"This latest briefing is part of the president's monitoring of multiple storms that are predicted to affect the U.S.in the coming days", Sanders said in the statement, adding that the White House is in contact with governor's offices in all the areas affected, including the Carolinas.
"Please be prepared, be careful and be SAFE!"
"North Carolina is taking Hurricane Florence seriously, and you should, too", Cooper said, urging residents to prepare for lengthy power outages after the hurricane comes. Eastbound lanes of Interstate 26 heading into Charleston and US 501 heading into Myrtle Beach will be reversed when the order takes effect.
States of emergency have been declared in North Carolina, South Carolina and Virginia in preparation for Florence's arrival.
Evacuations have already begun along the coastline in North and SC, which are likeliest at this point to suffer a direct hit.
But while wind speed offers an easily quantifiable way to rate unsafe storms, forecasters are warning people not to fixate on that, saying that saltwater from the storm surge and freshwater from heavy rains pose a serious threat, no matter what the top winds are when the hurricane makes landfall.
South Carolina Gov. Henry McMaster ordered a mandatory evacuation of all eight counties on the coast on Monday, The State newspaper in Columbia reported.
A warm ocean is the fuel that powers hurricanes, and Florence will be moving over waters where temperatures are peaking near 85 degrees (30 Celsius), hurricane specialist Eric Blake wrote. Forecasters say Florence will arrive on land as an extremely risky major hurricane by the end of the week.
Hurricane Florence is at the doorstep of North and SC, and she's not going away anytime soon.
Isaac, which the NHC called a small hurricane, was about 1,090 miles east of the Lesser Antilles - a region still recovering from last year's powerful Hurricane Maria - with maximum sustained winds of 75 miles per hour.
Gradual weakening is forecast during the next 48 hours, but Olivia is expected to remain a tropical storm as it moves over the main Hawaiian Islands.
"The bottom line is that there is high confidence that Florence will be a large and extremely unsafe hurricane, regardless of its exact intensity", the hurricane center said.
Helene was weakening, however, and posed no danger to land, the NHC said, while Isaac could bring heavy rain to Martinique, Dominica and Guadeloupe. An average 6-month hurricane season produces 12 named storms, 6 hurricanes and 3 major hurricanes (category 3 or higher).
Quagliariello emphasized the impact of the hurricane, including tropical storm-force winds, could extend more than 100 miles from the storm's center.
"I don't think many of us have ever been through a Category 4".
By 5 a.m. Tuesday, Florence was centered about 975 miles (1,570 kilometers) east-southeast of Cape Fear, North Carolina, and moving west-northwest at 15 mph (24 kph). "We know we can't play around with this", said Jennifer Oosterwyk, who owns the Sugar Britches boutique on Holden Beach and lives in nearby Wilmington.
SC has ordered the mandatory evacuation of its entire coast, and evacuations were also ordered for several North Carolina towns, as Category 4 Hurricane Florence continues her aggressive pursuit towards the states.
The swells will make for rough seas along and well off the U.S. East Coast, Bermuda, the northern shores of the Caribbean islands and the south- and southeast-facing shores of the Canada Maritimes, according to AccuWeather Senior Meteorologist Alex Sosnowski.