A powerful tropical depression blowing through the Caribbean looks set to become a hurricane that could threaten the US’ southern coast — amplifying fears it could combine with another hurricane already raging in the Atlantic to form a devastating superstorm.

Tropical Storm Imelda formed Sunday, and is expected to grow into a hurricane by Monday night or Tuesday morning, according to Fox Weather.

Forecasts expect Imelda to veer east and head out to sea without making landfall in the US by Wednesday – but that trajectory could place it on a collision course with Hurricane Humberto, which is currently spinning as a Category 4 storm over the Sargasso Sea region south of Bermuda.

Though forecasts say the storms won’t make a direct collision – Fox Weather Meteorologist Greg Diamond said the storms “will 100% not collide” – if they come within a few hundred miles of each other there is still a chance they could combine in a rare phenomenon known as the “Fujiwhara Effect.”

If that happened, Humberto and Imelda could spin around each other and eventually combine into one giant storm – and they would only need to come within 900 miles of each other for that scenario to be a possibility.

Exactly what would happen afterwards is difficult to predict without seeing real time data, but the new superstorm could exacerbate the already life-threatening effects Imelda is forecast to throw at the southern states even without making landfall.

Imelda is currently blowing over the Bahamas at about 35 mph on a northward trajectory that’s expected to hug Florida’s Atlantic coast and bring tropical force weather throughout the southern eastern seaboard on Monday.

Humberto, meanwhile, was elevated to a Category 5 hurricane over the weekend before weakening to a Category 4 Sunday, and was blowing north of the Dominican Republic on a northwestern trajectory.

And though neither storm is expected to make landfall in the US, the central Florida coast up through the Carolinas could face flooding from heavy rain, and storms wells up to two feet, some forecasts say.

Florida can expect tropical storm gusts of 40 mph from West Palm Beach to Jacksonville from Imelda, Fox Weather said, with rains between one and three inches falling through Tuesday morning.

And Georgia and the Carolinas can expect to see up to five inches of rain in the coastal regions, especially around Myrtle Beach and Wilmington, Fox Weather said.

North and South Carolina have already declared states of emergency to prepare for dangerous effects the weather could throw at the coasts.

“What we learn every time is we never know where they are going to go,” North Carolina Gov. Josh Stein said at a press conference about the declaration.

“This storm is deadly serious. Not just serious. Deadly serious,” he added.

And while the landfall is not expected from Imelda, the National Hurricane Center cautioned it’s never out of the question.

 “There are still scenarios where the system could come in and make landfall or sit here for several days or stall out and then move off to the east,” National Hurricane Center Deputy Director Michael Brennan told Fox Weather.

“It’s not going to [need] a direct landfall for there to be some significant impacts from storm surge, winds, rainfall, flooding, especially if we have a system that’s meandering here along or near the coast, say, of South Carolina.”