Millions along the East Coast breathed a little easier Friday after forecasters said Hurricane Joaquin would probably veer out to sea. But a freakishly powerful rainstorm fueled in part by the hurricane threatened to bring ruinous flooding to parts of the Atlantic Seaboard over the weekend.

With the soil already soggy and roads swamped in places from days of rain, East Coast states braced for what forecasters said could be unprecedented and life-threatening downpours over the next few days.

Maryland, New Jersey, North Carolina, South Carolina, Virginia and parts of Delaware were under states of emergency, though meteorologists said the Carolinas will probably get the worst of it, with 15 inches of rain in some places and landslides possible in the mountains.

"It's going to be enormous," meteorologist Ryan Maue of Weather Bell Analytics said. "It's going to be a slow-motion disaster."... Read More: Yahoo News