Home Science El Niño Watch...

El Niño Watch continues, signs of a positive Indian Ocean Dipole emerge

Enso

MELBOURNE, Australia — The El Niño – Southern Oscillation (ENSO) remains neutral. While climate models suggest some easing in the chance of El Niño in 2018, half of the surveyed models still indicate an event is possible, reports the Australian Government Bureau of Meteorology.

When assessed with current observations, the Bureau’s ENSO Outlook therefore remains at  Watch, meaning the chance of El Niño in 2018 remains around 50%; double the normal likelihood.

Oceanic and atmospheric indicators of ENSO are generally neutral. While sub-surface waters have recently warmed, sea surface temperatures in the tropical Pacific Ocean are only slightly above average.

Likewise, the Southern Oscillation Index remains weakly negative, and short of El Niño levels. Trade winds have recently been weaker than usual in the western Pacific, and may remain weak in the coming weeks. Weakened trade winds can be a precursor.

Climate models now indicate less warming of the tropical Pacific is likely compared with last month. As a result, fewer models now predict an El Niño in 2018—only three of eight models exceed thresholds in 2018, and a fourth does so in early 2019. The rest remain neutral.

The Indian Ocean Dipole (IOD) index has exceeded the positive IOD threshold (+0.4 °C) in the last fortnight.

However, it would take several more weeks of similar values before a positive IOD event is considered established. Model outlooks currently suggest positive IOD values are likely to continue through the austral spring, before returning to neutral values in late November to December.

A positive IOD and El Niño during spring typically means below average rainfall for southern, eastern and central Australia. When a positive IOD and El Niño occur together, the reduction in rainfall is often more widespread.