By JENNIFER PRESTON

With the nation’s top weather officials saying there is now a 90 percent chance that Hurricane Sandy will slam into the East Coast early next week, emergency management officials from Virginia to Massachusetts outlined plans for what is being described as a monster of a storm.

Gov. Bob McDonnell of Virginia declared a state of emergency and advised residents in low-lying areas in the eastern part of the state to prepare to evacuate. Gov. Martin O’Malley of Maryland issued a similar order for all counties in his state and activated the National Guard to assist in emergencies.

“As Hurricane Sandy makes its way north, I urge all Maryland residents to prepare for extreme weather,” Mr. O’Malley said. “I urge all Marylanders to review their family emergency plans, make sure their emergency supplies like batteries and water are fully stocked and to stay informed.”

Washington is bracing for the worst, reports The Washington Post’s Capitol Weather Gang blog. The presidential candidates and campaign aides are expressing concern about the impact the storm is having on last-minute campaign plans and messages, my colleague Michael D. Shear reports. Mitt Romney’s campaign canceled a Virginia Beach rally that the campaign had scheduled for Sunday evening.

As my colleagues, Timothy Williams and John Schwartz report, the storm is expected to come ashore early Tuesday, somewhere between Virginia and southern New England, with landfall most likely in the Delmarva Peninsula or southern New Jersey. Hurricane Sandy is then on track to head toward southeastern and central Pennsylvania before moving north into upstate New York, the latest analysis from the National Hurricane Center shows.

But Dr. Louis Uccellini, director of NOAA’s National Centers for Environmental Prediction, said the storm’s track could shift 200 miles in either direction. This could put New York City directly in its path, and as our colleagues on City Room report, it could force the shutdown of the city’s subway system. Mayor Michael R. Bloomberg warned that people in low-lying areas need to be prepared to evacuate.

What is certain, Dr. Uccellini said during a briefing with reporters on Thursday, is that this is large storm, a collision of a tropical storm moving west instead of east at the same time a winter storm is moving in from the Midwest during a full moon. “We are dealing with categories here that we don’t normally see,” he said.

The full moon is adding to growing concern about the size of the surge along the coast.

The storm is expected to cut across a large swath of mid-Atlantic states and New England. Forecasters warn it is capable of producing sustained tropical-force winds, downing power lines and leaf-covered branches, up to 10 inches of rain, inland flooding, coastal surge and more than a foot of snow in the mountains of West Virginia and snowfalls as far west as Ohio.

On Friday, the storm, which left more than 30 people dead in the Caribbean, moved north away from the Bahamas. As it moved north, parallel to the East Coast, Florida felt its impact on Friday with strong winds and high waves but no reports of serious damage.

A tropical storm watch has been issued for most of the Carolina’s because tropical force winds onshore and offshore are expected as the storm moves north in the coming days before veering west.

Under the current tracking projection, the storm would move into Delaware and southern Pennsylvania before moving north. Delaware officials warned residents that power outages could last days. Classes were canceled at many schools on Monday and several hospitals and clinics postponed appointments and procedures that were not urgent. Along the state’s coastline, efforts were made to help protect its beaches.

Gov. Chris Christie of New Jersey, who skillfully used social media to remind people to get off the beaches during Hurricane Irene last year, took to Twitter on Friday to deliver updates about emergency preparation measures and precautions.

In Pennsylvania, Gov. Tom Corbett also issued an emergency declaration on Friday. The storm is expected to not only bring heavy rain, sustained high winds and power outages but snow in some areas of southwestern Pennsylvania. In this video, he talks about the state’s emergency preparations.

In Philadelphia, Mayor Michael A. Nutter and his emergency management officials urged residents to begin preparing as the forecast projected a “historic event” for Philadelphia and the region.