A significant fall storm may form along the East Coast late this week as a cold front combines with the remnants of Category 5 Hurricane Willa, forecast to hit Mexico’s west coast Tuesday. The storm may generate heavy rain, mountain snow, and, at the coast, strong winds and high seas.

The biggest risk of disruptive weather will be in the Mid-Atlantic and Northeast over the weekend. It is too soon to project exactly how this storm will unfold and where it will hit hardest. There is also the chance it is steered more out to sea, minimizing the effects.

The storm threat is still five to six days away, but computer models have shown a pattern favorable for East Coast storms in late October for more than a week.

Like all East Coast storms, the exact track will determine where the heaviest precipitation occurs and what locations, if any, might see snow. There is also uncertainty in the storm’s strength, which will have big implications for how much precipitation falls and what type and whether strong winds and flooding become a threat along the coast.

But models suggest this storm has the potential to be formidable. It will develop as the remnants of Willa, presently situated in the eastern tropical Pacific Ocean near Mexico’s west coast, are drawn northeast from Mexico into the Gulf of Mexico midweek. A new storm system will form along an old stalled-out front and track from the northern Gulf Coast through the Southeast on Thursday and Friday.

Willa’s remnants — as they enter the Gulf of Mexico — will not bear any similarity to the monster storm in its current state and will be much weaker. Over the Gulf of Mexico, it is not out of the question that the remnant circulation attempts to regenerate into a tropical entity, but models do not presently predict this.

Willa’s remnants are first likely to produce substantial rainfall over Central Texas, which has recently endured severe flooding, on Wednesday. The rain is then likely to spread on Thursday and Friday over some of the areas hit by Hurricane Michael, including the Florida Panhandle and Georgia.

As the storm system develops and tracks along the northern Gulf Coast toward the Mid-Atlantic and Northeast, models project rainfall totals of about one to four inches. This may be enough to cause pockets of flooding, especially in areas that have had substantial rain in recent weeks, but widespread issues are less likely. The storm system will be moving along fast enough to prevent a more serious flood threat.

The storm system is not expected to gain significant strength until it reaches the East Coast on Friday or Friday night, when it begins to interact with a cold front.

The timing and location of this merger will have significant implications for the storm track and how big a deal this storm becomes along the East Coast. If the merger occurs earlier and closer to the coast, the storm is more likely to come right up the coast with significant rain, snow and wind. But if it occurs later and farther offshore, it may mean more of a glancing blow.

Of the European modeling system’s 51 simulations (see below), about half keep the storm close to the Mid-Atlantic and Northeast coast, and the other half take it more out to sea.

The American modeling system, not shown, shows a similar range of possibilities as the European one but slightly leans more toward an out-to-sea solution.

If the storm hugs the coast and becomes a powerhouse, widespread rainfall totals along the Interstate 95 corridor could reach one to three inches. And it would probably draw down cold air.

The primary (operational) simulation of the European model is forecasting highs of only 40 to 45 degrees in Washington and Baltimore on Saturday, when substantial rain is possible. In this scenario, elevations above 2,000 feet in the Appalachians could see accumulating snow. Gale-force winds and heavy surf will probably batter the coast, resulting in some erosion and coastal flooding.

Farther north, into New England, the storm’s effects would probably hit Sunday, and the availability of colder air could even allow some snow to occur at lower elevations away from the coast.

But again, there is a wide range of possibilities with respect to how this storm ultimately evolves, and it is too soon to nail down specifics.

Irrespective of exactly how this storm develops and tracks, unseasonably chilly air is likely to follow in its wake Sunday into early next week throughout the Mid-Atlantic and Northeast.