Central banks in the US and Europe likely will implement "several rounds" of monetary easing programs in November, but with uncertain chances of success, Pimco co-CEO Mohamed El-Erian told CNBC.

Pimco co-CEO Mohamed El-Erian

The first leg of such programs—known in market vernacular as "quantitative easing," or QE—was somewhat effective but largely a disappointment, he said. (Click here for an explanation of QE.)