Weather scientists have predicted normal monsoon in June-September 2018 monsoon season as prevailing conditions as well as neutral ENSO were favourable for good monsoon rainfall. India receives 89 cm of rainfall during four-month monsoon season, which is almost 75% of its annual rainfall. In 2017 monsoon season, country as whole had received rainfall that was 95% of its long-period average.
The most important favourable condition for good monsoon is near-neutral to neutral ENSO (El Nino Southern Oscillation) in equatorial Pacific Ocean, off coast of South America. Global climate models are showing near-neutral conditions prevailing in Pacific Ocean and it will remain this way through most of the year.
Moreover, La Niña conditions are present and equatorial sea surface temperatures (SSTs) are below average across central and eastern Pacific Ocean. The transition from La Niña to ENSO-neutral is most likely during March-May season, with neutral conditions likely to continue into second half of year. SST anomalies in eastern tropical pacific are ENSO-neutral during coming summer and hence normal monsoon is expected this year.
ENSO (El Nino Southern Oscillation)
ENSO refers to anomalies in SSTs in Pacific Ocean off coast of South America which has sometimes been observed to have near-decisive impact on monsoon rainfall. In El Nino, a warmer than usual SST is observed in Pacific Ocean off coast of South America . This condition is associated with suppressed monsoon rainfall in India. La Nina is opposite ENSO and is more favourable for monsoon. It is known to help monsoon rainfall in India. When anomalies (deviations from usual SST in the Pacific Ocean) are too small or absent, monsoon rainfall over India is normal.