Image copyright REUTERS Image caption The recently named storm could drop as much as 20cm of rain on some places in the north-eastern US.
Hurricane Sam has intensified into a powerful Category 4 storm, with superstorm Sandy on the same path a few years ago.
Forecasters predict the storm could make landfall on Saturday as a dangerous category 4 hurricane.
The storm is moving through the mid-Atlantic coast, dumping huge amounts of rain on much of New England.
At 1530 GMT on Friday, it was packing top sustained winds of 145 mph (235 kph) and moving westward at 15 mph (24 kph).
It was the fifth Atlantic hurricane this season to make a Category 4 landfall. The major hurricane was just 12 miles (19km) south-southeast of Cape Hatteras, North Carolina.
Thousands of people were evacuated along the northeast coast on Thursday.
People living on and near coasts should be ready for the storm to bring catastrophic impacts ranging from heavy rainfall and flooding to widespread power outages and severe surf and rip currents, officials said.
Image copyright John_Rogers /AP Image caption Governor Charlie Baker said he is ready to take on the storm ‘with gusto’
Airports in Boston, New York, Philadelphia and other eastern cities cancelled some flights due to the storm.
What’s this got to do with Sandy?
Hurricane Sandy slammed into the Eastern Seaboard just months after a string of eight named storms, including three major hurricanes.
At its peak, Sandy was a superstorm, making landfall in New Jersey with winds that peaked at over 130 mph, a record at the time. The storm killed nearly 200 people and caused over $80bn (£60bn) in damage.
Video caption Sandy before and after: a reconstruction of the storm is available
The bad weather stretched from Florida up through the Carolinas to Maine.
In the densely populated region, the storm killed 51 people, destroyed more than 650,000 homes and businesses and triggered $65bn of damage.
It cost more than $23bn in direct damage in New York and New Jersey alone, according to estimates released last month by CoreLogic, a company that provides analysis of the U.S. housing market.
Nate, the second storm to make landfall this year, was ranked a Category 1 hurricane, barely beating out Sandy.
Image copyright EPA Image caption Red tides killed many swimmers along the east coast this year
Meanwhile, before Sandy struck, weather experts warned about another superstorm brewing in the Atlantic. It became Tropical Storm Ernesto and made landfall as a Category 1 hurricane in the Bahamas. The rain it left behind unleashed waves that breached the levees that protect New Orleans, New Orleans residents had feared after the devastating 2005 Hurricane Katrina.
Then, Sandy started to develop in mid-September, well beyond the Atlantic hurricane season’s peak of 5 August to 31 November.
Sandy was so powerful that it hurled golf ball-sized baseball-sized blobs of water onto the New Jersey coastline.
Just as in the case of Hurricane Sandy, a storm study found that the potent blobs may have come from chemicals in a chemical reaction between salt water and the lighter Earth’s crust, similar to a hydrogen bomb.
What are the other scenarios?
Image copyright EPA Image caption Other catastrophic hurricanes include Hurricane Galveston in 1900 and Hurricane Dolly in 2008
Hurricane Irma struck Cuba on 6 September, killing at least 98 people in the Caribbean and Florida.
In one of the most powerful storms on record, it rerouted itself around the tip of Florida’s west coast, sparing central parts of the state.
Nine months later, Hurricane Maria slammed Puerto Rico, leaving thousands without power and water, and wreaking devastation on the Caribbean island of 3.4 million people.
After three hurricanes spawned by the now-discontinued tropical storm Fay, Hurricane Lee and Hurricane Ike, the National Hurricane Center put out the warnings that, before Sandy, that 16 Atlantic storms were in a “potentially damaging position” on 1 October. The severity of those storms was similar to the worst US weather events from a century ago.
Image copyright WSVN Image caption The island of US Virgin Islands were still in devastation from Hurricane Irma.
Superstorm Sandy is now ranked as the third worst storm to hit the US mainland, just behind 1920’s Halloween storm Hoth and 1938’s Hurricane Hazel.
Hurricane Dolly, with wind speeds of up to 150 mph, killed 23 people on the US Gulf Coast in 2010.