home that her family has owned since the late 1950s.
Their basement flooded with 1.6 metres of water during Superstorm Sandy nine years ago.
“This house has been through so many hurricanes and so many things have happened,” said Ms Saunders, 68. “We’re just going to wait and see what happens.”
Rhode Island has been hit by hurricanes and tropical storms periodically, including Superstorm Sandy in 2012, Irene in 2011 and Hurricane Bob in 1991.
The city of Providence sustained so much flooding damage from a hurricane in 1938 and Hurricane Carol in 1954 that it built a hurricane barrier in the 1960s to protect it.
That barrier, and newer gates built near by, were closed for hours on Sunday.
The National Weather Service recorded what could be the wettest hour ever in Central Park, with 50 millimetres of torrential rainfall pelting the park between 10pm and 11pm on Saturday.
Earlier in the evening, thousands attending a Homecoming concert at the park were forced to disperse because of heavy rainfall.
“I call it the wettest hour in New York City, New York, for the record books,” said Dominic Ramunni, a National Weather Service meteorologist in Upton, New York.
The weekend was the wettest two-day period in New York City since Irene swept through a decade ago, said Dominic Ramunni, a National Weather Service meteorologist in Upton, New York.
Some communities in central New Jersey were inundated with as much as 20 centimetres of rain by midday on Sunday.
In Jamesburg, TV video footage showed flooded downtown streets and cars almost completely submerged.
In Newark, public safety director Brian O’Hara said police and firefighters rescued 86 people in 11 incidents related to the storm.
Mr O'Hara said “significant flooding” led to vehicles being submerged in flooded areas.
“This could have been a lot worse, particularly as it relates to wind,” New Jersey Governor Phil Murphy said on Sunday evening.
Connecticut Governor Ned Lamont said Henri was close to being in the “rear view mirror", but there was still work to do, even as mandatory evacuations were ended in some communities.
Earlier in the day, about 250 residents from four nursing homes on the shoreline were relocated.
The forecast had some fearing the worst effects of the rain were still to come in a region where the ground in many areas is saturated from recent rains.
Marshall Shepherd, director of atmospheric sciences at the University of Georgia and former president of the American Meteorological Society, said Henri was reminiscent of Hurricane Harvey, a slow-moving storm that hit the Houston area in 2017.
“To the west side of the storm, you have a banding feature that has literally been stationary, sitting there and dumping rain. That will be a significant hazard for the New York and New Jersey area,” Mr Shepherd said.
After Tropical Storm Irene roared up the coast in August 2011, many were relieved when the New York City area largely was spared.
But then the storm settled over the Green Mountains and Irene became the biggest natural disaster to hit Vermont since an epic 1927 flood.
Parts of the state had 280mm of rain in just 24 hours. Irene killed six in Vermont, left thousands homeless, and damaged or destroyed more than 200 bridges and more than 800km of motorway.
“I remember Irene and media outlets outside Vermont brushing it aside as if no big deal while it hit Vermont,” Robert Welch, a podcaster, tweeted Sunday.
“I’ll relax when I see it at sea on radar.”
By Sunday afternoon, power cuts affected more than 78,000 customers in Rhode Island, 32,000 in Connecticut, 9,000 in Massachusetts and 4,000 in New York.
In one of his final appearances as governor before he steps down over a sexual harassment scandal, New York Governor Andrew Cuomo said the state’s main concern was inland areas such as the Hudson River Valley, north of New York City.
“In the Hudson Valley you have hills, you have creeks, the water comes running down those hills and turns a creek into a ravaging river,” Mr Cuomo said.
“I have seen small towns in these mountainous areas devastated by rain. That is still a very real possibility.”
Major airports in the region remained open as the storm approached, although hundreds of Sunday’s flights were cancelled.
Service on some branches of New York City’s commuter rail system was suspended through Sunday, as was the Amtrak service between New York and Boston.
Norbert Weissberg watched the waves from the edge of the parking lot at a beach in East Hampton as strong winds whipped an American flag flying from an unmanned lifeguard chair.
“I’m always excited about seeing something as ferocious as this,” Mr Weissberg said.
“It’s less ferocious than I thought. We’re all geared up for a major, major calamity and it’s a little less than that.”