Irene, which had at one time been a major hurricane as it headed toward the U.S., no longer had tropical characteristics.
However, it unleashed furious wind and rain on New York on Sunday, sending seawater surging into Manhattan.
Slowly, the East Coast surveyed the damage, up to $7 billion by one private estimate. For many the danger had not passed: Rivers and creeks turned into raging torrents tumbling with limbs and parts of buildings in northern New England and upstate New York.
"This is not over," President Barack Obama said from the Rose Garden, adding that the public should heed the warnings of local officials in the coming days. He said his administration would continue working with cities and states to ensure they were prepared to respond.
"The impacts of this storm will be felt for some time. And the recovery effort will last for weeks or longer," Obama said.
Flood waters rushed toward lower Manhattan, threatening Wall Street and the heart of the world financial network with devastating damage.
A foot of water rushed over the wall of a marina in front of the New York Mercantile Exchange, and floodwater lapped at the wheel wells of yellow cabs.
But as Sunday wore on, the city appeared to have escaped the worst fears of urban disaster - vast power outages, hurricane-shattered skyscraper windows and severe flooding. At about 11:20 a.m. ET, the city canceled the hurricane warning, and a tropical storm warning went into effect.
By 3 p.m. ET, the evacuation order that covered 370,000 people across the city was lifted.
Bloomberg said the storm inflicted significant damage, with retaining walls collapsing in some places and serious flooding across all the five boroughs.
But "whether we dodged a bullet or you look at it and said, 'God smiled on us,' the bottom line is, I'm happy to report, there do not appear to be any deaths attributable to the storm," the mayor said. He added: "All in all, we are in pretty good shape because of the extensive steps we took to prepare."
According to the National Hurricane Center, Irene's winds fell to 60 mph, below the 74 mph dividing line between a hurricane and tropical storm. The NHC said Irene would weaken as it passed over New England and move over eastern Canada by Sunday night. However, it still remained a massive storm with powerful winds extending more than 300 miles from the center.
As a hurricane, Irene had already unloaded more than a foot of water on North Carolina, spun off tornadoes in Virginia, Maryland and Delaware, and left 4.5 million homes and businesses without power.
Irene has been tied to at least 21 deaths. At least nine were caused by falling trees or car crashes into trees. The deaths attributed to the storm included six in North Carolina, four in Virginia, four in Pennsylvania, two in New York, two in rough surf in Florida and one each in Connecticut, Maryland and New Jersey.
At 75 mph, the storm was a Category 1, the least threatening on a 1-to-5 scale. It was as strong was 100 mph Friday.
Twenty homes on Long Island Sound in Connecticut were destroyed by churning surf. The torrential rain chased hundreds of people in upstate New York from their homes and washed out 137 miles of the state's main highway. In Massachusetts, the National Guard had to help people evacuate. The ski resort town of Wilmington, Vt., was flooded, but nobody could get to it because both state roads leading there were underwater.
The National Hurricane Center said the center of the huge storm reached land near Little Egg Inlet, N.J., at 5:35 a.m. The eye previously reached land Saturday in North Carolina before returning to the Atlantic, tracing the East Coast shoreline.
More than 2 million people in Maryland, New Jersey, North Carolina, Virginia and Delaware were told to move to safer places.
Obama declared emergencies for North Carolina, Virginia, New Jersey, New York, Connecticut and Massachusetts.
Irene was the first hurricane to make landfall in the continental United States since 2008, and came almost six years to the day after Katrina ravaged New Orleans on Aug. 29, 2005. Experts said that probably no other hurricane in American history had threatened as many people.
With constant, heavy rain falling in the nation's largest city, there was nothing left to do in Manhattan but wait. There were sandbags on Wall Street, tarps over subway grates and plywood on windows - at least ones low enough to reach. The subway stopped rolling. Broadway and baseball were canceled.
New York City ordered more than 370,000 people who live in flood-prone areas to leave, including Battery Park City in Lower Manhattan, Coney Island and the beachfront Rockaways. However, a great number appeared to have stayed put.
The city opened nearly 100 shelters with a capacity of 71,000 people.
