The weather system is now responsible for disorganized showers and thunderstorms, but has a 20 percent chance of developing into a tropical system in the next two days and a 40 percent chance in the next five.
A second system in the central Atlantic has a much lower chance of developing (10 to 20 percent).
Regardless of development, the NHC stressed, the system is expected to bring heavy rainfall and gusty winds to portions of the Lesser Antilles beginning late tomorrow.
An Air Force Reserve Hurricane Hunter aircraft is scheduled to take a closer look this afternoon.
The NHC said some gradual development of that system is possible over the next few days while it moves slowly toward the west-northwest or northwest over the open Atlantic Ocean. The National Hurricane Center gives one of them 50 percent odds of forming and the other 30 percent odds of forming during the next five days.
Meanwhile, in the eastern Pacific there is a full-fledged hurricane. It was moving to the west at 13 miles per hour (20 kph).
The storm was heading in the general direction of Hawaii, but forecasters said it is expected to lose strength in the coming days.
This area is about 2,400 miles from Myrtle Beach and poses no threat to land at this time.