Seemingly endless rain in Beaufort County and across South Carolina is the result of warm weather systems moving south this summer, a National Weather Service meteorologist said Sunday.
The high-pressure, subtropical systems that kept warm weather in the area and thunderstorms and rain out of it were pushed to the southeast along with the jet stream those pressure ridges move along, said weather service meteorologist Pete Mohlen in Charleston.
The lack of high pressure systems means less downward force, which allows air to get higher and create more storms, Mohlen said. The jet stream moving south also allows more northern thunderstorm systems to reach into the state that normally would be kept out by the high pressure systems.
Mohlen said Savannah-Hilton Head International Airport, the closest National Weather Service measured location to Beaufort County, has received 7.34 inches of rain since July 1, twice the normal average of 3.61 inches. In total, the airport has seen 35.16 inches of rain since the start of 2013, Mohlen said.
"Since June 1, there's been 30 measurable days of rainfall out of 51 total days," he said. "That's pretty high. It's been a pretty wet year so far."
On Thursday, the Savannah River crested in Jasper County at 18.38 feet, its highest level in that area since 1993. Fifteen homes near the river on Tom Goethe Road were evacuated after the dirt sections of the road washed away, Jasper County Office of Emergency Management director Wilbur Daley said Thursday.
Heavy rainfall in the northern areas of the Savannah River basin, especially near the two lakes that feed the river, were the cause of the rising water level in its southern sections.
In Aiken County, rainfall measured near Augusta through the first 10 days of July was about 600 percent of the normal average, according to a press release from the Savannah District U.S. Army Corps of Engineers.
The high rainfall caused an increase of water releases at the J. Strom Thurmond Dam and the New Savannah Bluff Lock and Dam along the northern parts of the Savannah River, the release said.
North of Augusta, heavy rain in Anderson County forced water releases at Lake Hartwell on July 9. The lake's water level came about five inches short of the record crest, 665.6 feet, set in April 1964, according to a report from the Associated Press.
At 5 p.m. Sunday, the river had receded back to about 18 feet even, Mohlen said, but that section of the river will remain on a moderate flood warning through most of next week. Continued heavy rainfall could mean a secondary crest for the river in the wet season, he added.
Daley said it could take weeks for the river to recede to a level where displaced residents could return to their homes.
Follow reporter Matt McNab at twitter.com/IPBG_Matt. The Associated Press contributed to this report.