The hurricane center's description of a Category 4 hurricane begins with "catastrophic damage will occur".
Storm watches related to the hurricane started at Edisto Beach and stretched north through North Carolina to the Virginia border as of Tuesday morning.
As of 11 a.m. EDT on Monday, Florence has been upgraded to a Category 4 storm. Additional strengthening is expected over the next day or two. It could briefly strengthen to near category 5 strength at some point late Tuesday or Wednesday. Gradual weakening is forecast during the next 48 hours, but Olivia is expected to remain a tropical storm as it moves over the islands.
Everyone is encouraged not to just focus on the storm's eye or center, as Florence is growing in size. Regardless of category, it will be large impact. Hurricane force winds now extend 40 miles from the eye.
A hurricane hunter plane found Florence strengthening quickly, reaching top winds of 85 miles per hour (140 kph) Sunday evening after crossing the 74 miles per hour threshold from tropical storm to a hurricane earlier in the day.
Authorities warned of life-threatening coastal storm surges and the potential for Florence to unleash prolonged torrential rains and widespread flooding, especially if it lingers inland for several days. The center warns that such storms will snap or uproot most trees and down power poles and that power can be out in some areas for weeks or months. Even before the evacuation order, Dare County emergency officials warned that rough seas and strong rip currents already were creating risky conditions. Trump tweeted, adding: "WE are here for you". Residents in certain areas of both states have been ordered to evacuate their homes. He told The Chronicle Sunday that once Florence hits land, destructive winds and huge rainfall flooding may take hold of the area.More news: Djokovic overcomes dogged Millman to reach semis
U.S. President Donald Trump, whose administration was harshly criticized as being slow to respond to Hurricane Maria in Puerto Rico, cancelled a political rally planned for Friday in Jackson, Mississippi, over safety concerns related to Florence, his campaign said.
Isaac is a Category 1 hurricane that's blowing winds between 74-95 miles per hour.
Meanwhile, two other storms were also spinning in the Atlantic.
Forecasters said parts of North Carolina could get 20 inches of rain, if not more, with as much as 10 inches elsewhere in the state and in Virginia, parts of Maryland and Washington, D.C. If the storm stalls longer than expected, much higher rainfall amounts would be possible.
Residents along the Southeast and Mid-Atlantic coasts should continue to prepare for a major hurricane landfall and have an evacuation plan.
The United States was hit with a series of high-powered hurricanes a year ago, including Hurricane Maria, which killed about 3,000 people in Puerto Rico, and Hurricane Harvey, which killed 68 and caused an estimated $1.25 billion in damage from catastrophic flooding in Houston. Rivers are high, and the storm will be moving slowly when it arrives, exacerbating the danger, Rossi told USA TODAY. Rescuers may not be able to reach you if flood waters rise around your location. Hurricanes are a bit unpredictable at this stage, so stay tuned as details can change over time.