The National Hurricane Center in Miami says the eye wall of Category 5 Maria is moving onshore over Dominica.
Forecasters say that the "potentially catastrophic" hurricane with 160 mph winds will likely travel over the Leeward Islands and the extreme northeast Caribbean through Monday night and Tuesday.
The storm was on a path that would take it near many of the islands already wrecked by Hurricane Irma and then on toward Puerto Rico and the Dominican Republic.
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The hurricane was expected to maintain a west-northwest motion for the next several days before a turn toward the north-northwest. The forecast track remained to the east of South Florida Monday.
Maria could hit Puerto Rico and the Virgin Islands Tuesday night and Wednesday.
President Donald Trump approved an emergency declaration for the island and ordered Federal Emergency Management Agency to assist the commonwealth. The declaration authorizes FEMA to coordinate all disaster relief efforts in Puerto Rico.
The U.S. National Hurricane Center said the hurricane is "developing the dreaded pinhole eye."
That's a sign of an extremely strong hurricane likely to get even mightier, said University of Miami hurricane researcher Brian McNoldy. Just like when a spinning ice skater brings in their arms and rotates faster, a smaller, tighter eye shows the same physics, he said.
Maria's eye shrank to a small 10 miles (16 kilometers) in diameter Monday evening.
"You just don't see those in weaker hurricanes," McNoldy said. "It's cranking up the angular momentum."
The U.S. territory on Monday imposed rationing of basic supplies including water, milk, baby formula, canned foods, batteries, flashlights and other items.
Puerto Rico was spared the full brunt of Irma although much of the island had its power knocked out. It hasn't had a direct hit from a Category 4 or 5 hurricane since 1928, NBC News reported.
Hurricane warnings were posted for Puerto Rico, Culebra and Vieques, the U.S. and British Virgin Islands, Guadeloupe, Dominica, St. Kitts, Nevis and Montserrat. A tropical storm warning was issued for Martinique, Antigua and Barbuda, Saba, St. Eustatius, St. Maarten, St. Lucia and Anguilla.
A hurricane watch was also in effect for Saba and St. Eustatius, St. Maarten, St. Martin and St. Barthelemy, Anguilla, and Isla Saona to Puerto Plata.
On Wednesday, Maria was expected to be near or over Puerto Rico, which was spared the full brunt of Irma, although much of the island had its power knocked out. Nearly 70,000 people remain without power, and Gov. Ricardo Rossello on Monday warned of another widespread outage.
"We have an extremely weak infrastructure that has already been hit by one storm," he said. "This is going to be a catastrophic event."
Forecasters said the storm would dump up to 18 inches of rain across Puerto Rico and whip the U.S. territory with heavy winds for 12 to 24 hours.
Rossello said officials had prepared about 450 shelters with a capacity for nearly 68,000 people — or even 125,000 in an emergency. There are still nearly 200 people in shelters from Hurricane Irma. Schools were cancelled for Monday and government employees would work only a half day.
Officials in the Dominican Republic urged people to leave areas prone to flooding and said fishermen should remain in port.
Farther north, long-lived Hurricane Jose continued to head northward off the U.S. East Coast, causing dangerous surf and rip currents. It wasn't expected to make landfall but tropical storm watches were posted along the coast from Delaware to Massachusetts' Cape Cod.
Jose was centered about 230 miles east-southeast of Cape Hatteras, North Carolina, and was in a stationary position. It had maximum sustained winds of 75 mph.
The ocean washed over parts of North Carolina's Outer Banks as Hurricane Jose passed well to the east, and five people were knocked off a coastal jetty in Rhode Island by high surf caused by the storm. Officials said rescuers had to fight through rough surf to load the injured onto stretchers and get them to shore. All five were taken to a hospital with minor and major injuries.
Meanwhile, Tropical Storm Lee weakened into a tropical depression far out in the Atlantic while Hurricane Otis weakened far out in the Pacific. Neither threatened land.
NBC 6 will continue to monitor this and will bring you new developments as we get them.