"Below-normal rainfall is likely over broad areas of western, central and south-western parts of the region," Dr DS Pai, head of regional climate centre, India Meteorological Department (IMD), said when releasing the forecast of SASCOF-5 a group of global weather experts affiliated to the World Meteorological Organisation (WMO) in Pune on Wednesday.
Normal rainfall is likely over broad areas of northwestern and eastern parts and some island areas in the southern-most parts of the region.
The consensus outlook for the 2014 southwest monsoon rainfall over South Asia was developed through an expert assessment of prevailing global climatic conditions and forecasts from different climate models from around the world as well as inputs from eight South Asia countries Afghanistan, Bangladesh, Bhutan, Maldives, Myanmar, Nepal, India and Sri Lanka and experts from IMD, Indian Institute of Tropical Meteorology, the US, Japan and UK.
The map presented at the forum indicated there could be below normal rainfall in 80% of India. Dr Pai, however, refused to comment on any India related queries.The IMD forecast for India will be released in Delhi on April 24.
There was a strong consensus among experts at the forum about the possibility of an El Nino event during the summer monsoon. However, it is recognized that there is uncertainty in the intensity of the El Nino event. Experts also arrived at a consensus about the potential for adverse impacts of El Nino on monsoon rain over the region. Pai pointed out that other regional and global factors can also affect monsoon rainfall patterns over the region.
So far, there have been 14 El Nino events since 1951. Eight such events resulted in deficient monsoon, Pai explained. He was also quick to point out that there have been years where monsoon was normal despite the El Nino factor, as in the case of 1999.
In general, El Nino starts around March-April-May, warms slowly and reaches its peak around December. Next year, prior to the spring season, it weakens. Very rarely, it may continue further for two years.
El Nino can produce significant economic and atmospheric consequences worldwide and occurs every 3-7 years, lasting about a year. Recent major events occurred in 1982-1983 and 1997-1998, which was the strongest ever recorded so far.
According to experts at SASCOF, during February and through the early part of March, El Nino-Southern Oscillation (ENSO) conditions in the equatorial Pacific were on the borderline of weak La Nina and cool neutral. But a subsequent warming trend in sea surface temperatures over the region through mid-April caused ENSO conditions to become warm neutral. At the same time, sub-surface temperatures in tropical Pacific also warmed to levels generally observed prior to an El Nino event, the experts noted.
Latest forecasts from almost all ENSO prediction models indicate continuation of the warming trend, with sea surface temperatures over the equatorial Pacific remaining neutral during the northern hemisphere spring season and then developing into El Nino conditions during the southwest monsoon season with a probability of 60%.
Significantly, the WMO El Nino/La Nina update issued in mid-April also indicates a fairly large potential for an El Nino, most likely by the second quarter of 2014.
El Nino conditions during the monsoon season are known to weaken South Asian summer monsoon circulation and adversely impact rainfall over the region. However, their impact on regional distribution of rainfall varies from year to year.