For a full week in mid-September, 2009, tropical moisture led to isolated flash flooding across the metro area. With the ground already saturated with 5 to 7 inches of rain, no one was ready for the rainfall that arrived on Sept. 20.
According to Severe Weather Team 2 Meteorologist Katie Walls, moisture sources created the perfect setup. First, a dominant ridge of high pressure over the Northeast induced an easterly wind at the surface, driving in moisture from the Atlantic.
Then, a low pressure system over the Lower Mississippi River Valley induced southerly winds in the lower and mid-levels, driving in Gulf moisture. And finally, the mid and upper levels transported in moisture from the Pacific.
Three-hundred roads were flooded and closed, including both lanes of Interstate 20 west of Atlanta, Interstate 575 at Highway 92, and the Stone Mountain Freeway.
ATLANTA — Austell flooding: 2009
GALLERY: Flooding shuts down I-20
More than a dozen counties were declared disaster areas and elligible for public assistance from FEMA.
Ten people lost their lives, the majority of them died while driving at night.
In Douglas County, where seven people died, hilly terrain played a huge role in the rapidly rising water.
"Once all of that water got through there, any roads, creeks and tributaries and things like that leading into the Dog River is what killed most of the people," said National Weather Service hydrologist Kent Frantz.
Eight gates opened at Morgan Falls Dam, causing record flooding along the Chattahoochee River. The water spilled over onto homes and flooded part of Six Flags Over Georgia. Eighty percent of the Great American Scream Machine was under water.
The gauge on the Chattahoochee was just one of 28 new record crests in north Georgia. A total of 79 river gauges rose above flood stage.
In Buckhead, Peachtree Creek rose to its second highest crest, flooding the parking lot of McCabe's apartment complex.
"It was up to the top flowing into the parking lot into the street, filled up our swimming pool in our complex and all the pool furniture was floating away," McCabe said.