There will not be updates on this particular forecast based on regression. But each month the Climate Prediction Center issues another forecast for the coming ENSO conditions out to about 10 months in advance, and at the time I'm writing this (middle February), those ENSO outlooks go out to Oct-Nov-Dec 2016, which should be plenty of time to capture the possible La Nina development. The link to their latest forecasts is given in the last footnote in this blog. Right now, they actually do show a 50% chance for La Nina development for Oct-Nov-Dec 2016, somewhat in agreement with the regression forecast given above.

As for studies of big storms like Mitch and other high impact events, there have been studies related them to the ENSO condition. I am not in a position right now to name more than one, but there are many, and you would need to probe into the scientific literature about ENSO and such big weather events. The one article I do know is the following: Authors: Lisa Goddard and Maxx Dilley: "El Nino: Catastrophe or Opportunity?" Journal of Climate, Volume 18 (March 2005), pages 651–665.