Rain that washed out ballgames and festivals in southern Florida was moving north and expected to meet cold air moving south from Canada, forecasters said.
Tornado watches were issued late Saturday in central and southern Florida.
Severe thunderstorms with wind gusts up to 34 mph struck Delaware, New Jersey and eastern Pennsylvania on Saturday night.
Up to 4 inches of rain was forecast Sunday from Washington, D.C., to New York City.
“It’s going to be a very, very intense Nor’easter,” said Michael Eckert, senior branch forecaster with the National Weather Service based in Camp Springs, Maryland.
Winds of 30 to 50 miles per hour are expected on the coast.
“The weather will be going downhill during the day on Sunday,” Eckert said.
Snow is forecast to fall across the Appalachians in West Virginia and reach central Pennsylvania on Sunday night and move up to the Buffalo, N.Y., area by Monday. Snow levels are forecast to be above 1,000 feet elevation by Monday night. Snow was also possible for Buffalo and Pittsburgh.
The Weather Channel warned this would be heavy, wet snow that could cause tree and power line damage, especially after record March warmth sent trees into full leaf far earlier than usual.
Heavy rainfall capable of flooding was also expected Sunday into Monday morning in southern New England and eastern Maine and New Hampshire later Monday.
NASA said Monday's planned arrival of the shuttle has been postponed "until further notice."
The Enterprise is being brought to the city where it has a new permanent home waiting at the Intrepid Sea, Air and Space Museum.
NASA managers are monitoring weather forecasts and will reschedule the shuttle's flight as soon as possible, the space agency said.
The plan is to fly the shuttle atop a carrier aircraft to New York's John F. Kennedy International Airport. It will be moved by barge to the Intrepid museum for public display.
The museum is at a decommissioned aircraft carrier moored at Manhattan. It's been making room for the shuttle on its flight deck.