Both coasts are expected to be hit by wet and windy weather just in time for the busiest travel days of the holidays.
Heavy rains and wind gusts up to 60 mph were expected from Northern California to Washington state Wednesday night and into Thursday.
On the East Coast, central and south Florida were anticipating heavy winds, hail and possible tornadoes, forecasters said.
The National Weather Service said moisture from the Gulf of Mexico and the Atlantic Ocean were expected to create heavy rainfall of 1 to 2 inches across the Southeast and the Appalachians eastward, with as much as 3 inches along the Florida peninsula and in eastern North Carolina and southern New England.
By Thursday night, the storm will start affecting the Northeast, according to the National Weather Service.
The travel hubs of Washington, D.C., New York and Boston all could see up to 4 inches of rain and possible flooding from Thursday night to Friday night. Surrounding areas will see higher-than-average temperatures, but in New York, wind gusts could reach 35 mph.
Before the forecast, holiday travelers were warned that traffic could multiply their travel time by four. A record 112.5 million Americans are expected to take to the roads, skies and rails this holiday weekend, starting Wednesday, according to AAA.
"With a record-level number of travelers hitting the road this holiday, drivers must be prepared for delays in major metro areas — with Thursday, Dec. 20, being the nation's worst day to travel,” said Trevor Reed, a transportation analyst at INRIX, a travel data company.
Local forecasters in New York and New England predicted possible snow flurries on Christmas Eve but said they expected Christmas Day to be dry.