MIAMI — The U.S. East Coast could be hit with a powerful hurricane next week as Tropical Storm Florence continues to strengthen as it moves toward the mainland, forecasters said Saturday.

Florence is expected to become a major hurricane by Monday, the National Hurricane Center said, adding that “a significant phase of intensification” is expected late Saturday.

The Miami-based weather center said although the storm could intensify to a Category 4 hurricane by midweek, its path was still unclear.

“Florence is forecast to be a dangerous major hurricane near the southeast U.S. coast by late next week, and the risk of direct impacts continues to increase,” the hurricane center said Saturday.

Officials in the Carolinas warned residents to prepare and to brace for impact.

Pasquotank-Camden Emergency Management advised Saturday that the risk of storm impacts to the east coast next week have increased, though there's a lot of uncertainty still in the model forecasts. However, the agency urged people to take time this weekend to prepare their families and homes for a hurricane.

On Friday, North Carolina Gov. Roy Cooper declared a state of emergency and urged residents to use the weekend to prepare for the possibility of a natural disaster.

“We are entering the peak of hurricane season and we know well the unpredictability and power of these storms,” Cooper said.

Governors in both South Carolina and Virginia declared a state of emergency Saturday to give their states time to prepare for the possible arrival of the storm. South Carolina Gov. Henry McMaster emphasized that there’s no way to know yet when and where the storm will hit land, or when evacuations might be called.

The U.S. Navy is making preparations this weekend for its ships in the Hampton Roads area to leave port. The U.S. Fleet Forces Command said in a news release Saturday that the ships will get ready in anticipation of getting under way Monday to avoid storm damage.

Adm. Christopher Grady said in a statement that the decision was based on Florence’s current track, which indicates the area could see strong sustained winds and storm surges.

The news release notes that plans could change if forecasts indicate a decrease in the strength or change in the track of the storm.

Swells generated by Florence are affecting Bermuda and could cause dangerous rip currents and coastal flooding Saturday in areas including coastal Delaware and New Jersey, the National Weather Service said.

At 5 p.m. EDT, the hurricane center said Florence’s maximum sustained winds were estimated to be 70 mph (110 kph). The storm was centered about 810 miles (1305 kilometers) southeast of Bermuda and moving west at 5 mph (7 kph).