Tapping into moisture from the nearby Hurricane Joaquin, a developing surface low brought heavy, continuous rain to southeastern States, with the worst effects concentrated in South Carolina where catastrophic flooding occurred.

The event culminated in South Carolina on October 4 when numerous rivers burst their banks, washing away roads, bridges, vehicles, and homes.

[3] On September 29, 2015, a cold front moved southeast across the Eastern United States and produced widespread heavy rain.

[5] By October 2, the frontal system stalled offshore and a 1000 mbar (hPa; 29.53 inHg) surface low developed just east of the Florida–Georgia border.

[1] A strengthening ridge to the northeast created a tighter pressure gradient, resulting in a large area of onshore gales.

[16] On October 2, a plane crashed along the South Carolina side of Lake Hartwell, killing all four occupants.

[17] On October 3, the Charleston Historic District was brought to a virtual standstill with most roads closed because of flooding.

Through the evening of October 3, highway patrol reported 500 traffic accidents and 104 flooded roads.

[19] Early on October 4, the National Weather Service issued flash flood emergencies for Berkeley, Charleston, and Dorchester counties.

[30] A mandatory evacuation was issued for areas downstream of the Overcreek Dam on October 5 after the structure was breached.

[11] The head of the South Carolina National Guard compared damage from the floods to Hurricane Hugo in 1989, which caused $9.5 billion in economic losses.

Reinsurance company Aon Benfield indicated losses from the floods would be well in excess of $1 billion, with a large portion coming from uninsured homeowners.

[33] In Virginia, heavy rains resulted in numerous traffic accidents; state police responded to 375 incidents on October 3.

[34] The James River approached flood levels, and hundreds evacuated low-lying areas in Lancaster County on Virginia's Northern Neck.

[36] Several days of continuous onshore flow caused significant coastal flooding and beach erosion in New Jersey.

[38] On October 2, a fishing boat with five crew capsized amid 10 to 15 ft (3.0 to 4.6 m) swells in Jamaica Bay, near Floyd Bennett Field along the south coast of Long Island, New York.

Widespread flooding washed out roads and bridges, impairing travel; Hoyt was rendered inaccessible.

[43] President Barack Obama declared parts of South Carolina a disaster area, making federal aid available in Charleston, Berkeley, Dorchester, Georgetown, Horry, Lexington, Orangeburg, Richland, and Williamsburg Counties.

[44] Calhoun, Clarendon, Kershaw, Lee, and Sumter counties were later added to the list of federal disaster areas.