Helene is a category 1 hurricane and one of four active storms in the Atlantic as the hurricane season reaches its peak.
There are no coastal watches or warnings in effect.
A National Weather Service forecaster in Wilmington, North Carolina, said: 'This will likely be the storm of a lifetime for portions of the Carolina coast. Isaac is forecast to gradually weaken over the next few days, and could degenerate into a tropical wave during that time.
The NHC at 11 a.m. on September 12 has issued warnings for Tropical Storm Isaac, which is still moving west about 420 miles east of the island of Martinique.
All watches and warnings that had been issued on neighboring islands were canceled Thursday.
Isaac is moving west at 21 miles per hour.
Forecasters have warned that Storm Helene could pose a danger to life when it bears down on the United Kingdom and Republic of Ireland next week. A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, in this case within 24 to 36 hours.
News 6's Erik Sandoval was live in Wilmington shortly before the storm made landfall.
On the current projected track the centre of this system is forecast to pass between 100 and 150 miles (160 to 240 km) north of Barbados early on Thursday morning.
According to the National Hurricane Center, a burst of deep convection developed Thursday and covered the previously exposed center of Isaac Thursday evening, but there was evidence of northwesterly shear over the cyclone, causing some of the cloud cover to quickly blow off toward the southeast. Earlier forecasts showed that the storm was slated to directly hit around North and SC.
According to analytics firm CoreLogic, the hurricane could wreak more than $170billion (£130billion) in havoc and damage almost 759,000 homes and businesses.
The storm is expected to produce 3 to 5 inches of rain across Martinique, Dominica, and Guadeloupe, with near 10 inches possible in isolated areas, forecasters said.
The remnants of the storm could even end up bringing some drier conditions to the south west of the UK. However, experts remained unsure midday Wednesday where the storm would make landfall in the Carolinas.
It is forecast to move north-westwards, passing the Azores Islands on Saturday and heading towards north-western Europe.
Meteorologists are also keeping an eye on yet another tropical disturbance that's spinning in the western Gulf of Mexico.
Hurricane and tropical storm watches have been posted for several Caribbean islands as a weakening Tropical Storm Isaac continues its trek toward the Leeward and Windward Islands. Regardless of whether a system forms, they say heavy rain and gusty winds are likely along the Texas and Louisiana coast later this week.