The Australian Bureau of Meteorology has upgraded the outlook for a warming trend in the Equatorial Pacific from an El Nino 'watch' to El Nino 'alert', indicating a raised probability of an El Nino this year.

This means the chance of El Nino developing in 2019 has increased to approximately 70 per cent, around triple the normal likelihood, the Bureau said in its latest updated on Tuesday.

Impact on monsoon

An El Nino has been known to be associated with less rainfall or dry conditions for India during the South-West monsoon season (June-September), though without conclusive cause-effect relationship.

It is the abnormal warming of the Equatorial East relative to the West that triggers an El Nino, and exactly the opposite during a La Nina. The Indian monsoon is known mostly to benefit from a La Nina.

But the country could likely draw some comfort from the fact that forecast agencies also see an evolving positive phase of the Indian Ocean Dipole (IOD), which mimics the El Nino-La Nina phenomenon in its own backyard.

During a positive phase of the IOD, the western basin of the Indian Ocean warms up relative to the east, boosting the monsoon flows. Exactly the opposite happens during a negative IOD phase.

According to the Australian Bureau, current outlooks suggest the IOD is likely to remain neutral for the remainder of the spring-summer, but suggest a positive IOD may form later in June-July-August.

This also coincides with the first three and most rainy months of the Indian monsoon. A positive IOD typically means a wetter monsoon, irrespective of concurrent conditions in the Pacific.

Positive IOD outlook

The Application Laboratory of the Japanese national forecaster Jamstec too has predicted the evolution of a positive IOD phase from late summer. But there is currently a large uncertainty with respect to its amplitude.

Meanwhile, the United States (US) National Oceanic and Atmospheric Administration (NOAA) has a different take on the Pacific conditions. Since early June 2018, near-to-above warming tend was noticed across most of the Pacific, it said.

During February 2019, the positive sea-surface temperature anomalies strengthened across most of

the Equatorial Pacific, the NOAA said in its latest update.

But since early March, these anomalies have weakened slightly across most of the Pacific, it said, and added that 'El Nino conditions are present' as of now.

The pattern of anomalous convection and winds are consistent with an El Nino. The NOAA assessed that weak El Nino conditions are likely during the spring (80 per cent possibility) and into the summer (60 per cent).

The last El Nino, a strong one, lasted from 2014 to 2016 and had adversely impacted the Indian monsoon with deficits of 12 per cent in 2014 and 14 per cent in 2015, before improving to three per cent in 2016.