The sluggish storm, now moving east at just 1 mph, is notable for the epic amounts of rain it has dumped, still keeping the region on the alert for possible flash flooding.
In hard-hit New Jersey, moderate river flooding is occurring along the Saddle River at Lodi and will continue until late tonight, as well as the Pequannock River below Macopin Dam until Tuesday evening and the Millstone River at Blackwells Mills until Wednesday morning.
Heavy rain across the area could add up to 3 inches to the 1 to 2 inches that fell on Sunday.
Henri's track shifted east Sunday, which spared eastern Long Island a dreaded direct hit, making landfall near Westerly, Rhode Island at 12:15 p.m. as a weakened storm, but that hardly diminished the dangers from Henri, which is hammering several states with heavy rain and flooding.
The storm is expected eventually to turn east and head out to the Atlantic Ocean on Monday night.
Gov. Andrew Cuomo likened the scenario facing areas north of the city not to Superstorm Sandy but to Hurricane Irene in 2011, which largely spared the city but brought copious rain to the Catskills, causing catastrophic damage.
"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. I have seen small towns in these mountainous areas devastated by rain. That is still a very real possibility," Cuomo said.
Here are some key forecast points:
* Major flash flooding will persist over the Northeast.
* Widespread rainfall of 3-6" is forecast in the path of Henri with localized higher amount possible.
* The highest amounts are likely across the Lower Hudson Valley, NY, Western CT, Northeast NJ and NYC.
* Rivers and streams may rapidly overflow in places with life-threatening flash flooding prompting evacuations and water rescues.
President Joe Biden declared disasters in much of the region, opening the purse strings for federal recovery aid. The White House said Biden discussed preparations with northeastern governors and that New York Lt. Gov. Kathy Hochul, who succeeds Cuomo on Tuesday, also participated.
Major airports in the region remained open as the storm approached, though hundreds of Sunday's flights were canceled. Service on some branches of New York City's commuter rail system was suspended through Sunday, as was Amtrak service between New York and Boston.
Even before Henri's arrival, heavy rain and thunderstorms connected to Henri unleashed flash floods across the New York City area Saturday evening and early Sunday morning, giving the region a taste of the troubles ahead. Central Park, where the much-vaunted Homecoming concert had to be canceled midway because of the inclement weather, saw more than 4 inches of rain, and the highest amount of rain ever to fall in a single hour in New York City, 1.94 inches.
RELATED: What is storm surge and why is it dangerous?
The current guidance from the National Hurricane Center:
1. Dangerous storm surge inundation is expected to continue today in portions of Long Island, Connecticut, Rhode Island, and southeastern Massachusetts, where a Storm Surge Warning has been
issued. Residents in these areas should follow any advice given by local officials.
2. Tropical storm conditions will continue in portions of the tropical storm warning area into tonight.
3. Heavy rainfall may lead to considerable flash, urban, and small stream flooding, along with the potential for widespread minor to isolated moderate river flooding over portions of Long Island, New England, eastern New York, New Jersey and northeast Pennsylvania.
4. Swells from Henri will continue to affect much of the east coast of the U.S. during the next day or so. These swells could cause life-threatening surf and rip currents.
Additional Henri Coverage
Tracking Henri Live
Long Island prepares for Henri
Connecticut braces for Henri
How mass transit is preparing for Henri
New York City beaches closed Sunday and Monday
What is storm surge and why is it dangerous?
Emergency Resources for severe weather
Weather or Not with Lee Goldberg's extreme weather survival guide
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The Associated Press contributed to this report