Prof. Nick Shay of the University of Miami says the oil in the Gulf of Mexico is stuck in a loop that will keep the oil moving around in a circle. He says the motion of water in the Gulf is not well understood.
There are blobs of oil going off in different directions, but most oil is concentrated in the northern Gulf of Mexico near ground zero. Some warm eddy currents gradually spin off and head west toward Texas and Mexico. Some may reattach.
If eddy currents reattach to the main loop, then the Florida Straights, South Florida and the Keys are hit especially hard.
Also, a hurricane can cause the plumes to rise to the surface (upwell) and hit the shore again.