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.
The NHC is estimating that as many as 20 inches of rain could fall in some places along the southern North Carolina coast while bringing in excess of 10 inches of rain in parts of SC. Maximum sustained winds for Isaac are near 70 miles per hour.
Florence, a potentially life-threatening Category 4 hurricane, is on track to make landfall in North Carolina or SC on Thursday (Sept. 13).
As three powerful storms march one by one across the Atlantic Ocean toward the U.S. East Coast and the Caribbean, a fourth is getting ready to roll over the Hawaiian Islands.
On the forecast track, Isaac will move over the eastern and central Caribbean Sea during the next few days.
Rainfall amounts of 2 to 4 inches with isolated amounts up to 6 inches over elevated terrain are forecast across Martinique and Guadeloupe.
Some fluctuation in wind speeds are expected, and weakening forecast Thursday, but it's still expected to be a fierce storm triggering risky flooding. Isaac was moving to the west at 21 miles per hour with maximum sustained winds of 45 miles per hour.
Surf swells from Isaac could be life-threatening and coastal flooding is a risk in the Lesser Antilles.
"There are no coastal watches or warnings in effect", said the NHC in its 11 a.m. September 12 update.
Another system in north-central Atlantic waters was upgraded to a subtropical storm, Joyce, Wednesday afternoon as it approached the Azores.
Isaac became the fifth hurricane of the season late Sunday and was initially expected to strengthen, potentially becoming a Cat 2 storm with 100 miles per hour winds, as it crossed warm ocean waters.