Tropical Storm Humberto has formed in the Atlantic, and forecasters anticipate it will intensify into a major hurricane, posing a threat to millions along the East Coast in the coming days.

The rapidly growing storm developed overnight, moving from an unnamed tropical wave to a tropical depression to a named storm within a few hours.

Presently, it is moving across the Atlantic, several hundred miles away from the Leeward Islands of the Caribbean, which include Antigua, St Kitts, and the British and US Virgin Islands, and currently boasts sustained winds of 45 mph.

The National Hurricane Center (NHC) forecasts that Humberto will develop into a Category 3 hurricane by early Monday morning, with winds increasing to over 110 mph.

By Tuesday, hurricane forecasters warn that Humberto’s course will take it dangerously close to the mid-Atlantic states, including South Carolina, North Carolina, and Virginia.

A Category 3 hurricane near the US could have a powerful impact on coastal communities, bringing several hazards, including rough surf and potentially deadly rip currents for beachgoers.

However, its impact on the East Coast may end up being completely unpredictable next week, as meteorologists fear Humberto could soon merge with another brewing storm system approaching Florida.

Hurricane trackers warned Thursday morning that a potential storm system, dubbed Invest 94L, is likely to burst into tropical storm status this weekend and make landfall in the Southeast shortly after.

Early spaghetti models for Invest 94L, which could become ‘Imelda’ if it strengthens into a tropical storm, already project a direct hit in Georgia or the Carolinas.

A spaghetti model shows the different possible paths a tropical storm or hurricane might take, based on predictions from multiple weather computer programs. 

Each line represents one model’s guess about where the storm could go. If the lines are close together, it means most models agree on the path, and the prediction is more certain.

Currently, 94L is forming right over the Dominican Republic. It’s still just a tropical wave, a disorganized system of showers, thunderstorms, and gusty winds, but NHC has given it a 90 percent chance of becoming a dangerous tropical cyclone within seven days.

While a direct hit on the Southeast would be life-threatening on its own, meteorologists believe there’s a chance ‘Imelda’ and Humberto merge in a historic weather phenomenon called the Fujiwhara Effect.

It typically takes place when two tropical cyclones (hurricanes or tropical storms) get within 900 miles of each other, close enough for them to start ‘feeling’ each other’s presence in the ocean.

Current tracks have revealed that ‘Imelda’ could form right as Humberto is approaching the East Coast, setting the stage for the Fujiwhara Effect to create one massive hurricane or spin both storms in unpredictable directions.

These events are rare during the Atlantic hurricane season, with only four instances being reported near the East Coast since 1995.

WESH 2 chief meteorologist Tony Mainolfi explained that the Fujiwhara Effect generally makes one of three things happen when two major storms start interacting.

The storms might rotate around a common point between them, like two hurricanes doing a slow dance, spinning around each other in unison. 

In some cases, a stronger storm might absorb a weaker one, creating an even more massive weather event than either storm would have been on their own.

If the two storms end up being similar in size and strength, however, they might repel each other and get thrown in completely different directions that forecasters won’t be able to project beforehand.

Dr Levi Cowan, creator of the spaghetti model website Tropical Tidbits, said that the two storms are only about 600 miles apart, making them prime candidates for a Fujiwhara Effect.

‘These two systems may develop as a pair. The problem with that is they may do a little dance with each other,’ Cowan said in a YouTube video on Wednesday.

Cowan, a meteorologist with a PhD in meteorology from Florida State University, noted that many of the current storm models predict that both Humberto and ‘Imelda’ will stay offshore and eventually move away from the East Coast.

However, the closer these storms get to each other could cause them to ‘slingshot’ into the coast, making long-term predictions for next week even more difficult.