Hurricane Earl strengthened overnight and is expected to skirt the Outer Banks of North Carolina tonight, as evacuations continue and Labor Day plans are in jeopardy for vacationers up and down the East Coast.

As of this morning, Earl was a powerful Category 4 hurricane, with maximum sustained winds of 145 mph, according to the National Hurricane Center.

Evacuations were ordered Wednesday for Hatteras and Ocracoke Islands in the Outer Banks. North Carolina Gov. Bev Perdue and Virginia Gov. Bob McDonnell have declared a state of emergency.

"On the track that we're forecasting, there will be a significant impact to the Outer Banks," Todd Kimberlain, a hurricane specialist at the center, said today in an interview with Bloomberg. "They have less than 24 hours before the arrival of hurricane conditions. There isn't a whole lot more time and conditions are going to deteriorate throughout the day."

Hurricane and tropical storm watches and warnings now stretch from North Carolina to Maine in the U.S. and Nova Scotia in Canada. Hurricane watches were issued today in Massachusetts for north of Sagamore Beach to Plymouth, and west of Woods Hole to Westport. A tropical storm warning was issued for a portion of New York's Long Island.

The center's forecast map shows Earl tracking northeast after brushing North Carolina, coming close to New England late Friday.

Many industry trade associations are sending out advisories such as this one.

"It wouldn't take much of a deviation for the core of the hurricane to be very close to Martha's Vineyard, Nantucket, and maybe even Cape Cod," Kimberlain said.

The hurricane is expected to pass about 50 miles from Nantucket.

Tropical storms Fiona and Gaston are tracking behind Earl, although neither is an immediate threat to the U.S. coast.

Fiona, with maximum sustained winds of 60 mph, is moving northwest and projections from the hurricane center show the storm staying well offshore in the Atlantic. A tropical storm watch is in effect for Bermuda.

Gaston, with maximum sustained winds of 40 mph, is moving slowly over the central tropical Atlantic with no gain in strength, the hurricane center said. There are no watches or warnings associated with this storm.