Update as of 10:30 AM Monday:
Heavy rain has overspread much of the Palmetto State and it’s expected to last into early Tuesday morning resulting in a significant risk for flash flooding.
The National Weather Service has continued Flash Flood Watches for the Midlands, Pee Dee, Grand Strand, and Lowcountry. Radar data and rain gauges throughout the state have recorded between 1 and 3 inches of rain since the storm began earlier Sunday. Parts of the Midlands and Lowcountry have received upwards of 4 inches. An additional 3 to 5 inches of rain along and east of Interstate 95 are expected before the storm winds down on Tuesday. Another 1 to 3 inches are forecast across most of the rest of the state.
A unusually strong low pressure in the upper levels of the atmosphere is spinning over the Florida Panhandle Monday morning. Moisture from the Gulf of Mexico and from the Atlantic is rotating around this low and is focused directly over South Carolina. The low is moving slowly and is not expected to move offshore until Tuesday. Rain is expected to continue over much of the state tonight before finally exiting the Lowcountry by noon Tuesday.
Gusty east winds, combined with the heavy rain, has prompted Coastal Flood Advisories for the Charleston area. The National Weather Service in Charleston says additional coastal flooding could occur during the times of high tide through the middle of this week.
A Flash Flood Watch has been issued for most of the South Carolina Midlands and Lowcountry regions through Monday as a widespread heavy rain event begins to unfold. Nearly all of the Palmetto State will receive at least two inches of rain, and storm totals in some areas southeast of I-95 could top eight inches.
Forecasters at the National Weather Service are advising residents in flood prone areas to be prepared to protect life and property. Local authorities may be forced to close many roads over the next two days, and evacuation orders may be required along some rivers.
The heaviest rain will this storm system will fall late Sunday night through Monday afternoon, as an area of low pressure moves closer to the Atlantic Coast. Rainfall rates of up to one inch per hour could cause a rapid rise in streams and creeks, resulting in flash flooding of low-lying areas. This will be especially true in and around the Charleston area, where forecast data suggests the heaviest rain will fall through the period.
Many rivers across South Carolina are also expected to flood following the departure of this storm. Flood Warnings have already been issued for the Santee River near Jamestown, the Savannah River near Clyo, and the Ogeechee River near Midville. Skies will gradually clear on Tuesday and Christmas Day as the storm system exits, but flooding along these rivers may linger for several more days.