The statue at the Martin Luther King Jr memorial by the Tidal Basin in Washington, D.C. in August 2011. (Marvin Joseph)

Tens of thousands of people, including President Obama, are expected at the gala memorial dedication ceremony on the Mall at 11 a.m. Sunday, when current forecasts have the storm centered over the Eastern shore. But the expected track of the storm, which was centered north of Haiti Tuesday morning, has moved to the east several times in the last few days, and experts say forecasts five days in advance are often tentative.

Park Service spokesman Bill Line said the government is eyeing Irene and “considering alternatives” to Sunday’s dedication. Many of the 30,000 chairs for Sunday’s ceremony already have been set up in a field west of the memorial on Independence Avenue SW, and a large stage with tall scaffolding was being erected Monday.

The storm also threatens to affect late August vacationers at beaches up and down the East Coast, from the Outer Banks of North Carolina to New England.