NOT SO GREEN | El Niño and La Niña
NOAA Operational Definitions for El Niño and La Niña
El Niño: characterized by a positive ONI ( Oceanic Niño Index ) greater than or equal to + 0.5 ºC. La Niña: characterized by a negative ONI less than or equal to - 0.5 ºC. By historical standards, to be classified as a full-fledged El Niño or La Niña episode, these thresholds must be exceeded for a period of at least 5 consecutive overlapping 3-month seasons.
Discussion and comparison of recent conditions with historic El Niño conditions
Positive SST anomalies cover much of the off-equatorial tropical Pacific, but cold anomalies are present right along the Equator from 120W to the dateline, as seen in the latest weekly SST map. The cold anomalies look more focused on the Niño 3.4 SST region than last month.
For an alternate interpretation of the current situation, I recommend reading the NOAA ENSO Advisory which represents the official and most recent Climate Prediction Center opinion on this subject. In its latest update ( 8 September 2016 ), ENSO-neutral conditions were diagnosed and their La Niña watch has been pulled in favor of anticipating ENSO-neutral conditions during the next six months ( at 55-60% odds ). Given my discussion above, ENSO-neutral is probably a safer bet than La Niña for now.