Such eruptions do come after extended periods of global warming which also vaporises a lot of water into the atmosphere. The eruptions are occasioned by increased pressure on the crust from expanding gases and molten lava due to excess heat inside the planet.
El Nino has largely been presented as a consequence of some mysterious processes in the Pacific Ocean leading to warming of ocean waters, pollution of the sea bottom resulting in deaths of marine life among other things. But Pacific is home to the ‘Ring of fire’ and is the most active submarine volcanic region in the world. When a volcano erupts under the sea, we expect what we see in terrestrial volcanic eruptions to happen and must also imagine the implications under water.
During volcanic eruptions hot lava and gases are discharged from inner earth into outer space. Under water, hot lava will still be discharged though it can’t be sustained much longer because of water’s cooling capacity. Volcanic dust and gases discharged under water will result in pollution and warming of ocean waters because they come out hot and are toxic. Any small decline in pressure inside the vents will allow sea water to rush into the volcano causing further cooling.
El Nino does not depend on Pacific submarine eruptions alone but it is important to remember that being very active, the ring of fire will rarely miss an opportunity to erupt when other volcanoes are erupting. A Google search on the number of volcanic eruptions in the periods immediately before El Ninos will vindicate the fact of the relationship between volcanic activities and El Ninos. The reason for this relationship is that such eruptions allow the planet to loose some of its heat therefore increasing its condensing capacity especially at a time when excess vapour exists in the atmosphere.

Is it possible to predict El Nino with exactitude?
Having looked at what causes El Nino, we can proceed to examine what it entails to predict its occurrence. Two conditions have been identified as prerequisite for its occurrence and these are;
1) Extended periods of global warming leading to vaporisation of excess water into the atmosphere, and
2) Abrupt reduction in global temperatures allowing for increased condensing capacity of the atmosphere for a continued period of time and such is occasioned by volcanic eruptions.
Global warming has persisted in recent years with record breaking warm temperatures being registered across different regions around the world. So the first condition has been met and any reduction in atmospheric temperatures is certain to result in excessive rainfall synonymous with flash floods which have characterised many regions across the planet in recent times. But it is not possible to predict that there will be high magnitude volcanic eruption in August or a series of volcanic eruptions around August leading to El Nino. Though it would be proper to predict that El Nino is in the offing because the crust cannot withstand the pressure forever before it gives in through eruptions. The exact onset for El Nino can not be predicted because we have not established the rate at which heat and pressure beneath the crust increase nor have we established the strength of the crust at its weakest point to be able to state at which point in time the pressure will crack the crust.

What happens in August?
August is a summer month for the northern hemisphere and for the sub-tropical north it is the time when rainfall is usually experienced. With global warming having vaporised and continuing to vaporize more water into the atmosphere, it is certain there will be abundant vapour to be condensed into rainfall when the right conditions obtain resulting in high amounts of rainfall leading to widespread flooding in the affected regions. But would the above normal rainfall expected constitute flash floods or El Nino?