The National Weather Service has announced weak El Nino conditions now exist and there is a 50-60% chance it will continue through the Northern Hemisphere summer of 2015.
I have been following the El Nino - Southern Oscillation (ENSO) conditions closely since last spring when it began to look as though the ENSO conditions might come to pass. There are some areas in the equatorial Pacific that are monitored closely - Area 1+2 - located near South America; Area 3- located a little further out; Area 4- located even further west; and Area 3.4, which overlaps areas 3 and 4. It is 3.4, essentially in the middle of the Pacific Ocean, they pay most attention to and is specifically mentioned in the NWS announcement.
At least twice in the last year I thought the ENSO had begun, once in the late spring and once in the fall. In addition to the borderline conditions there were also weak weather patterns consistent with it occurring. Each of those times the conditions came apart, though. My guess is the mechanisms responsible for causing this event (and it is very complicated) were getting close to coming together, but not quite.
So, what does this mean for worldwide weather and the climate? My guess right now (a fool's errand) is that it won't have a very large impact. It looks as though it is a weak system and any impact will be small.
Significantly, it is not likely this system will do much for the California drought. Instead, the data indicate the snowpack in the Sierra Nevada mountains is dangerously low, meaning California will have another terrible summer. Statewide, the snowpack is measured at just 19 percent of the long term average. A weak El Nino will not change that.
According to the NWS, some areas of the planet may see some light affects from this El Nino, but worldwide effects are not expected. How all of this ties together is something for scientists to study and figure out. While I follow it, I am not involved in any kind of research on ENSO so I can't state what this on-again/off-again cycle means. Hopefully, though, it is one more piece of the puzzle to help us figure out this very important system in our climate.