Sea surface temperature (SST) anomalies continued to cool across the tropical Pacific Ocean during December. The sea surface temperature (SST) anomaly map for December shows cool anomalies have increased in the central Pacific near the dateline when compared to November; sea surface temperatures more than 1 °C cooler than normal cover areas of the central and eastern equatorial Pacific.

Index November December Temperature change NINO3 −0.8 −0.6 0.2 °C warmer NINO3.4 −0.9 −0.8 0.1 °C warmer NINO4 −0.5 −0.8 0.3 °C cooler

During the past two weeks, sea surface temperature anomalies have in the central equatorial Pacific have cooled, reversing the recent warming trend. The SST anomaly map for the week ending 29 January shows cool anomalies present across most of the central equatorial Pacific, with a large part of this area more than 1 °C cooler than normal for this time of the year.

Index Previous Current Temperature change (2 weeks) NINO3 −0.4 −0.5 0.1 °C cooler NINO3.4 −0.8 −1.0 0.2 °C cooler NINO4 −0.9 −1.0 0.1 °C cooler

An animation of recent SST changes | Weekly data graph

The volume of cooler than average water in the sub-surface of the eastern tropical Pacific has shrunk over the past two weeks. The map for the 5 days ending 30 January shows a volume of water more than 4 °C cooler than usual for this time of the year remains in the sub-surface. Warm anomalies in the sub-surface of the western tropical Pacific have also shown a significant increase, with a much larger volume of water more than 3 °C warmer than usual, for this time of the year as compared to two weeks ago.

Animation of recent sub-surface changes | Archive of sub-surface temperature charts

The Southern Oscillation Index (SOI) continued to drop over the past fortnight, but remains above La Niña thresholds. The latest (30 January) 30-day SOI value is +10.3.

Sustained positive values of the SOI above +8 may indicate a La Niña event, while sustained negative values below −8 may indicate an El Niño event. Values of between about +8 and −8 generally indicate neutral conditions.

Monthly_graph | SOI table | SOI text

Trade winds have in the central and western tropical Pacific strengthened marginally, when compared with two weeks ago. The latest wind anomaly map, for the 5 days ending 30 January, shows trade winds continue to be stronger than average across most of the equatorial Pacific, but near-neutral in the eastern Pacific.

During La Niña events, there is a sustained strengthening of the trade winds across much of the tropical Pacific, while during El Niño events there is a sustained weakening of the trade winds.

Cloudiness near the dateline has remained suppressed over the past two weeks.

Cloudiness along the equator, near the dateline, is an important indicator of ENSO conditions, as it typically increases (negative OLR anomalies) near and to the east of the Date Line during an El Niño event and decreases (positive OLR anomalies) during a La Niña event.

The majority of outlooks from leading international climate models surveyed by the Bureau indicate that the current La Niña will decline over the coming weeks. The current event is expected to persist through the remainder of summer, but neutral values are forecast for the coming autumn.

The Indian Ocean Dipole (IOD) typically has little influence in Australia over summer. The IOD index is currently neutral; the index value for the week ending 29 January was 0.0.

Recent forecasts from the POAMA model predict neutral IOD conditions for the remainder of summer and the following autumn.

IOD time series IOD map IOD forecasts DMI values