Update as of 10:30 AM:
A Tornado Watch has been issued until 6 PM for the Central Savannah River Area, the Midlands, Pee Dee, and Grand Strand areas.
Original Story from 7:45 AM:
Torrential rain from what is now Tropical Depression Sally is spreading into the Palmetto State, where the threat of widespread flash flooding is expected to increase Thursday.
Numerous flash flood warnings were in effect from Atlanta to Macon, GA associated with same area of heavy rain that is crossing the Savannah River into South Carolina. Rainfall rates are expected to increase to between 1 and 2 inches per hour during the mid and late morning hours of Thursday in the Upstate to the Central Savannah River Area. The heavy rain will become more persistent in the Midlands, Pee Dee, and Lowcountry Thursday afternoon and evening. During the height of the storm, rainfall rates are likely to increase to between 2 and 3 inches per hour. This amount of rain in a short period of time make flash flooding probable.
Heavy rain associated with T.D. Sally will impact much of western SC, central NC and southeastern VA today and into tonight. Widespread flash flooding is anticipated, especially in the Carolinas.
— NWS Weather Prediction Center (@NWSWPC) September 17, 2020
A disturbance in the southwest Gulf will be monitored closely in the coming days. pic.twitter.com/JWkAbFQ9FX
The latest official forecasts from NOAA's Weather Prediction Center are calling for rainfall amounts to average between 3 and 7 inches statewide. Local Weather Service Offices in Greenville and Columbia say that locally higher amounts are expected with the heaviest, most persistent rain bands.
Daytime heating will cause the air to destabilize. Strong lower atmospheric winds combined with this unstable air may spawn a few tornadoes statewide, especially Thursday afternoon and evening.
The heaviest rain is expected to move away from the state overnight Thursday, but river flooding is likely to last into the upcoming weekend as water drains from the Upstate southeastward through the state. As of early Wednesday morning, the forecast for Stevens Creek at Modoc, the Congaree River near Carolina Eastman, and the Pee Dee River at Cheraw were all forecast to reach moderate flood stage Friday or Saturday. Additional rivers are likely to experience at least minor flooding and, depending on the exact amount and location of rain, other rivers may experience moderate or major flooding this weekend and early next week.
Along the coast, persistent easterly winds ahead of Sally, along with astronomical influences from the new moon phase and the perigee, are causing persistent coastal flooding near the times of high tide in the early morning and early evening hours. Coastal Flood Advisories continue for much of the South Carolina coastline. Moderate to major coastal flooding is forecast shortly after sunset near Charleston both Thursday and Friday evenings.
Cooler temperatures are expected behind a cold front over the weekend after Sally moves into the Atlantic waters.