“Confidence in the details of the track forecast late in the period remains low, since the environmental steering currents are complex and the model guidance is inconsistent,” Beven said. “It is therefore way too soon to talk about specific wind, rain, or surge impacts from Joaquin in the U.S.”

U.S. coastline

There is a 30 percent chance that tropical storm-strength winds will reach the coastline from North Carolina to Delaware in the next five days and a more than 10 percent chance the storm-strengthwinds of 39 mph or more will strike anywhere from Massachusetts to South Carolina in the same time frame.

Some models suggest the storm will hit somewhere in North Carolina in four days, while the European Centre for Medium- Range Weather Forecasts model takes it off to the northeast toward Bermuda, said Phil Klotzbach, lead author of the Colorado State University seasonal hurricane forecast.

‘Tough call’

“Since the ECMWF is generally considered to be the best track model, it’s a really tough call,” Klotzbach said. “I’ll be curious to see what the updated model guidance shows in a couple of hours.”

The other problem facing forecasters is that the storm’s forward speed will probably increase should it become a threat to the U.S., resulting in “impacts along the coast occurring sooner than currently forecast,” Beven said. If that happens, “a hurricane watch could be required for portions of the U.S. coast as early as Thursday evening,” he said.

The current forecast shows Joaquin’s top winds reaching 115 mph by Saturday, which would make it a Category 3 storm, or major hurricane, on the five-step Saffir-Simpson scale.

The U.S. hasn’t been hit by a major hurricane since 2005.

Even without a strike by Joaquin, the U.S. East Coast has been drenched by heavy downpours. More than 10 inches of rain is forecast to fall throughout parts of southern New Jersey, Delaware, Maryland, Virginia and North Carolina in the next seven days, according to the U.S. Weather Prediction Center in College Park, Maryland.

Flood watch

Flood warnings and watches currently cover most of New England and much of New York, the National Weather Service said.

As of noon New York time, 78 flights in the U.S. were cancelled and 794 more delayed, according to FlightAware, a Houston-based airline tracking service.

In the Central Bahamas, Joaquin, the 10th storm of the six- month Atlantic hurricane season, could drop as much as 5 inches (13 centimeters) of rain. Rum Cay and San Salvador may get 10. In addition, Joaquin’s storm surge is expected to raise water levels 2 to 4 feet above normal. The surge “will be accompanied by large and dangerous waves,” the advisory said.

Cat Island, the Exumas, Long Island, Rum Cay and San Salvador can expect hurricane-force winds within the next 36 hours. The storm may later hit the northwestern Bahamas, including Abacos, Berry Islands, Bimini, Eleuthera, Grand Bahama Island and New Providence.

--With assistance from Ladka Bauerova in Prague.

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