El Nino conditions in the Equatorial Pacific continue to be neutral into mid-December, an update by the Australian Bureau of Meteorology has said.
The El Nino-Southern Oscillation (ENSO) remains neutral, the Bureau said on Tuesday. Despite ocean temperatures being at El Nino levels, atmospheric conditions have failed to respond in kind.
The Bureau's overall outlook, however, remains at El Nino alert.
El Nino-Southern Oscillation refers to the interaction between the tropical Pacific Ocean (El Nino) and its overlying atmosphere (Southern Oscillation), which together produce a typical global influence on weather and climate.
An evolving El Nino in December and progressing in tandem with the northern hemisphere summer has coincided with a poor monsoon or drought for India in the subsequent June-September season.
While tropical Pacific sea surface temperatures (SSTs) are currently at El Nino levels, atmospheric indicators - such as cloudiness, pressure patterns, the Southern Oscillation Index (SOI) and trade winds - have generally remained neutral, the Bureau said.
This means the ocean and atmosphere are not reinforcing each other, or coupled. It is this coupling that defines and sustains an ENSO event, and results in widespread shifts in global weather and climate.
According to the Bureau, the natural seasonal cycle of tropical Pacific conditions means the likelihood of an ENSO event developing during mid-summer (December-January-February in Australia) is lower than at other times of the year.
FORECASTING SKILLS
This is because the difference in SSTs across the Pacific basin eases towards a minimum in late summer to autumn. Late developing El Nino events do occur, such as in 2006–07 and 2009–10, although there is no record of one starting in January.
Most models indicate SSTs in the tropical Pacific Ocean are likely to remain near or above El Nino levels until at least the middle of 2019. However, models typically have less skill when forecasting through the Australian (March-April-May).
If SSTs did maintain their current anomalous warmth through the Australian summer, it would increase the chance of El Nino emerging in 2019, the Bureau said.
Earlier, the UN Economic and Social Commission for Asia Pacific (UN ESCAP) and the Regional Integrated Multi-Hazard Early Warning System for Africa and Asia (RIMES) had come out with a similar outlook.
The Bangkok-based agencies had said that the evolving El Nino may weaken beyond February 2019, but caution should ideally be the watchword for vulnerable economies in the Asia-Pacific.