While a tropical storm watch is in effect for St. Kitts and Nevis, at Pond Hill, Nevis, forecaster Harry W. Hallstrom said, "Isaac is getting ripped apart with wind shear. At 2:00 pm today, the centre of Tropical Storm Isaac was located near 14.9W 62.5N or about 130 km west-southwest of Dominica, moving W at 30 km/h with maximum sustained winds of 75 km/h", the Met Office said.
The NHC said an area of low pressure is expected to develop near Bermuda late this weekend or early next week and gradual development is possible after that time while the system drifts westward over the western Atlantic.
"This storm will bring destruction to North Carolina", Gov. Roy Cooper said Thursday morning.
At 800 AM AST (1200 UTC), the center of Tropical Storm Isaac was located near latitude 14.4 North, longitude 54.1 West. Isaac is moving toward the west near 15 miles per hour (24 km/h), and this general motion is expected to continue through the weekend. Some fluctuation in wind speeds are expected, and weakening forecast Thursday, but it's still expected to be a fierce storm triggering risky flooding.
All of the islands under watch were significantly impacted by Hurricanes Maria or Irma last September, with some of them still trying to rebuild.
Tropical Storm Isaac is expected to produce total rainfall accumulations of 2 to 4 inches with isolated amounts up to 6 inches across Martinique, Dominica, and Guadeloupe, especially over elevated terrain. Near the coast, the surge will be accompanied by large waves. This rainfall may cause unsafe flash flooding, N.H.C. said.
Helene is a category 1 hurricane and one of four active storms in the Atlantic as the hurricane season reaches its peak.
The turbulent weather is coming off the back of one of number of major storms now raging in the Atlantic, another of which, Hurricane Florence, has caused mass evacuations on the east coast of United States this week. If the rain bands persist, the National Weather Service may raise the flash flood watch to a flash flood warning triggering the emergency alert system.
Joyce could become a tropical storm within the next day or so.
"A turn toward the north and northeast with an increase in forward speed is expected during the next few days", according to the agency.
With the ground already saturated from recent rain, another drenching from Florence combined with winds could easily lead to trees being uprooted and widespread power outages, he said.