Hiroshima is debated. Some say 12.5kt while other's day 15kt. Most historians now go with 12.5kt as the more accurate yield. Nagasaki and Trinity were in the 20-22kt range.
30 Kilotons at 500ft to 1500ft would be devastating. Even a ground burst would be very destructive.
That said, I still have serious doubts about these kinds of stories not only because of what I know about nuclear weapons but because the same stories (with minor variations) have appeared every year since Sept. 11th.
I agree it is one of those stories that seems to have a cycle. What concerns me is that the "missing" Soviet era nukes have been on the pipeline for about 15 years. It does seem that somebody would of at least tried to use one by now. The other thing that bothers me is that you can't swing a dead cat in the mercenary world without hitting a Russian.
Hiroshima may have seemed bigger because as I recall it is in kind of a bowl geographically.