CNN  — 

Parts of the Northeast began to feel Hurricane Henri’s first impacts Saturday evening as the storm barreled toward the coast ahead of an anticipated Sunday landfall, threatening to bring damaging winds, dangerous storm surge and flooding to an already saturated area.

The storm’s first showers drifted from southern New Jersey and into the northern part of the state Saturday evening and began soaking parts of southwestern New York, heading toward New York City, CNN meteorologist Gene Norman said.

“This rain band could produce rainfall rates of 1-3” per hour this evening into the overnight hours, with considerable flash flooding possible,” the National Weather Service of the Eastern Region said on Twitter.

In addition to the rain, coastal flooding is expected in parts of New Jersey and Delaware’s coasts with Saturday evening’s high tide, the weather service in Mount Holly said on Twitter.

Henri, which strengthened from a tropical storm late Saturday morning over the Atlantic, could make landfall at or near hurricane strength on New York’s Long Island or southern New England on Sunday, the National Hurricane Center said.

Strong wind and rain will likely smack a broad area from New York City into New England – and since the area is saturated from recent rain, Henri could easily down trees and set up days of power outages.

New York City Mayor Bill de Blasio declared a state of emergency Saturday afternoon ahead of the storm, saying in a news conference that heavy wind, rain and storm surges are expected Sunday morning and urged everyone to stay indoors if they can.

The mayor also issued a travel advisory, recommending that residents limit travel on Sunday, especially driving.

And New York Gov. Andrew Cuomo warned people in flood-prone areas: Move to safety now.

“If you know you are in an area that tends to flood … get out of that area now, please,” Cuomo said in a televised news briefing Saturday. “If you have to get to higher ground it has to be today.”

Lightning also forced the postponement of the “WE LOVE NYC: The Homecoming Concert,” which was televised by CNN.

Mandatory evacuations ordered

More than 35 million people are under a flood watch across the Northeast, with the hurricane center warning the heavy rain could cause “considerable flash, urban and small stream flooding” and create the potential for “widespread minor and isolated moderate river flooding.”

The Weather Prediction Center has a moderate – a level 3 of 4 – risk for excessive rainfall for parts of western Connecticut and Massachusetts, southern New York, northeastern Pennsylvania and northern New Jersey.

Significant damage is possible in this already-soaked region even if Henri is not a hurricane at landfall, Federal Emergency Management Agency administrator Deanne Criswell said.

“We’re going to see power outages, we’re going to see downed trees, and even after the storm has passed, the threat of falling trees and limbs is still out there,” Criswell told CNN Saturday morning.

In Connecticut, mandatory evacuations were ordered for the coastal towns of Guilford and Branford, according to a tweet from state Rep. Sean Scanlon.

“If you live in a coastal, low-lying or area prone to historic flooding due in Guilford, evacuate now. If you live in Zone 1 or 2 in Branford (see map), evacuate by 9pm,” Scanlon wrote. “PLEASE TAKE THIS SERIOUSLY.”

Groton Mayor Keith Hedrick also told CNN the city decided to order mandatory evacuations in some neighborhoods, and authorities will go door-to-door in those parts of town to advise residents to leave ahead of the hurricane.

Earlier Saturday, the city recommended a voluntary evacuation for some residents by 10 p.m., including those who live on Shore Ave., Beach Pond Road, Pine Island Road and Jupiter Point.

Connecticut Gov. Ned Lamont told residents Saturday afternoon to prepare to shelter in place on Sunday and urged them to pile up on food and get extra gasoline. Energy company Eversource said Saturday between 50% and 69% of customers in Connecticut could lose power and restoration efforts could take up to three weeks.

Millions under weather warnings

Henri’s center had sustained winds of 75 mph late Saturday afternoon.

Rain showers will likely become more widespread starting Saturday night and into Sunday, when Henri is expected to make landfall.

The storm will likely slow its forward speed after landfall, meaning the risk for showers and isolated thunderstorms will remain through Tuesday morning in the Northeast.

Hurricane warnings have been issued for nearly 6 million people in areas including parts of Long Island, and from New Haven, Connecticut, to west of Westport, Massachusetts.

More than 36 million other people are under tropical storm warnings, including parts of New Jersey and New York – including New York City – and large parts of southern New England.

A hurricane landfall in this region would be somewhat rare. Long Island has not had a direct hurricane hit since Gloria in 1985; New England last saw a hurricane landfall with Hurricane Bob in 1991.

