We will see.... at this point we're still anticipating westerly wind anomalies to shift eastward in the next week or so and warm the surface somewhat. In the last week we noticed Nino-3.4 go from 0.5C to 0.7C so some of that anticipation is playing out.  We also notice continued coupling in convection with dry conditions over Indonesia and wetter conditions near the Date Line.  Our probabilities indicate El Nino is likely in the summer, with probabilities diminishing as we get into the fall/winter, which imply more uncertainty in the outcomes.  

BOM uses a different threshold for El Nino, so they require a stronger event to declare.  This is certainly not the first time NOAA has declared an event and BOM has not.