Print edition: 
CHICAGO — Hurricane Earl quickly gathered strength Monday, becoming a dangerous Category 4 storm as it roared past Puerto Rico and the U.S. Virgin Islands.
Meteorologists warned that Earl is likely to intensify and remains a threat to travelers and businesses on the U.S. mainland, as it carves a northerly arc off the East Coast later this week.
Earl, with sustained winds of 135 mph, was expected to turn northwest today, according to the latest update from the National Hurricane Center in Miami.
Category 4 is the second most powerful rating on the Saffir-Simpson scale and packs an enormously destructive punch if it makes landfall, including heavy damage to buildings, trees and power lines.
Some forecasters are predicting that the storm could eventually swing to within a few hundred miles of the U.S. Atlantic Coast, kicking up a powerful surf.
"The track of Earl has been trending west for a couple of days now," wrote Allan Huffman, a meteorologist and weather consultant in Raleigh, N.C. "Although there is some variation in the model guidance, I think that Earl will turn north around longitude 73-74W, and then turn northeast around 35N."
That would bring it within "a couple hundred miles of the North Carolina Outer Banks and Cape Cod," he added. "Obviously any slight shift west would be big."
Should Earl get that close to the coast late Thursday or early Friday, it is likely to close airports and sea lanes, wreaking havoc with commercial and passenger travel while ground transportation would likely be affected far inland by heavy rains.
On Monday, swimmers at the family resort of Ocean City, N.J., were told not to go into the water beyond waist-deep as violent waves kicked up by Danielle pounded the beach. Danielle was downgraded Monday from a hurricane to a tropical storm.
A guard rode a WaveRunner parallel to the beach to make sure swimmers weren't going too far out, and the beachside guards were not shy with their whistles.
Over the weekend, lifeguards in shore communities in New Jersey pulled out scores of struggling swimmers. Surf schools scrapped their lessons, and boogie boards were barred.
Tropical Storm Fiona formed in the Central Atlantic on Monday afternoon, and was forecast to follow a path similar to Earl's, parallel to the U.S. coastline. It was not projected to strengthen into a hurricane over the next five days.
