Humberto is forecast to continue strengthening and is expected to be a Category 4 storm over the weekend. Predictions on how Humberto could affect Florida and the U.S. are difficult due to the Fujiwhara effect.

Hurricane Humberto has intensified into a Category 4 storm with 145 mph winds in the Atlantic. While no US landfall is forecast, dangerous swells and rip currents are affecting Puerto Rico, Bermuda, and the U.

Residents of the Carolinas, seldom fans of hurricanes, much less those reaching Category 5, are hopeful for a rhythm between Humberto and Imelda. Category 4 Hurricane Humberto, about 365 miles north-northeast of the Northern Leeward Islands at 11 a.

The storm in the Atlantic is forecast to stay out to sea. Another disturbance that could affect the U.S. was upgraded to Tropical Depression Nine.

That's an unlikely outcome, said CBS News meteorologist Nikki Nolan. But if such a collision does occur, it could produce what's called the Fujiwhara effect, a rare phenomenon in which two different storms merge and become entangled around a newly formed, common center.

A hurricane warning was in effect for the volcanic archipelago which could experience dangerous conditions from Gabrielle as early as Thursday.

At 5 p.m. Friday, the National Hurricane Center issued an advisory stating that Category 3 Hurricane Humberto is in the Atlantic Ocean, 430 miles northeast of the Northern Leeward Islands. The hurricane, with maximum sustained winds of 115 mph, is moving west-northwest at 5 mph.

Effects from Hurricane Humberto and Invest 94L on the US remain difficult to predict, but risks along the coast between Florida and NC are rising.