Isaac brought up a very humid tropical air mass into the mid state as the system passed to our west.
This will allow pop up type showers and t'storms to break out quite easily today when you add a little heat. We'll put today's (Saturday) chances at 50%
But the rain and t'storm bands extending southward out of what is now Tropical Depression Isaac will push into Middle TN Sunday and Monday as the low passes to our north.
That will increase rain and t'storm chances to 80% both Sunday and Monday.
When those rain bands push through the rain could be quite heavy for a while, causing some localized flooding, so be careful not to hydroplane when driving.