September 10 is the statistical peak of hurricane season (and September 9 was the anniversary of the 1900 Galveston hurricane), and it is clearly living up to the hype. It will move between Bermuda and the Bahamas on Wednesday and Thursday, before approaching the southeastern US coast, the NHC said in an advisory. The storm was centered about 835 miles (1340 kilometers) southeast of Bermuda and moving west at 7 mph (11 kph).
Isaac's maximum sustained winds have increased to near 70 miles per hour (110 km/h) with higher gusts.
"The bottom line is that there is increasing confidence that Florence will be a large and extremely unsafe hurricane, regardless of its exact intensity", forecasters said.
The storm was upgraded Monday morning to a Category 3 hurricane, but grew to Category 4 a short time later, the National Hurricane Center said in its latest update Monday.
Damaging tropical storm force winds may begin as early as Tuesday afternoon across the Big Island and Maui.
Because the storm is so small, forecasters are less certain about how intense Isaac may become. People living well inland should prepare to lose power and endure flooding and other hazards, he warned.
The U.S. Navy is making preparations this weekend for its ships in the Hampton Roads area to leave port as Tropical Storm Florence approaches the East Coast.
As of 5 a.m., Hurricane Florence has reached maximum winds speeds of 105 miles per hour.
While the hurricane center says Isaac is a very small hurricane, its intensity could fluctuate as it approaches the Caribbean - but it's still expected to be at or near hurricane strength by the time it reaches the Lesser Antilles.
As of 5 p.m., Sunday, the storm was 720 miles souteast of Bermuda and moving west.
Further to the east, forecasters are also watching hurricanes Isaac and Helene.
A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours. Paul is not expected to make landfall anywhere, but Olivia could threaten Hawaii.
Hurricanes Helene and Isaac are not expected to hit the USA mainland. Another disturbance in the eastern Atlantic has a 40% chance of organizing into a tropical depression. That storm was centred 185 km south southeast of the islands.
"A high-pressure ridge building to the north and northwest of Florence is expected to steer the hurricane west-northwestward to northwestward at a much faster forward speed over the southwest Atlantic during the next few days".