Forecasters expect Tropical Storm Florence to become a "major hurricane" Monday as it continues to approach the southeastern U.S. East Coast.

In its 5 a.m. EDT advisory, the National Hurricane Center said "a rapid phase of intensification" is expected to begin by Sunday night as Florence officially becomes a hurricane.

Florence is expected to travel between Bermuda and the Bahamas on Tuesday and Wednesday before approaching the southeastern U.S. coast on Thursday.

The Miami-based weather center says Florence's maximum sustained winds are estimated to be 70 mph. The storm is centered about 765 miles southeast of Bermuda and moving west at 6 mph (9 kph).

The NHC notes that "given the uncertainty in track and intensity forecasts" its too soon to determine the impact the storm could have on the East coast, but "the risk of direct impacts continues to increase."