Is El Niño a tropical disturbance?
Answer is both yes and no.
Yes, El Nino is an aberrant climatic condition that develops over tropical pacific region. Ocean surface becomes unusually warm during December.
No, because El Nino causes unusual warmer winter conditions in subtropical regions of north America.
Though its true that el nino causes more number of tropical cyclones but that is only one of the many global events associated with el nino.
There is erratic temperature and rainfall in different parts of the world during the years affected by el nino. Generally el nino adversely affects southwest monsoon in Indian subcontinent; overall, there is less rainfall in whole of Australasian region.
There is a similar and opposite event of el nino, termed la nina.