Isaac a threat to Fla. Keys, northern Gulf Coast

Shira Edllan Gervasi, of Israel, puts her name on plywood protecting a storefront in Key West, Fla., in anticipation of Tropical Storm Isaac on Saturday, Aug. 25, 2012. Isaac's winds are expected to be felt in the Florida Keys by sunrise Sunday morning. (AP Photo/Alan Diaz)Forecasters say a strengthened Tropical Storm Isaac is bearing down on the Florida Keys.