NOAA Hurricane Hunters have been flying constantly from Lakeland Linder International Airport, right into Hurricane Florence.
Some fluctuations in strength are expected through Thursday morning.
Updated NHC forecasts showed the storm lingering near the coast of the Carolinas, carrying days of heavy rains that could bring intense inland flooding from SC to Virginia.
Forecasters said conditions are still good for Florence, a Category 4 hurricane, to strengthen a little as it moves over very warm waters.
Since Tuesday, forecasts have shifted the storm track towards the south and southwest after it reaches the coast, which could increase the storm's severity in coastal SC through Myrtle Beach and Charleston and even into parts of Georgia.
As of 11 p.m. EST, the storm was centered 280 miles east southeast of Wilmington, North Carolina, and was moving northwest at 17 mph.
Meteorologists are warning of potentially catastrophic flooding in the area, with isolated amounts of up to 40 inches of rain expected in parts of SC. The Category 4 storm is likely to produce "catastrophic" flooding in the eastern Carolinas, as well as destructive winds.
Col. Glenn McNeill with the North Carolina State Highway Patrol said troopers are on standby statewide to assist where needed. The only exception was Edisto Beach - that and other areas to the north remain under evacuation orders.More news: Chelsea boss Maurizio Sarri: I've decided our captain
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A storm surge warning has been issued from South Santee River, SC, to Duck, NC, and the Albemarle and Pamlico Sounds.
News that the storm could plow through SC after landfall came shortly after McMaster lifted his mandatory-evacuation order for Beaufort County and many other areas south of Charleston.
A tropical storm watch is in effect for north of the North Carolina/Virginia border to Cape Charles Light, VA, and for Chesapeake Bay south of New Point Comfort.
She said it will become a "major flooding event".
The pivot in the forecasted track of Florence led Georgia's governor to declare a state of emergency for all 159 counties, home to 10.5 million people.
And if that isn't enough, Subtropical Storm Joyce formed in the North Atlantic Tuesday afternoon, but it's not expected to hit the U.S. The system is expected to drift to the southwest in the coming days.
President Trump says the Federal Emergency Management Agency and first responders are poised to help - but he also warned people to get out of the storm's path.
Tropical disturbance Invest 95L as of Wednesday morning.