Isaias strengthened into a Category 1 hurricane hours before it is expected to make landfall along the coast of the Carolinas.
The U.S. National Hurricane Center issued a hurricane warning from South Santee River, South Carolina, to Surf City, North Carolina.
The storm's maximum sustained winds reached 121 kph (75 mph) Monday evening and was centered about 100 kilometers (60 miles) south of Myrtle Beach, South Carolina.
North of the expected landfall area, tropical storm warnings were in effect as far away as Long Island, New York and the Merrimack River in New Hampshire.
Forecasters said the Carolinas and other states in the region can expect rainfall amounts of 7 to 15 centimeters (3 to 6 inches).
Winds along the coast of the Carolinas are expected to exceed 60 kph (37 mph) in some places. The storm is also expected to bring a storm surge of up to 1.5 meters (5 feet) in portions of North and South Carolina.
The mayor of Charleston, South Carolina, John Tecklenburg, said city offices would close early Monday but said he did not think there was a need to issue a curfew.
President Donald Trump declared a state of emergency in North Carolina ahead of the storm's arrival there to free up funds for federal officials to help towns and cities coordinate disaster relief efforts. Trump made a similar declaration Saturday for Florida.