Powerful storm to lash East Coast with wind-swept rain this weekend

A significant storm is expected to charge up the Eastern Seaboard this weekend and Monday, generating strong winds, heavy rain and the potential for flooding. The track could take the system directly up Interstate 95, bringing the storm over most of the East Coast’s major cities and spelling widespread travel delays — especially Sunday into Monday.

Weather models remain divided on the specific track of the storm, but virtually all agree on one thing: The storm — which will organize in the eastern Gulf of Mexico on Saturday — will be unusually strong.

A storm of this strength in December would ordinarily dump a swath of heavy snow, but there’s hardly any cold air to be found in the eastern United States. That means the storm will be primarily wet, rather than white. Flooding is a distinct concern, however, especially along Florida’s Gulf Coast, where more than 4 inches of rain are possible.

The unusually mild air mass will support the potential for severe weather, including the risk of a few tornadoes. That threat could arrive late Saturday in Florida, and then could creep north into coastal Georgia, the Carolinas and even Virginia on Sunday depending on the storm track.

It will mark the second straight stormy Sunday-Monday along the East Coast. Earlier this week, another powerful storm system drenched much of the Mid-Atlantic and Northeast.

■ Heavy rainfall: The moisture-loaded storm system is forecast to drop 1 to 3 inches of rain from Florida to Maine; exactly where the heaviest amounts occur will depend on the storm track. Parts of northern Florida and central Georgia could receive 3 to 4 inches.

In Florida and the Southeast, much of the rain is expected Saturday night and Sunday. The rain should reach the Mid-Atlantic on Sunday into Sunday night, and the Northeast on Sunday night and Monday.

It could cause pockets of flooding, particularly in areas hit hard by the storm earlier this week where the ground is still saturated, including the zone from eastern North Carolina into the Delmarva and portions of Connecticut and Rhode Island.

■ Coastal flooding: No matter what track the storm takes, it will be preceded by onshore winds. That’s because lows in the Northern Hemisphere spin counterclockwise, so winds from the east are found on the north side of storm systems. Significant beach erosion and some pockets of at least moderate coastal flooding are probable. The European model forecasts 50-foot waves just a few miles offshore of the Outer Banks on Sunday night. Similar wave heights will be present offshore of Cape Cod on Monday.

■ Strong winds: The storm will be preceded by high pressure and tranquil weather. The contrast between departing high pressure and the arrival of an intense low pressure system will lead to stronger winds.

Weather models indicate the potential for 50- to 60-mph wind gusts for essentially the entire coastline from North Carolina to Downeast Maine, with 40- to 50-mph gusts inland. How far inland the strong winds reach will depend on the exact track of the storm. Slightly lesser winds, but still in the range of tropical-storm force, are probable for Florida and the shores of South Carolina.

■ Severe thunderstorms: There will be at least some potential for tornado activity in Florida on Saturday night. That’s because southerly winds east of the low-pressure system forming over the Gulf of Mexico will pump north a filament of warm, humid air. Meteorologists call this the “warm sector.”

Thunderstorms that sprout in the warm sector could rotate, though, because of changing winds with height. That will support at least some tornado risk.

“A low confidence forecast exists for Saturday evening/ night, but nocturnal tornado potential remains apparent across the Florida Peninsula,” writes the National Weather Service Storm Prediction Center.

There’s a chance the warm sector spreads as far north as the Carolinas or southeast Virginia late Sunday, but that depends on the storm’s track, which remains uncertain.

The storm is predicted to form Saturday in the Gulf of Mexico. There’s a broad, diffuse area of low pressure there now. An approaching upper-air disturbance over New Mexico will encourage a more concentrated area of low pressure to form and intensify.

A second upper-air disturbance — a pocket of high-altitude cold air, low pressure and spin - will swing out of the northwest, further strengthening the storm while tugging it westward.

It will probably continue to intensify until Sunday evening, by which point it will be somewhere between the Appalachians and coastal Carolinas. It will remain strong as it progresses northward, drenching New England to start next week before exiting into Atlantic Canada by Tuesday.