Issued on Tuesday 21 May 2013 | Product Code IDCKGEWWOO
The tropical Pacific has remained neutral with respect to the El Niño-Southern Oscillation (ENSO) since mid-2012. All atmospheric and oceanic indicators of ENSO are currently well within neutral values. Weekly sea surface temperatures across the eastern half of the tropical Pacific have cooled slightly over the past month, but remain within neutral territory. International climate models surveyed by the Bureau of Meteorology suggest the tropical Pacific will remain ENSO-neutral through the southern hemisphere winter.
The Indian Ocean Dipole (IOD) is currently neutral. Model outlooks of the IOD are becoming more consistent, with four of the five models surveyed now favouring the development of a negative IOD during the southern winter-spring period. The fifth model is also suggesting values on the negative side of neutral. A negative IOD during winter-spring increases the chances of above-normal rainfall over southern Australia.
Next update expected on 4 June 2013 | print version
The sea-surface temperature (SST) anomaly map for April shows near-average SSTs across nearly the entire tropical Pacific. A small area of cool anomalies hugs the South American coastline and warm anomalies continue across most of the Maritime Continent region. The eastern equatorial Pacific has cooled compared to April but elsewhere anomalies remain similar.
SST anomalies have cooled in the eastern equatorial Pacific when compared to two weeks ago. The map for the week ending 19 May shows negative SST anomalies are present along the equator between the South American coast and 140°W. Elsewhere along the equator SSTs are near average with warm anomalies in the far western Pacific and across the south of the Pacific Basin, poleward of the tropics. Warm anomalies also remain around much of the Australian coastline.
|The four-month sequence of sub-surface temperature anomalies (to 20 May) shows cool anomalies in the sub-surface of the eastern to central equatorial Pacific; this pool of cooler than normal water peaked in extent in January and has weakened since. A small area of this pool of cooler-than-average water is more than 3 °C cooler than average for May. Warm anomalies remain present in the sub-surface of the far western equatorial Pacific.|
|Anomalies in the subsurface of the equatorial Pacific remain similar to those from two weeks ago. The sub-surface map for the 5 days ending 20 May shows anomalies more than 1 °C cooler than average are present between 50 and 250 m deep across nearly all of the equatorial Pacific, reaching more than 3 °C cooler than average east of the Date Line. Warm anomalies are still present in the far western equatorial Pacific sub-surface.|
The Southern Oscillation Index (SOI) has risen over the last two weeks and remains neutral. The latest 30-day SOI value to 19 May is +1.6.
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.
Trade winds have weakened slightly in the far western tropical Pacific during the past two weeks. The anomaly map for the 5 days ending 19 May shows trade winds remain stronger than average across the far western tropical Pacific and near average elsewhere.
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 Date Line has been near average during the past two weeks.
Cloudiness along the equator, near the Date Line, 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.
International climate models surveyed by the Bureau indicate that SSTs in the equatorial Pacific Ocean are likely to remain neutral at least until the southern hemisphere spring.
The Indian Ocean Dipole (IOD) is currently neutral, with the latest IOD index value at −0.6 °C for the week ending 19 May. Current model outlooks indicate an enhanced likelihood of a negative IOD event developing in either the southern hemisphere winter or spring. Four of the five models surveyed indicate a negative IOD event, while the fifth indicates weaker negative values of the index. A negative IOD during spring increases the chances of above-average rainfall over southern Australia.