A boy takes cover from a wave caused by the approaching of Hurricane Earl on Monday in Fajardo, Puerto Rico. Earl battered some islands across the northeastern Caribbean with heavy rain and winds Monday, rapidly intensifying into a major storm that could pose a threat to the East Coast of the United States.

San Juan, Puerto Rico ? Hurricane Earl battered tiny islands across the northeastern Caribbean with heavy rain and roof-ripping winds Monday as it rapidly intensified into a major Category 4 storm taking a path projected to menace the United States.

Already dangerous with sustained winds of 135 mph, Earl was expected to gain more strength before potentially brushing the U.S. East Coast this week and bringing deadly rip currents.

The U.S. National Hurricane Center in Miami warned coastal residents from North Carolina to Maine to watch the storm closely.

“Any small shift in the track could dramatically alter whether it makes landfall or whether it remains over the open ocean,” said Wallace Hogsett, a meteorologist at the center. “I can’t urge enough to just stay tuned.”

In the Caribbean, Earl caused flooding in low-lying areas and damaged homes on islands including Antigua and Barbuda, Anguilla and St. Maarten. Several countries and territories reported power outages. Cruise ships were diverted and flights canceled across the region.

The storm’s center passed just north of the British Virgin Islands on Monday afternoon. By nighttime, the hurricane was pulling away from the Caribbean, but heavy downpours still threatened to cause flash floods and mudslides in Puerto Rico and the Virgin Islands by drenching already saturated ground.

Earl was forecast to approach the U.S. Mid-Atlantic region around Thursday, before curving back out to sea, potentially swiping New England or far-eastern Canada.

The Hurricane Center said it was too early to say what effect Earl would have in the U.S., but warned it could at least kick up dangerous rip currents. A surfer died in Florida and a Maryland swimmer had been missing since Saturday in waves spawned by former Hurricane Danielle, which weakened to a tropical storm Monday far out in the north Atlantic.