Among the greatest worries was flooding in lower Manhattan, where the East and Hudson rivers converge with the harbor.
However, two pillars of the neighborhood came through the storm just fine: The New York Stock Exchange said it would be open for business on Monday, and the Sept. 11 memorial at the World Trade Center site didn't lose a single tree.
The city shut down the subways and buses Saturday. The transit system carries about 5 million people on an average weekday, fewer on weekends. This marks the first time the city has shut down the entire subway system because of a natural disaster. Officials on Sunday evening said most subway service would resume Monday morning.
New Yorkers are getting a little help from troops out of the Midwest. Members of the Illinois National Guard and the state's emergency management agency made final preparations in Chicago on Saturday before heading out to New York.
The troops are being stationed across the Eastern Seaboard along with six Blackhawk helicopters and two Chinook choppers.
Illinois Emergency Management personnel are being deployed for two weeks to Westchester, N.Y.
In Prattsville, just southwest of Albany, 21 people were reportedly trapped in a motel as swelling waters from Irene surrounding the building.
According to reports, all the bridges to get out had collapsed. The New York National Guard deployed 129 soldiers and several speed boats to reach the motel.
Among the trapped were two pregnant women, seven toddlers and three babies.
Also in Prattsville, there were an unspecified amount of people trapped on a dead end road that had eroded. Officials said they were not in danger and would be evacuated as soon as resources became available.
Irene caused flooding from North Carolina to Delaware, both from the 7-foot waves it pushed into the coast and from heavy rain. Eastern North Carolina got 10 to 14 inches of rain. North Carolina Gov. Beverly Perdue said Irene inflicted significant damage along the North Carolina coast and some areas were unreachable.
Irene made landfall in North Carolina on Saturday just after first light near Cape Lookout at the southern end of the Outer Banks. Shorefront hotels and houses were lashed with waves, two piers were destroyed and at least one hospital was forced to run on generator power.
Wind and rain knocked out power to more than 210,000 customers along the North Carolina coast. More than 60 shelters have been opened in 26 counties.
Virginia's Hampton Roads area was drenched with at least 9 inches, 16 in some spots.
More than 1 million homes and businesses lost power in Virginia alone, where four people were killed and about 100 roads were closed. Emergency crews around the region prepared to head out at daybreak to assess the damage, though with some roads impassable and rivers still rising, it could take days.
The storm arrived in Washington just days after an earthquake damaged some of the capital's most famous structures, including the Washington Monument. Irene could test Washington's ability to protect its national treasures and its poor.
Irene affects travel plans
Irene stirred trouble at the nation's airports. All flights headed out of Los Angeles International Airport on Sunday to the Northeast were canceled. But as New York's three major area airports reopened, flights were scheduled to take off beginning early Monday.
Airport officials said most travelers made alternate plans, leaving only a few stragglers at the airport Sunday morning.
More than 11,000 flights were canceled nationwide over the weekend. What's worse, once Irene passes, it will probably take several days to clear the backup.
The number of passengers affected could easily be millions because so many flights make connections on the East Coast.
The five main New York-area airports - La Guardia, John F. Kennedy and Newark, plus two smaller ones - waved in their last arriving flights around noon. Many departures were also canceled. However, officials said the three major NYC-area airports will reopen for most flights Monday morning.
Airlines are waiving rebooking fees for passengers who want to delay their flights. Regular schedules should resume Tuesday.
Airlines said passengers should call ahead and make sure they have a confirmed seat before going to the airport.
JetBlue Airways expected to resume flights in New York and Boston around midday Monday.
United and Continental airlines said it would decide on Monday's schedule later Sunday after checking facilities for storm damage.
Impact on Southern California
The impact of Hurricane Irene could be felt in another way in Southern California - it could lead to higher gas prices.
Some East Coast refineries have already begun a partial shutdown of operations. If they shut down completely, it would take several days or even weeks to get up and running again.
While our gas does not come from those refineries, a shutdown would reduce overall supplies, and that could mean higher prices for everyone.
The Associated Press contributed to this report.