A paralyzing snowstorm is walloping the tri-state with blinding snow and icy winds, and New York, New Jersey and Connecticut are under states of emergency as nearly 20 inches of snow was forecast to be dumped on parts of the region.

Eastern Long Island was hit the hardest early in the storm: Islip Airport had 14.7 inches of snow by 3 a.m. Tuesday, and Upton had 12.1 inches. In New York City, Queens was seeing the most snow, with 10.1 inches of snow on the ground in Jamaica by 3:15 a.m. Central Park had 6.3 inches of snow by 1 a.m.

A blizzard warning remained in effect for Suffolk County as of 5:30 a.m. The blizzard warning was cancelled for all other counties, including in New York City.

The New York City subway and bus system shut down at 11 p.m. Monday after a National Weather Service blizzard warning went into effect for New York City. MTA officials initially believed they could keep the underground subway service running through the blizzard, but Gov. Cuomo said worsening conditions necessitated the closure.

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All non-emergency vehicles were also ordered off state highways and all local streets and roads in New York south of Ulster county beginning at 11 p.m.

Cuomo said motorists were stranded on snowy roads for 24 hours in other storms.

"We learned the lesson the hard way," he said Monday afternoon. "We'd rather be safe than sorry."

Similar travel bans are in place in New Jersey and Connecticut. Metro-North, PATH and New Jersey Transit also shut down at 11 p.m.

The evening rush was effectively moved up by several hours as offices closed early and workers were sent home. The Long Island Rail Road and Metro-North added extra trains in the afternoon to accommodate the early rush, and supermarkets in New York City were wiped of inventory as last-minute shoppers got in line to stock up on food and emergency supplies.

"This will most likely be one of the largest blizzards in New York City history," Mayor de Blasio said. "It is not business as usual."

Conditions began to deteriorate later in the evening, with snow falling as quickly as 2 to 4 inches per hour, according to Storm Team 4. Lightning and thunder may accompany the snow during the most intense part of the storm overnight. Sustained winds of 30 to 40 mph with gusts as high as 50 mph will create whiteout conditions across the region.

The heaviest snow and the strongest winds should wind down by 7 a.m. Tuesday, and the snow will taper by lunchtime, according to Storm Team 4.

Snowfall projections were greatly reduced by early Tuesday morning. By the time the blizzard is over, between 4 and 8 inches of snow are expected to be on the ground in New York City. Up to 20 inches of snow are possible in eastern Suffolk County. Areas further west should get 3 to 6 inches.

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Most of the waterfront counties in New York, New Jersey and Connecticut are under coastal flood watches or warnings from Monday night into early Tuesday.

There were some scattered reports of outages late Monday. One residence hall at Stony Brook University had power knocked out at about 10:30 p.m., affecting 1,500 people, according to campus police. Students were provided temporary shelter, and the minor outage was expected to be "remedied quickly."

Drivers on Long Island flocked to gas stations early Monday to fuel their vehicles and fill up gas cans for generators before the blizzard. Some stations in Hicksville and Bethpage were already out of gas, and one attendant said he had been pumping gas nonstop since 6 a.m., pumping more in three hours than he typically does in a half day.

Hotel rooms booked quickly as travelers became stranded in the area. One Marriott hotel manager told NBC 4 New York her chain of hotels with the company had no vacancies within a six-mile radius of LaGuardia Airport.

More than 7,700 flights in and out of the Northeast were canceled, and many of them may not take off again until Wednesday. Passengers on at least one outbound Virgin Atlantic flight were stranded on the tarmac at Kennedy Airport for about six hours before being stuck back at the terminal after midnight, according to NBC News.

The largest snowstorm recorded in the city was a February 2006 storm that dumped 26.9 inches on Central Park.