Neutral El Nino conditions prevail currently in the equatorial Pacific Ocean, but the Indian Met Department (IMD) has assessed that weak El Nino conditions may develop in the coming months, and ‘continue for a short period’.

The IMD has said this based on the latest update from its Monsoon Mission Climate Forecast System, but doesn’t elaborate on implications for year the 2019 South-West monsoon, which is four months away.

Prime influencer

El Nino (warming of the Central/Eastern equatorial Pacific Ocean) and alter-ego La Nina (cooling of the same ocean waters) are considered to be one of the prime influencers of the Indian monsoon, though without proven one-to-one connection.

Equatorial Pacific warm water volume, assessed in February-March. is one of the five predictors the IMD uses to assess the likely monsoon pattern for the country. The first forecast statement in the series will come out in April.

El Nino generally suppresses monsoon rainfall; La Nina generally increases it. But, this relationship between El Nino and poor Indian monsoon does not necessarily hold up every time.

El Nino years tend to be drier than average, but one of the strongest El Nino years of the century (1997-98) produced a monsoon season with above-average rainfall.

Complicated link

During a La Nina year, rains have been above or around average. But at least a dozen leading droughts since 1950 have coincided with El Nino. Still, El Nino doesn’t always mean drought.

It is in this context that various models have started making assessment of the evolving situation in the Pacific.

The Australian Bureau of Meteorology has made a forecast that aligns more or less with the IMD’s prediction.

But it has qualified the statement, by saying that predictions made in late January-February tend to have lower accuracy than those made at other times of the year.

So current forecasts beyond May should be used with some caution.

The Bureau’s outlook is at El Nino ‘Watch’ (after being downgraded from an El Nino ‘Alert’), meaning there is approximately a 50-per cent chance of El Nino developing during March-April-May. This is twice the normal likelihood.

Model speak

Five of eight climate models indicate the Central Pacific is likely to reach borderline or weak El Nino levels during September-November, with four models remaining above these threshold levels into December-February.

According to the Application Laboratory of Jamstec, the Japanese national forecaster, warmer-than-normal sea surface temperatures have been observed during this winter across the whole tropical Pacific.

The current state will continue through March to May. The tropical Pacific will return to a normal state during the following summer (coinciding with the Indian monsoon).

The US National Oceanic and Atmospheric Administration (NOAA) said the pattern of anomalous convection and winds are consistent with El Nino.

There is 55 per cent chance that weak El Nino conditions may continue from March to May.