Hurrricane Irene

Steve Jessmore/The Sun News , via Associated Press

Chris Jaeger, a landscaping manager, prepared for the hurricane by filling his truck and 10 five-gallon gas containers in Garden City, S.C., on Tuesday.

“We are out of the cone at the moment, though we have seen it wobble in the past,” said Peter Elwell, the town manager in Palm Beach, Fla., referring to the constantly evolving cone on forecast maps that designates a hurricane’s probable path. “The cone moving away from us is a mixed bag: you know the bullet you are dodging is going to hit somebody else.”

The mouth of the dangerous storm’s cone took dead aim on Tuesday at North Carolina, where officials scrambled to get ready. But federal and state authorities warned residents in other places not to be complacent; they said the hurricane would probably affect nearly every state along the East Coast.

Forecasters at the National Hurricane Center here said they were becoming increasingly confident that Hurricane Irene, a Category 1 storm on the Saffir-Simpson wind scale late Tuesday with sustained winds of 90 miles per hour, would gradually increase in strength over the warm Gulf Stream waters. The Bahamas will bear the brunt of the storm over the next several days before it is expected to veer on a more northward path toward the Carolinas, forecasters said.

The huge hurricane would most likely make landfall in North Carolina by the weekend, they said.

“There is still a lot of uncertainty,” said Jorge Aguirre, a 17-year veteran meteorologist at the National Hurricane Center. “These things are often unpredictable. I would not say Florida is completely off the hook just yet. It’s going to be a very close call.”

Hurricane Irene, the first major storm of the Atlantic hurricane season, could threaten “the entire East Coast,” W. Craig Fugate, head of the Federal Emergency Management Agency, said Tuesday in a conference call with reporters.

The storm was nudged away from its 10-m.p.h. path toward Florida by weakness in a high pressure system parked over the southeastern United States, forecasters said. If that system changes, the hurricane could still graze Florida’s coastline, they said.

The last significant hurricane to strike Florida was the ferocious and highly destructive Wilma, in 2005.

Up and down the Eastern Seaboard on Tuesday, mayors, police chiefs and emergency preparedness personnel took no chances because the path of the hurricane could suddenly change. They made plans for the worst while hoping for the best.

“This is a dance we’ve done many times,” said Roy Rutland, a spokesman for the Miami-Dade Police Department. “If there is a police department prepared for hurricanes, it’s Miami-Dade. Even if this is just a tropical storm in our area, we have contingency plans in place to deal with it.”

No hurricane has made landfall in the United States since Hurricane Ike barreled into Texas in 2008. On the social media networks like Facebook and Twitter, there was great interest in tracking Hurricane Irene’s every gyration, at least until an odd 5.8-magnitude earthquake struck Mineral, Va., at 1:49 p.m. Tuesday, and was felt as far away as Toronto and Georgia.

Several officials said they were concerned about an unusual “double-whammy” hitting the Middle Atlantic States: an earthquake followed by a hurricane.

“Two in one week? Unlucky,” said Joseph P. Riley Jr., the mayor of Charleston, S.C., for 35 years. “If we have a Category 3 storm moving in our direction, it’s smart to take every precaution, even if the cone says it may not. We don’t look at it begrudgingly or as another headache. We see it as an opportunity. We know our citizens might need our help, and we want to do the best job possible.”

The National Hurricane Center’s tracking cone is based on a 250-mile range of error in forecasts of the direction of hurricanes over the last five years.

“There is something psychological about the cone,” said Bryan Koon, the director of the Florida Division of Emergency Management. “Once people are out of the cone, they tend to back off on their preparations. But it’s always better to be prepared.”

Timothy Williams contributed reporting from New York.