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

For the week ending 1 January 2017, sea surface temperatures (SSTs) in the equatorial Pacific Ocean are close to average, clearly within the ENSO-neutral range. The past fortnight has seen a slight warming across the equatorial Pacific, and notable cooling of warm anomalies off northwest Australia, likely associated with the southward progression of the monsoon. Off southeast Australia, weekly sea surface temperature anomalies have increased to more than 2 °C above average.

The El Niño–Southern Oscillation (ENSO) remains neutral—neither El Niño nor La Niña. All but one of the climate models surveyed by the Bureau indicate neutral conditions are likely to persist until at least early in the southern autumn. When ENSO is neutral, weather patterns over the Pacific region are typically close to normal. This means there is a lower likelihood that eastern Australia's climate will be considerably wetter or drier than normal.

Although almost all ENSO indicators are firmly within their neutral range, cloud and rainfall patterns continue to show some weak La Niña-like characteristics. However, the central tropical Pacific Ocean has warmed in recent weeks, and further warming is expected in the coming months, suggesting cloud patterns are likely to return to normal during the southern summer. Similarly, warm waters in the eastern Indian Ocean have cooled considerably in recent weeks, with the onset of the southern monsoon, and hence cloud patterns have eased closer to normal.

The Indian Ocean Dipole has little influence on Australian climate during the months of December to April.

Cloudiness near the Date Line remains below average, and has been generally below average since the start of August.

Equatorial cloudiness near the Date Line typically increases during El Niño (below average OLR) and decreases during La Niña (above average OLR).

Trade winds for the 5 days ending 1 January 2017 were close to average. Trade winds have broadly remained close to average since the end of the 2015-16 El Niño in autumn 2016.

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, or even reversal, of the trade winds.

Climate models surveyed by the Bureau indicate that neutral ENSO conditions are likely for the remainder of the southern hemisphere summer and into autumn.

Only one of the eight models surveyed continues to indicate an increased likelihood of the central tropical Pacific Ocean exceeding La Niña thresholds—but for too short a time to be considered an event—before warming. All models indicate the central Pacific is likely to warm over the coming months.

Most models maintain neutral outlooks through to at least May 2017; however, one model suggests strong warming may be possible in autumn, reaching El Niño thresholds in May. It must be noted that this outlook straddles the autumn predictability barrier—typically the ENSO transition period—during which most models have their lowest forecast accuracy.

SST anomalies for December show the equatorial Pacific Ocean is close to average (within 0.5 °C of the long-term average). Only a few small areas remain cooler than −0.5 °C. A band of weakly warmer-than-average water persists in the southwest Pacific, close to the South Pacific Convergence Zone (SPCZ).

Warmer waters persist in the far western equatorial Pacific, but have cooled over the past few months. Only a small area off the northwest coast of Australia is more than +1 °C warmer than average, and also an area to the east of the Asian continent. Waters off the east coast of southeast Australia also remain warmer than average.

The December values for the NINO3, NINO3.4 and NINO4 regions were −0.3 °C, −0.3 °C and 0 °C, respectively.

The 30-day Southern Oscillation Index (SOI) to 1 January 2017 is +4.0 (90 day value −0.1), which is within the neutral ENSO range. SOI values have been within the neutral range since mid-October.

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

The Indian Ocean Dipole (IOD) is neutral. The weekly index value to 1 January is −0.23 °C.

The May outlook suggests a neutral IOD for the end of autumn.

The influence of the IOD on Australian climate is weak during December to April. This is because the monsoon trough shifts south over the tropical Indian Ocean, changing wind patterns, preventing an IOD ocean temperature pattern from being able to form.

The four-month sequence of sub-surface temperature anomalies (to December) shows cooler than average water across the sub-surface of the central to eastern equatorial Pacific Ocean. This cooler water has been progressively warming and shrinking in volume since September.

Weak warm anomalies have persisted in the top 100 metres of the tropical Pacific in areas west of the Date Line. December saw an increase in intensity of these weak warm anomalies, which are now approximately +2 °C.

The sub-surface temperature map for the 5 days ending 1 January 2017 shows waters are close to average across the sub-surface of the equatorial Pacific. Weak warm anomalies emerged in the western Pacific sub-surface late last year, and are slowly moving towards the central Pacific sub-surface. These warmer waters are up to 2 °C above average.