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Sunday, July 15, 2018

Conditions for normal monsoon, Met forecast soon

Weather scientists said prevailing conditions were favourable for a good rainfall in the June-September monsoon season. Last year, the country as a whole received rainfall that was 95 per cent of its long-period average.

Written by Amitabh Sinha | Pune | Published: April 14, 2018 6:15:26 am
 met department, weather forecast, monsoon rainfall, monsoon 2018, el nino, indian express, el nina India receives 89 cm of rainfall during the four-month monsoon season, which is almost 75 per cent of its annual rainfall. (Representational Image)

AS THE Met department gets ready to make its first forecast for this season’s monsoon rainfall, expected on Monday, all indications are that the country was headed for another year of normal rainfall. Weather scientists said prevailing conditions were favourable for a good rainfall in the June-September monsoon season. Last year, the country as a whole received rainfall that was 95 per cent of its long-period average. India receives 89 cm of rainfall during the four-month monsoon season, which is almost 75 per cent of its annual rainfall.

The most important favourable condition right now happens to be the “near-neutral” to “neutral” ENSO (El Nino Southern Oscillation) in the equatorial Pacific Ocean, off the coast of South America. ENSO refers to anomalies in the sea-surface temperatures in the Pacific Ocean which has 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 showing 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 Niña conditions are present. Equatorial sea surface temperatures (SSTs) are below average across the central and eastern Pacific Ocean. A transition from La Niña 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 — neither El Niño nor La Niña. 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 said.

A La Nina condition would have been more favourable for the monsoon but scientists say normal rainfall can be expected even in neutral ENSO condition. “When the anomalies (deviations from usual sea-surface temperatures in the Pacific Ocean) 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.

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