* Earl seen becoming powerful hurricane
* Hurricane warnings across the Caribbean
* U.S. East Coast could feel effects later in week
MIAMI, Aug 30 (Reuters) - Hurricane Earl strengthened as it began buffeting the Northern Leeward islands in the Caribbean on Monday and was seen becoming a powerful storm within the next 24 hours, the U.S. National Hurricane Center said.
Earl carried sustained winds of 105 miles per hour (169 kph) and was a Category 2 hurricane in the five-step Saffir-Simpson scale of intensity.
"Hurricane conditions are now spreading into the Northern Leeward Islands and will spread westward into the Virgin Islands later today," the hurricane center said in its 5 a.m. (0900 GMT) advisory.
"Earl is expected to become a major hurricane by tonight or early Tuesday," it added.
The storm's center was 50 miles (80 km) east-northeast of the French overseas island of St. Martin and moving north-northwest.
Hurricane warnings were in effect through the Caribbean, including the U.S. and British Virgin Islands, Antigua and Barbuda and the British overseas territories of Montserrat and Anguilla.
Tropical storm conditions were expected to spread over the U.S. territory of Puerto Rico on Monday, with hurricane conditions possible by evening.
The hurricane center warned of a storm surge, dangerous waves and heavy rains that could cause flash flooding and mudslides in areas of higher elevation.
Caribbean airline LIAT canceled 41 flights to several destinations in the eastern Caribbean and shut down its reservation service because of Earl's approach, according to a company statement.
Forecasters said Earl could affect the U.S. East Coast later this week.
"It looks like the storm will be east of the Bahamas on Wednesday, east of Cape Hatteras on Thursday and then probably east of or near Cape Cod and Long Island on Friday," Miami's WFOR-TV forecaster Jeff Berardelli said on CBS radio.
In the North Atlantic, Hurricane Danielle, a major Category 4 storm last week, was barely a hurricane on Monday morning as its sustained winds fell to 75 mph (121 kph). The storm was expected to lose its tropical characteristics later in the day.
It was about 440 miles (708 km) south of Newfoundland. (Reporting by Michael Connor; Additional reporting by Linda Hutchinson in Port of Spain, Peter Cooney in Washington and Sam Strangeways in Bermuda; Writing by Peter Cooney; Editing by Jon Hemming)
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