Superstorm Sandy made landfall in New Jersey in 2012 with hurricane force winds and devastated swaths of the Northeast, though it technically was a post-tropical cyclone when it came ashore. Henri’s wind field at landfall is expected to be a quarter of the size, CNN meteorologists said.

Long Island restaurateur: ‘We have some big concerns’

With Henri, storm surges also are a major concern: Surges between 3 and 5 feet are possible Sunday in areas including parts of Long Island to Chatham, Massachusetts, the hurricane center said.

People living in an area under storm surge warnings “should take all necessary actions to protect life and property from rising water and the potential for other dangerous conditions,” the hurricane center said Saturday morning.

On Long Island’s East End, Christine Oakland-Hill said road flooding was just one of her concerns for her shoreside business, Oakland’s Restaurant and Marina, which has been there 30 years.

“God forbid this is head on,” Oakland-Hill told CNN affiliate WCBS on Friday. “We have some big concerns. This (business) is our legacy.”

Doreen Puco was running errands at Long Island’s Oyster Bay to prepare for the storm.

“I’m afraid of losing my power,” Puco told WCBS Friday. “I just hope they’re better prepared than they have been in the past.”

James Masog, center, and Gary Tavares move particle board into place to board up the sliding glass doors of a client's house in Charlestown, Rhode Island, on Saturday.

Portions of New England and southeast New York could see widespread rainfall of 3-6 inches through Monday, with isolated totals near 10 inches possible – and could lead to flash, urban and stream and river flooding.

As Henri moves parallel to the East Coast on Saturday, rip currents also will be a concern from North Carolina to Massachusetts.

More than 50 rescues from rip currents were reported in North Carolina’s coastal Wilmington area alone on Friday, the National Weather Service in that city said.

Forecast rainfall from Hurricane Henri.

One city will order mandatory evacuations

New York, Massachusetts, Connecticut and Rhode Island officials said National Guard members were activated or otherwise poised ahead of the storm to help with any rescues, cleanup and other support.

Massachusetts Gov. Charlie Baker warned residents to be prepared for possible prolonged power outages, minor flooding and tropical-storm-force winds and urged people to avoid unnecessary travel and to delay weekend getaways to Cape Cod.

In a news conference Saturday afternoon, Baker said that while the state will “avoid the direct hit,” it will likely still feel impacts including the outages, winds, storm surge and significant rainfall. He warned there is a chance of flooding and washed-out roads in Berkshire and Worcester counties, especially given the previous rainfall.

“Looks like we will avoid the worst,” the governor said. “But everyone should still pay attention to local weather alerts.”

Cuomo said Saturday he would declare an emergency for areas including Long Island, New York City, Westchester and Hudson Valley.

New York has heavy equipment deployed on Long Island and water-rescue teams ready to go, Cuomo said.

A voluntary evacuation order is in place in Fire Island – a barrier island off the southern shore of Long Island – so residents and visitors can “leave for their own safety,” Suffolk County Executive Steve Bellone said in a Saturday afternoon tweet.

“I urge residents to check ferry service times and make plans to leave the barrier island today,” Bellone wrote.

New York City Emergency Management issued a travel advisory for the city until further notice. All beaches in the city will close Sunday and Monday, according to city officials. Swimming and wading will not be permitted during those days.

New York City’s Metropolitan Transportation Authority (MTA) suspended service on its Long Island Rail Road (LIRR) Saturday night and Metro-North Railroad (MNR) on Sunday due to the impacts of the storm, the transportation service said in an update.

And Amtrak announced Saturday it has canceled its service between New York and Boston on Sunday, according to the passenger railroad service. Train service between New Haven, Connecticut, and Springfield, Massachusetts, is also suspended.

Rhode Island Gov. Dan McKee urged residents to prepare for the storm and announced he has signed an emergency declaration to unlock federal resources to support storm response.

A town employee in Bourne, Massachusetts, connects a generator to a sewage pump in the case of electrical loss as Henri approached Friday.

The governor urged residents to use caution along shoreline areas due to anticipated rip currents and high surf.

“Rhode Island has often experienced needless tragedy during storms when wave watchers and anglers who have climbed onto rocks near the shore get hit by waves and quickly swept out to deep water and drowned,” he said.

State beaches and parks will be closed Sunday and likely Monday, depending on storm damage and required clean up.

CNN’s Brandon Miller, Artemis Moshtaghian, Brian Todd, Haley Brink, Arlette Saenz, Liam Reilly, Hollie Silverman, Melissa Alonso, Jackson Dill, Elizabeth Joseph, Judson Jones and Raja Razek contributed to this report.