Emma Smith, meteorologist with the Exeter-based Met Office, said more details would emerge within the next day over what impact the storm might have.
"On the forecast track, Isaac is anticipated to move near or over the central Lesser Antilles on Thursday and move into the eastern Caribbean Sea later on Thursday night", the NHC said.
At 5 p.m. Tuesday, the center of the tropical storm was located approximately 916 miles east-southeast of St. Croix near 14.6 degrees North, 51.3 west.
"As it tracks towards the United Kingdom it will degrade - it will become an ex-tropical storm". A tropical storm watch was issued for Antigua, Montserrat, St. Kitts and Nevis, and Saba and St. Eustatius.
A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area. Tropical storm conditions are possible within the tropical storm watch area on Thursday.
"Jamaica should monitor the progress of Isaac", the hurricane center said Saturday.
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He said parts of North Carolina had seen storm surges - the bulge of seawater pushed ashore by the hurricane - as high as 10 feet. Officials said some 1.7 million people in the Carolinas and Virginia were warned to evacuate, but it's unclear how many did.
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The news comes just two days after Treasury Secretary Steven Mnuchin extended an invitation to Chinese officials to restart talks. His comment tempered cautious optimism among investors over the US government's proposal for another round of talks with Beijing.
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Downpours and flooding would be especially severe, lasting for days, if the storm stalls over land. "There's nobody left to work". The hurricane has claimed its first victims as it crashed into North Carolina, making landfall near Wrightsville Beach.
Fox News reported that sustained winds were picking up a bit along the North Carolina coast. It is moving northwest at 15 miles per hour, according to the NHC's update at 11 a.m. Sept 12. According to the National Hurricane Center, it has been noted that the use of short, distinctive names in written as well as spoken communications is quicker and less subject to error than the older, more cumbersome latitude-longitude identification methods.
Forecasters say catastrophic freshwater flooding is expected over parts of North Carolina and SC ahead. The center of Helene was about 185 west-southwest of Flores in the Azores Islands, the NHC said in a 8 a.m. EDT advisory. Some regions are expected to receive more than 20 inches of rain from the hurricane and its giant knot of storm clouds.
The storm brought high storm surge near 13 feet and flooding rain as far as 40 miles inland of the storm.
Some of the models show Isaac degenerating into a trough of low pressure in five days.
Tropical Storm Isaac, which passed between the Caribbean island nations of Dominica and Martinique late Wednesday and early Thursday, is now moving nearly due west across the eastern Caribbean Sea.