My NC had a similar minor problem a few years ago when parked at Gatwick for a fortnight, with the slightly salty damp rear discs exposed to sustained heavy weather against the driver’s side, aggravated a month later by a third week equally bad. Fortunately a friend has a lathe big enough to clean off the rust as shown in my previous post below. Not much metal needed to be removed, but it was more than the pads could manage.
Since then if I know the weather is going to be bad I take along some wheel covers. They really do work a treat.