(RNN) – Although Florence weakened to a Category 2 hurricane late Wednesday night, the storm is still expected to produce catastrophic flooding throughout the Carolinas when it makes landfall Thursday night or Friday.
The impact of Florence will be widespread, with destructive winds, life-threatening storm surge, dangerous surf, torrential rainfall, flooding and the potential for tornadoes.
However, forecasters say the storm's biggest threat is how much rain it is expected to produce.
Florence is forecast to move slowly over the Carolinas after making landfall Thursday night or Friday, according to the National Hurricane Center. The slow forward motion means Florence will batter the area with heavy rainfall, producing up to 40 inches in coastal North Carolina and northeastern South Carolina.
The NHC notes that amount of rainfall would "produce catastrophic flash flooding and prolonged significant river flooding."
The rest of South and North Carolina as well as southwest Virginia may see up to 24 inches of rain.
People in areas vulnerable to the dangerous hurricane, particularly those in coastal regions, have fled ahead of the storm.
About 800 flights in the region have been canceled ahead of the storm, CNN reported.
Hurricane Florence's path could affect the homes of more than 5 million people, and more than 1 million of them have been ordered to evacuate.
In the 5 a.m. ET advisory, Florence was 205 miles east-southeast of Wilmington, NC, packing maximum-sustained winds of 110 mph and moving to the northwest at 15 mph.
The storm is not expected to change much in strength before making landfall.
States up and down the East Coast have a great potential for severe weather.
Washington, DC, Mayor Muriel Bowser and the governors of North Carolina, South Carolina, Virginia, Georgia and Maryland have declared states of emergency. President Donald Trump declared a state of emergency on the federal level Tuesday for the Carolinas and Virginia.
More than 10 million people live in areas under warnings or watches for hurricane- or tropical storm- force winds, CNN reports.
Hurricane-force winds now extend up to 80 miles and tropical-storm-force winds extend up to 195 miles from the center of the storm.
A hurricane warning is in effect for South Santee River, SC, north to Duck, NC, and the Albemarle and Pamlico Sounds.
A hurricane watch is in effect for Edisto Beach, SC, to South Santee River, SC.
A tropical storm warning is in effect for north of Duck, NC, to Cape Charles Light, VA, and for Chesapeake Bay south of New Point Comfort.
In addition, the threat of storm surges looms for areas in the path of the storm, meaning life-threatening inundation from rising water moving inland is possible in the next 36 hours.
Areas along the coast from Cape Fear to Cape Lookout, NC, including the Neuse, Pamlico, Pungo and Bay rivers may experience storm surges from 9 to 13 feet.
Other areas facing a surge include:
- North Myrtle Beach to Cape Fear, 6 to 9 feet
- Cape Lookout to Ocracoke Inlet, NC, 6 to 9 feet
- South Santee River to North Myrtle Beach, SC, 4 to 6 feet
- Ocracoke Inlet to Salvo, NC, 4 to 6 feet
- Salvo to North Carolina/Virginia border, 2 to 4 feet
- Edisto Beach, SC, to South Santee River, 2 to 4 feet
The full impact of storm surge on the coast will depend on whether the storm's arrival coincides with high tide. However, the surge is expected to be accompanied by large and destructive waves, regardless of when the storm arrives.
By early Saturday morning, Florence is expected to have weakened to a tropical storm, and by early Sunday, it will be a tropical depression.
The East Coast isn't the only area facing the brunt of a storm. Tropical Storm Olivia made a double landfall in Hawaii Wednesday morning, first in west Maui then Lanai, KHNL reports.
Torrential rains brought about significant flooding in some areas, with the rains expected to continue over Oahu through Thursday.
Olivia is the first tropical cyclone to make landfall on Maui in modern history, National Weather Service forecasters said.
Elsewhere in the Atlantic basin, Tropical Storm Isaac will strike the islands of the Lesser Antilles, which are expected to experience tropical storm conditions and rainfall amounts of up to 6 inches. Puerto Rico and the Virgin Islands face possible isolated amounts of 3 inches.
Hurricane Helene is moving north, where it's expected to become a tropical storm Thursday. It is expected to turn away from the U.S.
Subtropical Storm Joyce, which formed in the North Atlantic Tuesday, is also not expected to hit the U.S. It is forecast to become a tropical storm in the next day or so while drifting to the southwest.
Another disturbance is swirling around in the Gulf of Mexico. That system could develop into a tropical depression by Friday. The NHC is encouraging officials in northeastern Mexico, Texas and Louisiana to monitor its progress.