Climate Driver Update history
Climate drivers in the Pacific, Indian and Southern oceans and the Tropics

Sea surface temperature (SST) anomalies in the tropical Pacific Ocean remain warmer than average along most of the equator, and are close to average across parts of the Maritime Continent.

SSTs are also warmer than average in a broad band across the southern Pacific extending from around the Date Line to south of 30°S in the east; the opposite of what is expected in a typical El Niño.

SSTs for the three NINO regions have cooled slightly compared to two weeks ago, and while still warm, are within the ENSO neutral range. The latest values of the key NINO indices in the tropical Pacific for the week ending 20 January are: NINO3 +0.5 °C, NINO3.4 +0.4 °C and NINO4 +0.7 °C.

Persistent NINO3 or NINO3.4 values warmer than +0.8 °C are typical of El Niño, while persistent values cooler than −0.8 °C typically indicate La Niña.

Around Australia, SSTs are warmer than average across the Great Australian Bight, extending southwest of Tasmania and across Bass Strait and the Tasman Sea, and also along the New South Wales coast. SSTs are more than two degrees warmer than average across most of the area between Australia and New Zealand.

Elsewhere around Australia SSTs are generally close to average temperatures.

Recent observations and climate model outlooks suggest the immediate risk of El Niño has passed.

However, there remains an increased likelihood that El Niño will develop later in 2019. The Bureau's ENSO Outlook has therefore moved to El Niño WATCH, meaning there is approximately a 50% chance of El Niño developing during the southern hemisphere autumn or winter.

Tropical Pacific sea surface and sub-surface temperatures remain warmer than average, but since late 2018 they have cooled from El Niño-like values towards ENSO-neutral values. Atmospheric indicators such as cloudiness, trade winds and the Southern Oscillation Index all continue to generally remain within the ENSO-neutral range.

While most climate models indicate ENSO-neutral conditions for the immediate future, the current ocean warmth and likelihood of ongoing warmer than average conditions mean the risk of El Niño remains. Three of eight models suggest that El Niño may establish by mid-2019.

The Indian Ocean Dipole (IOD) is neutral. The IOD typically has little influence on Australian climate from December to April.

Cloudiness near the Date Line has generally been near average or above average since early December. It would typically be well above average during El Niño.

Equatorial cloudiness near the Date Line typically increases during El Niño (negative OLR anomalies) and decreases during La Niña (positive OLR anomalies).

Trade winds were near average across the equatorial Pacific for the 5 days ending 20 January.

During El Niño there is a sustained weakening, or even reversal, of the trade winds across much of the tropical Pacific. Conversely, during La Niña, there is a sustained strengthening of the trade winds.

The lack of an El Niño-like wind pattern indicates the atmospheric circulation required for El Niño has been missing this summer (also see SOI and Cloudiness sections).

Outlooks from the eight surveyed climate models have backed off over recent weeks. Three models predict sea surface temperatures (SSTs) will be above El Niño thresholds during February, while the rest indicate warm but ENSO-neutral SSTs.

The seasonal cycle of ENSO typically favours a decay of the east to west difference in SSTs across the tropical Pacific during summer to autumn.

Outlooks remain mixed during the southern hemisphere autumn to winter. It should be noted that model accuracy forecasting through the autumn months is lower than at other times of the year, and this may explain the wider-than-usual spread in model outlooks for the coming months.

Some models anticipate a continued decline in SSTs over autumn and early winter, however half see a renewed warming. The degree of warming anticipated varies across those models. For June, three of the eight models predict SSTs will be above El Niño thresholds, with another three on the warm side of neutral.

Sea surface temperatures (SSTs) for December were warmer than average for much of the tropical Pacific Ocean, and much of the southern Pacific.

The December values for NINO3 were +0.8 °C, NINO3.4 +0.8 °C, and NINO4 +0.9 °C.

The 30-day Southern Oscillation Index (SOI) to 20 January was −0.1, and the 90-day SOI was +3.0.

Sustained negative values of the SOI below −7 typically indicate El Niño while sustained positive values above +7 typically indicate La Niña. Values between +7 and −7 generally indicate neutral conditions.

During the southern hemisphere summer the SOI can be more volatile due to the passage of tropical storms and should therefore be viewed with caution. However, the lack of a clear, sustained El Niño signal in the SOI indicates the atmospheric circulation required for El Niño has been missing this summer (also see Trade Winds and Cloudiness sections). This coupling of atmospheric circulation and ocean temperature patterns is the mechanism which reinforces and sustains El Niño, and facilitates widespread shifts in Australian and global weather and climate.

The Indian Ocean Dipole (IOD) is currently neutral. The latest weekly index value to 20 January was +0.02 °C.

Due to the movement of the monsoon trough in the Indian Ocean, the IOD typically has little influence on Australian climate from December to April. When the monsoon trough shifts southwards into the southern hemisphere, it changes the broadscale wind patterns, meaning that the IOD pattern is unable to form.

All of the six international climate models surveyed by the Bureau indicate that the IOD will remain neutral through autumn 2019.

The four-month sequence of sub-surface temperature anomalies (to 21 January) shows warm anomalies across most of the top 200 m of the western half of the equatorial Pacific sub-surface, and cool anomalies in the sub-surface of the eastern half, rising from about 150 m depth in the centre, to just below the surface in the very east of the basin.

Warm anomalies in the sub-surface have decayed over late 2018 and early 2019, although small parts of the sub-surface to the west of the Date Line remain more than two and a half degrees warmer than average.

Temperatures for the five days ending 20 January show warmer than average waters around and just east of the Date Line between about 100 m and 200 m depth in the equatorial Pacific. Warm anomalies in this region reach more than three degrees above average. Weak warm anomalies are present in the shallow eastern equatorial Pacific sub-surface above 100 m.

Waters across the sub-surface have shifted further towards average temperatures over the past two weeks.