The Atlantic storm Earl has become the second major hurricane of the season, and it is expected to continue gaining strength as it heads toward the northern Virgin Islands.

Earl is currently a Category 3 storm with maximum sustained winds of 120 miles per hour. The National Hurricane Center (NHC) said low wind shear and warm water ahead of Earl "appears conducive for additional strengthening during the next few days."

Its future threat to the U.S. East Coast is still unknown, the NHC said, noting, "This is a good time to remind everyone that NHC average track forecast errors are 200 to 300 miles at days four and five. Given this uncertainty, it is too soon to determine what portion of the U.S. East Coast might see direct impacts from Earl."

As for areas currently under threat, the NHC said the storm is moving west-northwest at around 15 miles per hour, and on the forecast track "the center of Earl will pass near or over the northernmost Virgin Islands this afternoon and this evening."

A hurricane warning is in effect for Anguilla, Saint Martin and Saint Barthelemy; St. Maarten, Saba and St. Eustatius of the Netherlands Antilles; the British Virgin Islands; the U.S. Virgin Islands; and the Puerto Rican islands of Culebra and Vieques.

For locations within the hurricane warning area, the NHC said hurricane conditions are expected within 12 hours of its 11:00 EDT update. "Preparations to protect life and property should have already been completed," the NHC said.

A hurricane watch is in effect for Puerto Rico, the NHC said, and a tropical storm warning has been issued for Antigua, Barbuda, Montserrat, St. Kitts and Nevis.

Hazards to land include hurricane-force winds, storm surge that will raise water levels by as much as three-to-five feet above ground level within the hurricane warning area, and rainfall of four-to-eight inches with possible isolated maximum amounts of 12 inches.

According to catastrophe modeler AIR Worldwide, the dominant construction type for homes in the northernmost Leeward Islands is masonry and a mix of masonry and reinforced concrete for commercial structures. AIR said it expects minor damage to well-constructed residential buildings and engineered structures, while poorly constructed homes and light metal structures such as warehouses could suffer significant damage.

Beyond today, risk modeler Risk Management Solutions (RMS) said "the NHC forecast track will take Earl north, with the extended forecast showing the system to pass between the U.S. East Coast and Bermuda" sometime between Thursday and Friday. If the storm follows that track, the U.S. East Coast and Bermuda would be spared, RMS said, but an impact along the coast--particularly North Carolina--or on Bermuda is within the "large cone of uncertainty" associated with the forecast.

Elsewhere in the Atlantic, about 1,050 miles east of the Lesser Antilles, the NHC said another system moving westward at about 20 miles per hour has a 90 percent chance of forming into a tropical cyclone during the next 48 hours. The NHC said if current trends with the system continue, it could become a tropical depression later today or tonight.

Meanwhile, Hurricane Danielle, which late last week became the first major hurricane of the season, has weakened in the Atlantic to a Category 1 storm. It is expected to lose its tropical characteristics later today, the NHC said, but will remain a "large and powerful cyclone over the far north Atlantic for the next two days."