Hurricane Omar weakened rapidly as it surged into the Atlantic on Thursday, after threading its way through the small islands of the northeastern Caribbean as a fiercely powerful storm that ended up causing relatively little damage, U.S. forecasters said.

The 15th tropical cyclone of a busy Atlantic hurricane season sank boats in harbors and knocked down trees and utility poles on Caribbean islands, according to reports from residents throughout the vulnerable area.

It posed no threat to the United States or any other land area as it raced out over the open waters of the Atlantic.

"It missed all the major land masses. The only land mass that we know it hit was an itsy-bitsy island called Sombrero and that's uninhabited," said senior hurricane specialist Stacy Stewart at the U.S. National Hurricane Center.

"If it was going to go on a track that wouldn't affect anybody or at least not affect anybody significantly, then it absolutely took that track," Stewart said.

Omar formed north of the Dutch island of Curacao on Tuesday, briefly disrupting oil operations in Venezuela and shutting down processing units at a refinery in the U.S. Virgin Islands.

It strengthened as it powered toward the Virgin Islands into a fierce Category 3 storm on the five-step Saffir-Simpson scale of hurricane intensity, and neared the threshold of Category 4 at its peak in the Anegada passage between the Dutch-French island of St. Maarten and the Virgin Islands.

By 11 a.m. EDT (1500 GMT), the storm's top sustained winds had dropped to near 85 miles per hour (140 km per hour), however, making it a minimal Category 1 hurricane, the Miami-based center said.

BOATS SUNK

Omar sank at least four boats at the Christiansted harbor in St. Croix in the U.S. Virgin Islands and toppled trees and power lines across St. Maarten.

In the Maho Bay area of St. Maarten, the storm mowed down a row of wooden nightclubs that were popular with visitors, said Paul Boonstra, a Dutchman who runs boat tours.

A hotel receptionist in Road Town on Tortola in the British Virgin Islands said the storm's passage had been largely uneventful.

The only land area to really feel strong storm conditions was the eastern end of St. Croix, but sustained winds there did not exceed tropical storm force, the hurricane center said.

In the U.S. territory of Puerto Rico, home to about 4 million people, Omar passed too far off the eastern coast to cause more than flooding along a handful of small roads.

"This was another bullet we were able to dodge," said Rafael Mojica, of Puerto Rico's National Weather Service.

Processing units at the 500,000 barrel-per-day Hovensa refinery on St. Croix in the U.S. Virgin Islands were shut down ahead of Omar's arrival and the operators were conducting an assessment on Thursday before restarting it, Hess Corp said.

Hovensa is a large supplier of gasoline and heating oil to U.S. East Coast markets.

The 2008 hurricane season, which officially ends on Nov. 30, has far more active than average.

Of the most serious storms so far, Hurricane Gustav hit near New Orleans, the city devastated by Hurricane Katrina in 2005, and Hurricane Ike struck Houston. Both threatened oil rigs off the U.S. Gulf Coast.

In Haiti, more than 800 people were killed in flooding caused by Fay, Gustav, Hanna and Ike, while Cuba suffered $5 billion in damage after Gustav and Ike tore through it.