Night follows day, summer follows spring: but does La Nina always follow El Nino?
During the past month, the abnormally warm waters along the eastern equatorial Pacific that typify an El Nino event, have disappeared. In fact, the more normal condition of the colder sub-surface waters welling up to the surface has returned.
It is this up-welling that creates the good fishing grounds off the Chilean coast and it is the disappearance of fish that has historically been the first indicator of a developing El Nino.
El Nino is one extreme end of what is known as the Southern Oscillation. Warm surface water sloshes in slow motion from the western Pacific to the eastern Pacific during the El Nino phase, then it sloshes back again in slow motion to create La Nina.
The development of either of these phenomena is slow and irregular which means that there are long, “normal”, periods.
But, after a major El Nino, such as the 2015-16 one, it is not surprising to see a swing through neutral to La Nina. Historically, La Nina has followed several strong El Nino events, including the 1997-98 event, possibly the strongest one on record.
Most computer models have predicted the end of El Nino and a brief period of neutral EL Nino-Southern Oscillation conditions by the end of May. From then on, there is increasing uncertainty as to the timing and strength of any La Nina phenomenon.
Overall, La Nina is favoured to develop during the northern hemisphere summer of 2016, with about a 75 percent chance of La Nina during the autumn and winter of 2016-17.
La Nina can be as disruptive to the world’s weather as its opposite number. The known effects are sometimes opposite, for example, rainfall is enhanced over Indonesia, Malaysia and northern Australia. Wetter than normal conditions are also observed over southeastern Africa and northern Brazil during the northern winter season.
During the northern summer season, the Indian monsoon rainfall tends to be greater than normal, especially in northwest India.
More rain during the Indian Monsoon season and more rain over Indonesia, Malaysia and the Philippines, let alone northern Australia could be seen as good news.
Given the shortage of recent rains and heatwaves enhancing evaporation, drought has become common and a good dose of wet weather would go some way to reducing it.