ENSO Wrap-Up
Current state of the Pacific and Indian Ocean

Weekly sea surface temperatures

Graphs of the table values

Monthly sea surface temperatures

Graphs of the table values

5-day sub-surface temperatures

Monthly temperatures

Southern Oscillation Index

30-day SOI values for the past two years
Select to see full-size map of 30-day Southern Oscillation Index values for the past two years, updated daily.

Trade winds

5-day SST and wind anomaly from TAO/TRITON
Select to see full-size map of 5-day SST and wind anomaly from TAO/TRITON.

Cloudiness near the Date Line

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ENSO outlooks

NINO3.4 SST plumes from Bureau model forecasts, updated daily
Select to see full-size map of NINIO3.4 SST plumes from Bureau model forecasts, updated daily.

Indian Ocean Dipole outlooks

IOD SST plumes from Bureau model forecasts, updated daily
Select to see full-size map of IOD SST plumes from Bureau model forecasts, updated daily.

For the week ending 8 October, sea surface temperatures (SSTs) were cooler than average in the eastern half of the equatorial Pacific Ocean to the south of the equator and along the coast of South America. However, to the north of the equator in the eastern equatorial Pacific, SSTs were warmer than average. This region has seen a significant warming of SSTs over the past two weeks, disrupting the cooling trend seen since mid-winter.

Anomalies along the remainder of the equator are generally near average.

Weak warm anomalies persist across much of the western Pacific, in both the north and south of the basin, and in the central Pacific north of the equator. Stronger warm anomalies extend across most of the area between Indonesia, Vietnam, and Japan, and along large parts of the east coast of Australia.

All of NINO3, NINO3.4, and NINO4 have warmed during the past fortnight, with NINO3 warming by 0.4 ºC. Latest weekly values for the week ending 8 October are: NINO3 0.0 °C, NINO3.4 0.0 °C, NINO4 +0.2 °C.

Persistent values below −0.8 °C are typically indicative of La Niña, while persistent values above +0.8 °C are typical of El Niño.

The El Niño–Southern Oscillation (ENSO) remains neutral. The surface of the tropical Pacific has warmed over the past fortnight as a result of weaker trade winds. This has reversed the cooling trend that had been observed since mid-winter. While sea surface temperatures remain well within the neutral range, anomalously cool water persists below the surface.

International climate models surveyed by the Bureau suggest this recent surface warming may only be temporary, with further cooling of the tropical Pacific Ocean likely. Five of the eight models suggest sea surface temperatures will reach La Niña thresholds by December 2017, but only three maintain values for long enough to be classified as a La Niña event.

While unusual, it is not unheard of to see La Niña develop this late in the year. Of the late-developing La Niña events, their effect on summer rainfall has been mixed, with some leading to widespread above-average falls across eastern Australia, and others having minimal effect. The current 3-month rainfall outlook suggests only a 50% likelihood of wetter conditions in many parts of the country.

The Indian Ocean Dipole (IOD) remains neutral. Three of the six climate models surveyed suggest positive IOD thresholds may be reached during spring, but these positive values would be short-lived as IOD events naturally decay by December.

Cloudiness near the Date Line has been generally below average (positive OLR anomalies) during September and most of August, but values over the most recent week have dipped, returning cloudiness to near-average levels.

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 8 October were slightly stronger than average over the western tropical Pacific and near average over the eastern tropical Pacific. A period of weaker trade wind strength over the tropics in the central to eastern Pacific during the past two weeks may have contributed to the return to closer to average SSTs in the region, and the stalling of the cooling trend of recent months.

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.

International climate models surveyed by the Bureau indicate that further cooling of equatorial Pacific Ocean sea surface temperatures is expected during spring and into summer. All models anticipate that SSTs may approach or surpass La Niña thresholds during spring or early summer. However, only three models indicate that these SSTs will persist long enough to be classified as a La Niña event.

Late forming La Niña are rare, but not unheard of. You can read about the evolution and effect of previous events in our La Niña Summaries.

Sea surface temperature (SST) anomalies for September show SSTs were cooler than average in the eastern equatorial Pacific Ocean. Generally weak warm anomalies were present across most of the South Pacific, the western Pacific, and the mid-latitudes of the North Pacific. Areas of stronger warm anomalies in excess of one degree above average were observed along parts of the east coast of Australia, across the Philippine Sea, and in areas of the mid- to high latitudes of the South Pacific, particularly to the east of New Zealand.

The September value for NINO3.4 was −0.3 °C, NINO3 −0.4 °C, and NINO4 +0.1 °C. All three September values cooled compared to August, but remained within the neutral range.

The 30-day Southern Oscillation Index (SOI) to 8 October is +9.1 (90-day value +6.6), having passed into the La Niña value range within the last week.

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

The Indian Ocean Dipole (IOD) is neutral. The weekly index value to 8 October was +0.05 °C.

Most of the climate models surveyed by the Bureau indicate that the IOD will remain neutral during spring. Three of the six models suggest a positive IOD remains a possibility during spring. A positive IOD is typically associated with below average spring rainfall over southern and central Australia.

IOD events typically decay during spring, and the influence of the IOD on Australian climate is weak during the months December to April. This is because the monsoon trough shifts south over the tropical Indian Ocean changing wind patterns, which prevents the IOD pattern from being able to form.

The four-month sequence of sub-surface temperature anomalies (to September) shows cool anomalies have continued to develop across most of the equatorial Pacific Ocean down to a depth of 200 m. In some areas of the central equatorial Pacific sub-surface anomalies are up to 4 degrees cooler than average for September. An area of weak warm anomalies persists in the shallow sub-surface waters of the western equatorial Pacific Ocean, but has decreased in size compared to August.

The sub-surface temperature map for the 5 days ending 9 October shows a large pool of slightly cooler than average water present in the subsurface of the central to eastern equatorial Pacific Ocean. Water temperatures around 100 to 150 m depth between about 160°W and 130°W were more than 3 degrees cooler than average. Sub-surface water temperatures were generally close to average across the top 100 m of the equatorial Pacific Ocean, and across the full column depth in the far western equatorial Pacific.

Product code: IDCKGEWW00