Hi Ashok,

As Nathaniel noted in the comment above, NOAA issues a La Nina Advisory when recent conditions satisfy La Nina conditions, and the expectation is that these conditions will persist long enough to satisfy the duration requirement. So the question is not whether ASO qualified as a La Nina but if scientists believe La Nina conditions are present in the ocean and atmosphere and that those conditions will last long enough (5 consecutive three-month periods) to qualify using the standard definition. 

This brings up another important point about why we issue La Nina Advisories now. The 5-consecutive three month period definition is one applied after the event is over. For the public to prepare for an event, there needs to be an advisory that does not wait that long. This is where the La Nina advisory fits in. We would not issue a La Nina advisory if we did not think that it would fulfill the historical, 5-consecutive three month period of SST's below -0.5C.