The last 30 days have been very wet in parts of Florida, although the southern tip is quite dry and is in extreme drought. The map below from http://water.weather.gov/precip shows that some areas of western Florida north and south of Tampa have an excess of 8 inches in just the last month. If the path of TS Erika moves over those areas, flooding of many areas is likely.
The amount of rainfall from a tropical storm can be hard to predict, but meteorologists use a very rough rule of thumb to estimate how much it might be: take 100 and divide it by the forward speed of the storm and that is the number of inches of precipitation to expect. Thus, if the storm is moving at 20 miles per hour, you might expect to see 100/20=5 inches from the storm. If the storm is moving at 3 miles per hour, then you would expect 100/3=33.3 inches. Tropical Storm Alberto in 1994 parked itself over southern Georgia in 1994 and dropped massive amounts of rain over the area, including Albany and Macon. While the precipitation did not reach 33 inches, some areas had over 20 inches from that storm.
We won’t know how (or if) TS Erika survived the passage of the storm center over the island of Hispaniola today and where the future path will be until tomorrow, but even if the storm weakens and does not redevelop, that mass of rain and humid air is still likely to progress over the area, causing showers and potentially heavy rain in some areas of the Southeast. So your hurricane preparations should include preparing for and knowing what to do in flooding conditions. Remember, the path of the storm is very uncertain now and the models do not agree on where it will go, so it is essential to keep watching forecasts if you are in an area that might be affected by the storm.