Synopsis: La Niña is favored to develop during August - October 2016, with about a
55-60% chance of La Niña during the fall and winter 2016-17.
ENSO-neutral conditions were observed during the past month, as indicated by near-to-below average surface temperatures (SST) across the eastern equatorial Pacific Ocean. While the Niño-4 region was slightly above average, the other Niño indices were either slightly below average or near zero during June. Below-average subsurface temperatures continued and extended to the surface in parts of the central and eastern equatorial Pacific. Atmospheric anomalies over the tropical Pacific Ocean also indicated ENSO-neutral conditions. The traditional Southern Oscillation index was slightly positive while the equatorial Southern Oscillation index was near zero. The upper and lower-level winds were both near average across most of the tropical Pacific. Convection was slightly suppressed over portions of the western tropical Pacific and enhanced over part of Indonesia. Collectively, these atmospheric and oceanic anomalies reflect ENSO-neutral conditions.
Many models favor La Niña (3-month average Niño-3.4 index less than or equal to -0.5°C) by the end of the Northern Hemisphere summer, continuing during fall and lasting into winter. Statistical models predict a later onset time (i.e., mid-fall) than dynamical models, and also predict a relatively weaker event. The forecaster consensus is somewhat of a compromise between the two model types, favoring La Niña onset during the August-October season, and predicting a weak event (Niño-3.4 index between -0.5°C and -1.0°C), if an event were to form. Overall, ENSO-neutral conditions currently prevail and La Niña is favored to develop by August - October 2016, with about a 55-60% chance of La Niña during the fall and winter 2016-17.
September is typically a key month for Arctic sea ice as it represents the least extent and concentration for the season. The interpretation of the anomaly is against the historical sea ice concentration map. Therefore a September forecast for an anomaly of 40 to 50 maybe again an area that historically has a concentration of 70 - 80 percent. The forecast for such an area would be between 28 and 40 percent.
Overall sea ice concentrations for the Arctic for September are well below normal for much of the region with only isolated areas with greater concentrations in the Russian zone and northeast of Greenland.