After the 2015-16 El Nino reached its peak in early December, forecasters started to watch for the eventual dissipation of the El Nino and how the things will proceed thereafter.
While there were lots of uncertainties in the modeling during the climatologically spring season (March-May, where the forecast skill is low), the latest update from Columbia university shows for around 70% chance for La Nina during July-September period.
Last couple of weeks, the cold tongue in sub-surface anomalies has expanded and is pushing towards the surface across the equatorial Pacific Ocean. Thus, probabilities of La Nina conditions establishing around July is high.
When La Nina conditions persist for three-consecutive month from July-September, weather agencies NOAA BOM will officially declare the arrival of La Nina.
While El Nino is defined as above-average sea surface temperatures over central-eastern equatorial Pacific ocean, La Nina is characterized by cooler than normal ocean temperatures in the same region.
There are some questions on the upcoming La Nina event that if La Nina develops, how strong will it be? How long will it last?
Although it is difficult to predict months in advance, the history suggests that a Super El Nino event was followed by a multi-year cold event.
In the above data, we can arrive at a correlation that there seems to be significant relation with patterns responding strongly in opposite directions. While 1997, the previous Super El Nino flipped to strong La Nina, 1982 event had flipped to weak multi-year La Nina. There wasn’t much sub-surface cooler anomalies to have a strong La Nina event as seen below, and hence cannot be compared with 2016 which has wide expansion of cold tongue in sub-surface.
Another interesting year to note is the 1988 – which flipped to a Super La Nina following a double-peaked El Nino in 1986-87. The sub-surface cooler anomalies were impressive with below -4C departures during March and finally ended up as Super NINA.
So, will 2016 see such a similar La Nina event? If so, can it again last long? With 2015-16 El Nino being strongest in record books, chances of a multi-year cold event with first year NINA being moderate and the following year La Nina event ending up stronger is high.
LA NINA INFLUENCE IN ASIA
With El Nino playing a huge role in leading to deficit monsoon across India in 2015-16, prospects for above-normal monsoon looks good with La Nina developing in the Pacific Ocean. With West Pacific typhoon season getting suppressed, South-West Monsoon will perform better compared to last two years.
Much of the country is likely to get above-normal rainfall during June-September period with exception being the North-East portion of India that may end below normal.
At the same time during the post monsoon season (October-December), La Nina generally tends to enhance the tropical activity in Bay of Bengal. The cooling of equatorial east-central Pacific waters will tend to enhance the warmth across E Indian ocean and in the Mari-time Continent.
With Indian ocean Dipole likely to remain in negative state during this time period, we could see above-normal tropical activity in Bay of Bengal.