Tropical Storm Beryl made landfall shortly after midnight, eastern time weather officials said.
Little change in strength is expected, and steady weakening is forecast once the storm moves inland, according to the National Hurricane Center.
Hundreds of campers and day-trippers to Georgia's Cumberland Island National Seashore were ordered to leave as Beryl was poised to make landfall late Sunday night or Monday morning in northeastern Florida, the National Parks Service said.
Campers were told to be on the last ferry off the island at 4:45 p.m. Sunday, said Pauline Wentworth of the Parks Service. Returning ferries Sunday afternoon have averaged about 100 passengers, she said.
In Florida, the Jacksonville Aviation Authority said Sunday night that all airlines, expect JetBlue and Delta, canceled the day's remaining incoming and outgoing flights. It was not immedaitely clear how many flights were affected.
Tropical storm conditions were forecast for areas of the Atlantic coast from northeastern Florida to southern South Carolina.
Beryl will dump several inches of rain and bring high winds and coastal flooding to the area, putting a damper on the holiday weekend.
As of 11 p.m. Sunday, the center of Beryl was about 35 miles east of Jacksonville, Florida, and about 75 miles south-southeast of Brunswick, Georgia, forecasters said. Packing maximum sustained winds of 70 mph with higher gusts, Beryl was moving west at about 7 mph. A storm is classified as a Category 1 hurricane if it reaches sustained winds of 74 mph.
A tropical storm warning was in effect from the Volusia-Brevard county line in Florida to Edisto Beach, South Carolina.
"Tropical storm conditions are already affecting the coast of northeastern Florida and southeastern Georgia. These conditions will continue to spread inland tonight and Monday," the hurricane center said. Hurricane-force gusts of at least 74 mph are possible in the region.
"I've been through a couple, but thank God, we made it through," Flagler County, Florida, resident Jimmy Poole told CNN affiliate Central Florida News 13. "I know we've got to board the windows and be careful in the water, and I know the news is going to tell us what to do."
A storm surge and high tide will cause coastal flooding of 2 to 4 feet along the Florida and Georgia coasts and 1 to 2 feet along coastal South Carolina, forecasters said. Dangerous surf conditions including rip currents are expected through the weekend in the warning area.
Beryl is expected to dump 4 to 8 inches of rain along parts of the Southeastern coast, with isolated maximum amounts of 12 inches. Tropical storm-force winds of at least 39 mph extend outward up to 115 miles from the storm's center, the hurricane center said.
After landfall, the forecast track shows Beryl circling around into southeastern Georgia and South Carolina before heading back out to sea Tuesday or Wednesday.
The storm will bring much needed rain to the area, most of which is experiencing an "extreme" or "exceptional" drought, according to the University of Nebraska-Lincoln, which tracks drought conditions nationwide.
While some rain may be welcome, officials are warning of dangerous rip currents and strong winds.
"Residents and visitors along the northeast coast should closely monitor this system and use caution on roadways," said Amy Godsey, Florida Division of Emergency Management state meteorologist, according to Central Florida News 13.
On Sunday morning, officials closed waters off Tybee Island, Georgia, to public use, according to CNN affiliate WSAV in Savannah, Georgia. The area was experiencing rain from rain bands associated with Beryl and waves of about 4 to 6 feet with strong rip currents.
A day earlier Tybee Island lifeguards conducted 48 rescues because of rip currents, WSAV said. It was the island's second-busiest day on record for rescues behind July 3 of last year, officials said.
The Federal Emergency Management Agency said in a statement that it was monitoring Beryl through its regional office in Atlanta, and deployed a liaison to the Miami-based National Hurricane Center to share information with the regional office and affected states.