Weekly Tropical Climate Note

Issued 30 June 2015

Madden–Julian Oscillation strengthens over western Pacific region

During the last week, the Madden–Julian Oscillation (MJO) strengthened as it moved over the eastern Maritime Continent, where it enhanced convection and increased local rainfall. The MJO has now moved into the western Pacific region where all international models expect it to strengthen over the next week. In the wake of the MJO, the southwest Indian monsoon has eased in the last few days, apart from the east and northeast where it remains active.

In combination with other tropical waves, the MJO has generated areas of significant weather over the western Pacific region—both north and south of the equator—which have the potential to develop into a tropical cyclone in the coming days. Tropical cyclone formation in the southern hemisphere in this region is rare in June and unprecedented in July (since reliable satellite records became available).

Historically, when the MJO moves over western Pacific longitudes at this time of the year, the southeast trade winds become weaker than normal over northern Australia. This can increase the likelihood of above-average rainfall over the centralwest of Western Australia and western New South Wales, but reduce the likelihood of above-average rainfall for coastal Queensland. There is no significant rainfall trend for far-northern parts of the continent in this climatic scenario.

See the Bureau's MJO Monitoring for current MJO information.

El Niño persists in tropical Pacific

After a series of recent short-term fluctuations in the Southern Oscillation Index (SOI), the index has shown a return to negative values. The 30-day SOI value to 28 June is −9.0, while the 90-day SOI is −9.3.

Oceanic and cloud indices are consistent with El Niño, with sea surface temperatures (SST) well above El Niño levels across the equatorial eastern and central Pacific Ocean, and enhanced convection apparent near the International Date Line.

International climate models surveyed by the Bureau indicate sea surface temperatures will remain well above El Niño thresholds at least til the end of the year. The latest weekly NINO3.4 sea surface temperature anomaly is +1.3 °C.

See the Bureau of Meteorology's ENSO Wrap-Up for official El Niño information.

Next update expected by 7 July 2015 | Product Code IDCKGEW000

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