I am not an expert or anything but here is what i think is happening.. hehe
I think it "might cause" cause it clearly states: COLOUR CODE: NIL ERUPTION DETAILS: EXPLODED AT 20120410/2007Z VA CLD UNKNOWN : So volcanic cloud unknown and as it is written it is still not identifiable... but it is to be "aware"
but untill +6 +12 +18 they dont expect it. but you will have to wait if volcanic ash is surely detected on IM.
I dont know if I am saying it right.. correct me if wrong..
best regards,