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

Sea surface temperatures (SSTs) across the central Pacific Ocean remain close to average along the equator.

The latest values for the week ending 6 May are: NINO3 −0.2 °C, NINO3.4 −0.2 °C and NINO4 +0.2 °C. Persistent NINO3 or NINO3.4 values cooler than −0.8 °C typically indicate La Niña, while persistent values warmer than +0.8 °C are typical of El Niño.

Warmer than average SSTs (more than 1 °C above average) persist in areas of the South Pacific Ocean and the Tasman Sea, though sea surface temperatures in this region have been cooling over recent weeks. The surface of the Tasman Sea has been persistently warmer than average since the second half of November 2017.

To the north of Australia, weak warm SST anomalies remain across the Maritime Continent, with SSTs also more than 1 °C above average off the northwest coast of Australia.

The El Niño–Southern Oscillation (ENSO) remains neutral, with neither El Niño nor La Niña in the tropical Pacific Ocean. International models suggest it will remain neutral through at least the southern hemisphere winter.

Atmospheric and oceanic indicators of ENSO are generally at near average levels. Sea surface temperatures (SSTs) are close to the long-term average across the tropical Pacific Ocean, and waters beneath the surface are slightly warmer than average. In the atmosphere, the Southern Oscillation Index (SOI) and trade winds are both within the neutral range.

International models suggest the tropical Pacific Ocean will warm slowly over the coming months, but remain ENSO-neutral for the southern hemisphere winter. Only one of eight climate models suggest sea surface temperatures may approach El Niño thresholds by September; the rest maintain ENSO-neutral.

The Indian Ocean Dipole (IOD) is currently neutral. Half of the surveyed climate models suggest the IOD will remain neutral for winter, while the other half predict a negative IOD. However, the present above average SSTs off northwest Australia are a result of reduced cloud cover increasing solar warming. If this pattern persists, a typical negative IOD response, such as more cloud off northwest Australia, is less likely. During negative IOD events, winter–spring rainfall is typically above average over southern Australia.

Cloudiness near the Date Line has been below average since late February.

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

Trade winds for the 5 days ending 6 May are near average across the equatorial 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, or even reversal, of the trade winds.

All eight of the surveyed international climate models indicate that Pacific Ocean sea surface temperatures will remain within the ENSO-neutral range over the southern hemisphere winter.

One models indicates central equatorial Pacific sea surface temperatures may approach El Niño threshold values during spring, however model outlooks produced during or spanning autumn have a lower accuracy than at other times of the year, and should be viewed with some caution.

Sea surface temperature (SST) anomalies for April show SSTs were slightly cooler than average in the central and eastern tropical Pacific Ocean, although cool anomalies in this region have weakened compared to last month. Warm anomalies were present across most of the South Pacific around and south of 30°S, much of the Maritime Continent, to the west of Japan, and from the east of Mexico across the mid-latitudes of the central North Pacific Ocean.

The April value for NINO3 was −0.2 °C, NINO3.4 −0.3 °C, and NINO4 +0.1 °C.

The 30-day Southern Oscillation Index (SOI) to 6 May was −2.6, and the 90-day SOI +4.0; both well within the neutral range.

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 currently neutral. The weekly index value to 6 May was 0.00 °C.

Three of the six international climate models surveyed by the Bureau anticipate that the IOD will become negative IOD during the southern hemisphere winter, and remain so into spring. A negative IOD during winter tends to enhance rainfall across southern Australia.

It should be noted that outlook skill is lower at this time of year.

The four-month sequence of sub-surface temperature anomalies (to April) shows that the central and eastern equatorial Pacific Ocean has slowly warmed over the past three months. A pool of warmer than average water is present between 140°E and 120°W across the top 200 m of the Pacific, with weak cool anomalies in the shallow sub-surface of the eastern equatorial Pacific. Eastward propagation of warm sub-surface anomalies, as seen in recent months, is a typical feature of a decaying La Niña.

Sub-surface temperatures for the 5 days ending 6 May show a pool of slightly warmer than average water persists beetween about 100 m and 150 m depth, extending across most of the equatorial Pacific. Temperatures in most of the top 100 m and below 150 m depth are near average for this time of the year.