At 5 o'clock Sunday morning, the Department of Disaster Management (DDM) said Tropical Storm Isaac was located near latitude 14.5 north and longitude 38.1 west.
The hurricane center says "catastrophic" Category 4 storms generate sustained winds of at least 130 miles per hour.
NHC forecasters say that Florence is expected to rapidly strengthen into a major hurricane by Monday, and is forecast to remain an extremely unsafe major hurricane through Thursday. The National Weather Service in Morehead City predicts that Florence will be renamed a hurricane on Sunday.
The Navy said all ships in Virginia's coastal Hampton Roads area were preparing to leave port for open seas Monday.
Officials in the Carolinas, as well as Virginia, began preparing Friday for the storm's potential major impact.
Cooper's emergency declaration makes it possible to waive the state's transportation rules so North Carolina farmers can harvest and transport their crops to market faster.
On its current trajectory, winds from the hurricane could reach the southeastern United States late on Wednesday, with Florence possibly making landfall around the Carolinas on Thursday or Friday.
La cote de popularité d'Emmanuel Macron continue de chuter
Le média français évoque plusieurs raisons de cette chute de popularité du Président. En effet, il est passé à 35% de satisfaits, contre 38% en juillet.
Florence is expected to be back at Cat 4 as it approaches the Atlantic Coast this Wednesday to Thursday. There were no coastal watches or warnings in effect as of Sunday morning.
"There is an increasing risk of life-threatening hazards from storm surge and heavy rainfall from the Carolinas into the mid-Atlantic region", the hurricane center tweeted. It is expected to regain Category 1 status Sunday, with further strengthening anticipated as Florence moves over warmer ocean waters.
State agencies are working closely with localities to identify any needs in advance of the storm, and to pre-position resources where they will be most effective.
This enhanced satellite image made available by NOAA shows Tropical Storm Florence, centre, in the Atlantic Ocean on Saturday.
Residents in North Carolina and other East Coast states should pay attention to the storm and begin to think about hurricane plans.
As a public safety note, the south shore will experience unsettled surf conditions associated with Hurricane Florence, and the public is encouraged to use caution on those beaches..
The three systems - Florence, Isaac and Helene - come right before the Atlantic hurricane season hits its peak Monday.