That's almost double the wave heights documented on Tuesday, when the NHC said satellites had observed "an expansive area of wave heights 12 feet or greater" circulating around Hurricane Florence and peak waves of 45 feet near its center.
Shepard Smith and Flaherty said reports showed storm surge from the system is likely to be felt dozens of miles inland, including along the Neuse River Basin - which stretches inward from New Bern toward Rocky Mount and Nashville, N.C.
The latest guidance suggests that the strongest winds will occur along the south and west coasts, where gusts could exceed 130-140 kph.
Federal states of emergency have been declared in all three states, and collectively about 1.5 million people have fled the coast under mandatory evacuation orders.
Helene is now 2,065km south-southwest of the Azores in the Atlantic and Met Éireann said the storm would approach the south coast by Tuesday. "This storm is extremely risky".
Isaac was a hurricane Sunday night but downgraded when maximum sustained winds fell below 74 miles per hour.More news: Serena Williams Fined $17000 For US Open Controversy
There is the potential for damaging winds with gusts up to 70mph possible, with sustained winds of 30 to 40mph.
The 8 a.m. forecast on Hurricane Florence reinforces projections that the storm's path will shift slightly to the southeast as it closes in on the Carolinas.
A Tropical Storm Watch which had been issued for St. Kitts and Nevis, Montserrat, Barbuda and Antigua was also expected to be discontinued by Thursday evening.
"The centre of Hurricane Isaac was located near latitude 14.7 North, longitude 43.9 West. Isaac was moving towards the west near 14 miles per hour". Earlier forecasts showed that the storm was slated to directly hit around North and SC.
The agency is also monitoring a tropical disturbance that has a 60 percent chance of forming a tropical storm.
Winds of tropical storm strength could reach Puerto Rico on Friday morning. Current estimates have Isaac passing nearly 150 miles south of St. Croix early Friday morning.