Since you're already getting bubbling, rust is forming under the paint. At this point, the only way to really repair it is to sand down to bare metal, properly prep the surface, and repaint. It is possible to feather this in and make it look decent, but it's pretty easy to remove the hood and paint the entire hood. You'd probably not find any body shop that is proud of the work they do to agree to do spot repairs, they'll want to repaint the entire hood.
Depending on how bad the bubbling is, the corrosion could be pretty deep already and require some filler or possibly even a new hood to make it look right.
-Rod