The rain is focused on the Carolinas through Thursday and then will move north.
Tropical Storm Debby is slamming the Southeast with heavy rain after making landfall in Florida as a Category 1 hurricane on Monday.
At least six people have been killed in Florida and Georgia.
The highest rain total so far is south of Tampa, Florida, where about 19 inches of rain fell.
In Georgia, more than 11 inches of rain struck northwest of Savannah, and in South Carolina, 14 inches of rain was recorded between Charleston and Hilton Head Island.
On Tuesday afternoon, Debby is located about 10 miles southeast of Savannah and is crawling north at a very slow speed.
The heavy rain will stretch from Charleston to Wilmington, North Carolina, on Tuesday. Storm surge could reach 4 feet from Savannah to Cape Fear, North Carolina, and tornadoes are possible.
Flash flood warnings are in effect for Savannah, Charleston and Myrtle Beach, South Carolina. Rainfall rates could reach 1 to 2 inches per hour during the heaviest downpours, which will bring more flooding.
The worst of the rain is expected along the South Carolina-North Carolina border through Thursday evening. A rare "high risk" for flash flooding was issued from Charleston to Raleigh, North Carolina, where rain totals could climb to 25 inches through Thursday.
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The threat of severe flooding is very high across South Carolina with Tropical Storm Debby "creeping across our state," South Carolina Gov. Henry McMaster warned on Tuesday.
The rain from the slow-moving storm may be particularly heavy from Myrtle Beach to the North Carolina border, the governor said.
Forty-eight state roads are closed due to flooding and 50 high-water vehicles are at the ready to respond, he said.
More than 90,000 customers remain without power in Florida, more than 24 hours after Debby tore through the state.
"Restoration is taking longer in areas with flooding and heavy vegetation, as crews must wait for the water to recede and clear through debris before they can restore power," Florida Power & Light said Tuesday morning. "Rest assured, we’ll continue working until everyone who can safely receive power is restored. Avoid these flooded areas and stay away from downed power lines."
A curfew in Charleston, South Carolina, has been extended to 7 a.m. Wednesday as the flood-prone city braces for potentially life-threatening flooding.
"Residents are advised to stay off the roads unless there is an urgent emergency," the Charleston Fire Department said.
Charleston is under a flash flood warning. Up to 1 foot of rain has already fallen in the city, with more to come.
Despite weakening since moving over land, Debby is still maintaining its tropical storm status, producing maximum sustained wind speeds of 45 mph.
As of 11 p.m. ET, over 150,000 customers in Florida and Georgia are still without power, according to PowerOutage.us.
With Debby's center about 35 miles west of Brunswick, Georgia, much of the heavy rain and showers have since moved out of Florida (except for the extreme northeastern corner of the state closer to the Georgia border). However, with the storm slowing down even more, Debby will stay stuck over the Southeast for the better part of this week, meandering over Georgia and the Carolinas.
Even though the storm is expected to weaken a bit more overnight, Debby is still expected to bring historic rainfall and life-threatening flooding to portions of southeastern Georgia and the coastal areas of the Carolinas over the next few days. Rainfall totals from this event are expected to reach between 10 and 20 inches.
Already, portions of southeastern Georgia and South Carolina have seen between 3 to 6 inches of rainfall, but with rainfall rates of 1.5 to 3 inches per hour possible, flood alerts remain in effect.
A Flash Flood Warning was issued for Charleston, South Carolina, where rainfall rates between 1.5 and 2.5 inches are expected. Ongoing or new flooding is expected, with an additional 2 to 4 inches of rain possible over the next few hours.
As onshore flow continues, storm surge remains an issue in Savannah, Georgia, and Charleston, South Carolina. Storm surge alerts remain in effect up the Georgia and Carolina coastlines.
Rainfall aside, Debby could also generate some spin-up tornadoes as it swirls over the Georgia-South Carolina border tonight. As a result, a Tornado Watch also remains in effect for parts of southeastern Georgia and South Carolina until 1 a.m. ET.
Over the next 48 hours, Debby is expected to meander back over the Atlantic but will continue to hug the coastline before heading back inland over the Carolinas again. Slight strengthening can't entirely be ruled out as it moves back over water, but ultimately, Debby is expected to weaken once it moves back inland. Strength aside, it will still bring significant rainfall to portions of the Southeast, which will likely lead to catastrophic flooding in some areas.
Debby is expected to eventually drift toward the north/northeast by the end of the week into the weekend. As it heads north, it will likely weaken to a tropical depression or remnant low. Regardless, heavy rainfall is still expected up the I-95 corridor heading into this weekend.
-ABC News meteorologist Shawnie Caslin Martucci
