Synopsis: A transition to ENSO-neutral is expected to occur by February 2017, with ENSO-neutral then continuing through the first half of 2017.
La Niña continued during December, with negative sea surface temperature (SST) anomalies continuing across the central and eastern equatorial Pacific. The weekly Niño index values fluctuated during the last month, with the Niño-3 and Niño-3.4 regions hovering near and slightly warmer than -0.5°C. The upper-ocean heat content anomaly was near zero when averaged across the eastern Pacific, though near-to-below average subsurface temperatures were evident closer to the surface. Atmospheric convection remained suppressed over the central tropical Pacific and enhanced over Indonesia. The low-level easterly winds were slightly enhanced over the western Pacific, and upper-level westerly anomalies were observed across the eastern Pacific. Overall, the ocean and atmosphere system remained consistent with a weak La Niña.
The multi-model averages favor an imminent transition to ENSO-neutral (3-month average Niño-3.4 index between -0.5°C and 0.5°C), with ENSO-neutral lasting through August-October (ASO) 2017. Along with the model forecasts, the decay of the subsurface temperature anomalies and marginally cool conditions at and near the ocean surface portends the return of ENSO-neutral over the next month. In summary, a transition to ENSO-neutral is expected to occur by February 2017, with ENSO-neutral then continuing through the first half of 2017.
Even as the tropical Pacific Ocean returns to ENSO-neutral conditions, the atmospheric impacts from La Niña could persist during the upcoming months.
All of mainland Southeast Asia should be slightly to moderately warmer than normal except for the Mekong delta region that should be slightly cooler than normal. Much of insular Southeast Asia should be near normal to slightly warmer than normal.
Most of mainland Southeast Asia should be near normal in what is typically already a relatively dry month. Coastal and Central Vietnam should be slightly drier than normal along with northern Thailand and Myanmar. Much of insular Southeast Asia should be near normal with slightly drier conditions in Java and western Borneo and the Central Philippines and West Papua and northwestern Sulawesi.