Let me emphasize that this rain is NOT directly associated with Hurricane Joaquin. There is a low pressure system that is sitting over the southeast states, pulling abundant tropical moisture into the region. As the forecast stands now, Joaquin is expected to stay out in the ocean and not make landfall.
Today, showers will be on and off throughout the day. The track will stay wet all day, but the rain will be sporadic. By Saturday morning, the rain should be more constant, and it will likely be heavy at times. This will continue through the end of the race Saturday evening.
If you're camping at the track, I highly recommend that you set up your tent on higher ground. Avoid low lying areas, as they are likely to become flooded. You will especially want to avoid being near Cooper Creek, which runs parallel to the east side of the track, from behind the secondary paddock area past the esses to turn 6. It is possible that the creek will flood.
Despite the rain, I'm sure everyone at the track will have a good time. Remember, a wet day at the race track is better than a dry day anywhere else.