How much harm could Hurricane Irene do? It depends largely, of course, on the storm's winds and rain where it makes landfall, but emergency managers warn that the tides could make a tremendous difference as well.
There is a new moon on Sunday evening -- and the storm track, as currently forecast by NOAA, will take Irene on Sunday over the major population centers around Washington, Baltimore, Philadelphia, New York City and into New England. A new moon means tides, shifting rhythmically, could be especially high during the daytime this weekend as the moon with its gravity passes overhead.
That could add to the 10-foot predicted storm surge -- the bulge of water a storm pushes out of its way as it churns over open ocean.
"An extremely dangerous storm surge will raise water levels by as much as seven to 11 feet above normal tide levels over the Bahamas," said the National Hurricane Center in a morning advisory. "Near the coast, the surge will be accompanied by large and dangerous waves."
Historically, NOAA warns, people do not die in hurricanes as they hit; instead, the most deaths happen when people come out after the storm has passed and try to make their way through floodwaters.
Dare County, N.C., which includes the Outer Banks, has ordered a total evacuation starting at 8 a.m. Friday. Visitors to the area -- and this is peak vacation time -- were already told to leave starting this morning. All told, 180,000 people there are being ordered to move inland.
County officials, according to ABC News' Matt Gutman, said they were "extremely concerned, telling us that on its current track, Irene is a bigger threat than any other storm in memory."
Virginia's Gov. Bob McDonnell declared a state of emergency as a "precautionary measure," making it easier to get emergency personnel into position. Other states from South Carolina to New England did the same.
"It is imperative that, in an abundance of caution, all Virginians, state agencies and localities prepare for this storm," McDonnell said.
And officials in the Northeast got ready too. The center line of the hurricane center's projected path takes the storm right over New York City on Sunday, though that could change as it comes closer.
"By the time Irene gets to us, which it is forecast to do sometime on Sunday, it certainly will still be a powerful storm," said New York's Mayor Michael Bloomberg today, "but anything can happen in terms of its direction and its severity."
He urged people to check whether they live in hurricane evacuation zones (New Yorkers can click HERE to find out). And he suggested people stock up on supplies and make a "Go Bag," with drinking water, a first-aid kit, flashlight, medications and other essentials if they must leave on short notice.