An end to the El Niño Pacific Ocean warming event is within sight, according to the Australian Bureau of Meteorology (BoM). Tropical Pacific Ocean conditions have weakened to borderline El Niño-neutral levels.
Sea surface temperatures across the tropical Pacific Ocean have cooled further in the past fortnight, driven by cooler than average waters below the surface. Atmospheric indicators are also trending towards normal, says BoM in its latest report on the El Niño – Southern Oscillation (ENSO) phenomenon.
Trade winds have been consistently near normal for some weeks. Typical El Niño cloud patterns are dissipating and the Southern Oscillation Index (SOI), a measure of air pressure difference between Tahiti and Darwin, Australia, and a key indicator of Pacific Ocean conditions, while still negative, is steadily rising.
The Pacific Ocean appears to be heading from its warm El Niño phase to a calling La Niña phase with BoM estimating the likelihood of La Niña forming later in 2016 is around 50 per cent.
Climate models suggest the tropical Pacific Ocean will continue to cool, with seven of eight models surveyed by BoM exceeding La Niña thresholds by September 2016. However, individual model outlooks show a large spread between neutral and La Niña scenarios.
Very warm sea surface temperatures continue across large parts of the Indian Ocean. Likewise, ocean temperatures around Australia remain well above average. Warmth in these two regions may provide extra moisture for rain systems as they cross Australia during the coming months.
La Niña impacts
Globally, according to NASA, La Niña is characterized by wetter than normal conditions west of the equatorial central Pacific over northern Australia and Indonesia during the northern hemisphere winter, and over the Philippines during the northern hemisphere summer. Wetter than normal conditions are also observed over southeastern Africa and northern Brazil, during the northern hemisphere winter season. During the northern hemisphere summer season, the Indian monsoon rainfall tends to be greater than normal, especially in northwest India. Drier than normal conditions are observed along the west coast of tropical South America, and at subtropical latitudes of North America (Gulf Coast) and South America (southern Brazil to central Argentina) during their respective winter seasons.
|Index||to 17/4/2016||to 24/4/2016||to 1/5/2016||to 8/5/2016|
|NINO3||+1.0 °C||+0.6 °C||+0.5 °C||+0.5 °C|
|NINO3.4||+1.1 °C||+1.1 °C||+0.8 °C||+0.8 °C|
|NINO4||+0.7 °C||+0.9 °C||+0.9 °C||+0.8 °C|
Table shows weekly sea surface temperature anomalies over the four weeks to 8 May 2016 in various sectors of the Pacific – anomalies are relative to the 1961-1990 baseline.
Australian Bureau of Meteorology (BoM) ENSO Wrap-Up report for 10 May 2016.
NASA La Niña factsheet.