One problem with volcanic activity is trouble that is caused by the ash. The ash can cause flights to be canceled (as has already happened) and the particles in the ash can damage car paint, etc. So, to help people cope, the Japan Meteorological Agency has started to issue predictions of areas that will be affected by the stuff. Unfortunately, I think the information is only available in Japanese:
http://www.data.jma.go.jp/svd/vois/data/tokyo/STOCK/kouhai/kouhai.html
They don’t issue reports every day. I assume that the reports are only issued when the ash is expected to cause significant problems.