I would say that it is either frog-eye leafspot (Cercospora nicotianae) or brown spot (Alternaria alternata). Both are fungal. The fungi grow during wet periods, then sporulate and spread to upper leaves during dry periods. There is not much you can do, other than avoid that variety in that soil during subsequent seasons. The brown areas will dry and leave a hole or a white spot during color-curing. Some tobacco varieties are more resistant than others.
Bob