With all indications suggesting India heading for another year of normal rainfall, the Met department evinces its readiness to make its first forecast for this season’s monsoon rainfall, to be expected on Monday. According to the weather scientists, prevailing conditions are favourable for a good rainfall in the June-September monsoon season.
In the opinion of scientists, India receives 89 cm of rainfall during the four-month monsoon season, which is almost 75 percent of its annual rainfall. Last year, the country received rainfall that was 95 percent of its long-period average.
The most agreeable condition right now appears to be the “near-neutral” to “neutral” ENSO (El Nino Southern Oscillation) in the equatorial Pacific Ocean, off the coast of South America. Neutral is said to be neither El Nino nor La Nina.
ENSO refers to anomalies (deviations from usual sea-surface temperatures in the Pacific Ocean) in the sea-surface temperatures in the Pacific Ocean which have sometimes been observed to have a near-decisive impact on the monsoon rainfall. A warmer than usual sea-surface temperature, referred to as El Nino condition is associated with a suppressed monsoon rainfall in India, while the opposite, called La Nina, is known to help the rainfall.
Global climate models are exhibiting near-neutral conditions prevailing in the Pacific Ocean right now and are predicting that it will remain this way through most of the year.
“La Nina conditions are present. Equatorial sea surface temperatures (SSTs) are below average across the central and eastern Pacific Ocean. A transition from La Nina to ENSO-neutral is most likely (~55% chance) during the March-May season, with neutral conditions likely to continue into the second half of the year”, says the latest bulletin from the Climate Prediction Centre of the National Oceanic and Atmospheric Administration (NOAA) of the United States.
Australia’s Bureau of Meteorology has been reporting for at least two weeks now that the ENSO had already turned neutral.
“The El Niño-Southern Oscillation (ENSO) remains neutral. Most models predict a neutral ENSO pattern will persist through the southern autumn and winter”, it said in its latest report.
“Most atmospheric and oceanic indicators of ENSO are at neutral levels. Sea surface temperatures in the central Pacific are close to average for this time of year. Beneath the surface, the tropical Pacific Ocean is slightly warmer than average, but well within the neutral range,” it also said.
While a La Nina condition would have been more suitable for the monsoon, scientists say normal rainfall can be expected even in neutral ENSO condition.
“When the anomalies are too small or absent, the monsoon rainfall over India is normal. The forecast now is that the SST anomalies in the eastern tropical Pacific are ENSO-neutral during the coming summer and hence we can expect a normal monsoon this year,” said Bala Govindasamy of the Centre for Atmospheric and Oceanic Sciences at the Indian Institute of Science.