From reading this post, it appears that the forecast for La Nina to develop later this year is based on how surface temperatures in the equatorial Pacific are starting to cool, how there is a large and growing pool of cooler-than-normal water below the surface in the equatorial Pacific, and how a bit more than half of strong El Ninos since 1950 have been followed within a few months by La Nina (which Michelle L'Heureux also cited in her response to Bailey's response), even though conditions in the Pacific during the spring make it hard to predict what phase ENSO will be in later in the year. 

Is all of this correct?  As well, what other factors are at play that strengthen this conclusion?  And, what factors are at play that weaken confidence in this prediction?