Here is just one example, taken from "The Spanish Borderlands", by Bolton:
"The slow-moving treasure fleets from Mexico and Havana sailed past Florida through the Bahama Channel, which Ponce de León had discovered, and on to the Azores and Spain. The channel was not only the favorite hunting place of pirates — so that the Spanish treasure ships no longer dared go singly but now combined for protection; it was also the home of storms. The fury of its winds had already driven too many vessels laden with gold upon the Florida coast, where as yet there were no ports of succor. Cargoes had thus been wholly lost, and sailors and passengers murdered by the savages. To these dangers was added the fear that the French designed to plant a colony on the Florida coast near the channel, so that they might seize Spanish vessels in case of war, for not one could pass without their seeing it. So, on Philip's order, Viceroy Velasco bestirred himself to raise colony, not only for Coosa but for some other point in Florida. The other point selected was Santa Elena, now Port Royal, South Carolina."
In fact, Santa Elena was made the capital of La Florida.
South Carolina and Georgia did not become "infested" with English until well into the 18th Century. The first English settlement in South Carolina was not until 1670. During the "War of Jenkins' Ear", 1739-1748 (I am not making the name up!), The Spanish captured Ft. St. Simons, Ga with a fleet of 36 ships. They also burned the fledgling Scottish settlement at what is now Beaufort, SC. In fact, English trade from South Carolina was brought to a virtual standstill during this period by the presence of Spanish privateers who openly anchored in Port Royal and St. Helena Sounds. There are many references to this in a very early English newspaper called The South Carolina Gazette. The Spanish actively opposed English Colonial efforts in SC until the 1740's. Two other reasons Spanish vessels would have chosen to sail into the waters of Georgia and South Carolina: information and control. The Spanish Crown craved both. And of course, there is the Gulf Stream. There are seasonal variations, but it flows NE from the Georgia/Florida border. Coupled with the fact that the South Carolina coast also runs NE, following the stream would put ships off the coast of SC for a considerable distance. A bold Admiral in a hurry might ride it all the way past Cape Hatteras...