THE tropical Pacific ocean and atmosphere are reinforcing each other, maintaining a strong El Niño that is likely to persist into early 2016.
The Bureau of Meteorology's latest ENSO wrap-up released this week reports tropical Pacific sea surface temperatures are more than 2°C above average, exceeding El Niño thresholds by well over 1°C, and at levels not seen since the 1997–98 event.
In the atmosphere, tropical cloudiness has shifted east, trade winds have been consistently weaker than normal, and the Southern Oscillation Index (SOI) is strongly negative.
Most international climate models surveyed by the Bureau of Meteorology indicate El Niño is likely to peak towards the end of 2015.
Typically, El Niño is strongest during the late austral spring or early summer, and weakens during late summer to autumn.
The Indian Ocean Dipole (IOD) is in a positive phase, having exceeded the +0.4°C threshold for the past eight weeks.
Recent values of the IOD index have been at levels not seen since the strong 2006 positive IOD event. Conversely, the Indian Ocean remains very warm on the broader scale.
Four out of five international models suggest the 2015 positive IOD event will persist until November, when it typically breaks down due to monsoon development.
El Niño is usually associated with below-average spring rainfall over eastern Australia, and increased spring and summer temperatures for southern and eastern Australia.
A positive IOD typically reinforces the drying pattern, particularly in the southeast.
However, sea surface temperatures across the whole Indian Ocean basin have been at record warm levels, and appear to be off-setting the influence of these two climate drivers in some areas.
