Forecasters on Sunday upgraded Tropical Storm Florence to a hurricane, saying it was strengthening and taking aim at North and South Carolina, where it could make landfall by the end of the week.
“We expect a rapid intensification of Florence tomorrow,” Dennis Feltgen, a spokesman for the National Hurricane Center, said on Sunday. “We expect it to be a major hurricane when it makes landfall by Thursday night or early Friday.”
By Monday, Florence was expected to intensify to a Category 3 hurricane, with winds of 111 to 130 miles per hour, up from a Category 1 on Sunday. On Sunday evening, the center said Florence would “remain an extremely dangerous major hurricane through Thursday.”
Mr. Feltgen cautioned that heavy rains could prove more damaging than the high winds. He said Florence could be a “major event,” affecting all of South Carolina in particular, not just its coast, with “historic freshwater rainfall.”
“There is every definite possibility of two life-threatening impacts,” he said. “The storm surge at the coast and freshwater flooding from the prolonged rain.”
The National Hurricane Center advised residents along the southeast coast to prepare. Virginia and North and South Carolina have already declared states of emergency.
“It is coming straight in,” Gov. Henry McMaster of South Carolina said at a news conference on Sunday. “We are prepared to the nth degree. We’ll know more tomorrow, but based on what we know now, the situation is such that it is time to begin preparations.”
The governor of North Carolina, Roy Cooper, also advised residents to get ready.
“State emergency management, transportation, health experts and others are making sure North Carolina is prepared for the storm, and I urge the public to review your emergency plans and gather your supplies now,” he said.
Hurricane Florence was part of an overall busy weather pattern as forecasters tracked four tropical storms in the Atlantic and Pacific Oceans on Sunday.
Tropical Storm Isaac was strengthening and the National Hurricane Center expected it to be upgraded to a hurricane by Sunday night. It was headed toward the Caribbean, but no warnings had been posted.
In the Atlantic, Tropical Storm Helene was close to the Cabo Verde Islands off the coast of Africa and was expected to go out to sea after it passes the islands.
In the Pacific, Tropical Storm Paul was southwest of the southern tip of Baja California. Forecasters expected it to remain a tropical storm and head out into the open water.
A second tropical storm in the Pacific, Olivia, could threaten Hawaii in a couple of days, but it was too early to tell, Mr. Feltgen said.
Having five systems in the Western Hemisphere is fairly common for this time of year. Sept. 10 is considered the statistical peak of the hurricane season, Mr. Feltgen, said, adding, “This is right on target.”
Last year at this time, Hurricanes Irma, Jose and Katia were billowing in the Atlantic basin.
“This is not unusual,” Mr. Feltgen said. “But there is no such a thing as just a storm.”
Separately, parts of Ohio saw close to nine inches of rain over the weekend brought by the remnants of Tropical Storm Gordon. Ben Gelber, a meteorologist at the NBC affiliate WCMH-TV, described the rain as “really excessive,” noting that most of the state got three to five inches and some pockets saw as much as nine inches.