NEW DELHI: La Nina conditions in the Pacific Ocean that generally favour good monsoon rains in India have ended, the US govt agencies declared late Thursday, with the world’s largest ocean likely to stay in ‘neutral’ phase till winter. This could be good news for India’s monsoon, as it reduces the probability of drought or excess rainfall in the season, but it’s also likely to make monsoon forecasts trickier, experts said.
Adding to the difficulty of forecasters, conditions in the Indian Ocean too are likely to be ‘neutral’ till at least Aug, as per the latest Australian weather bureau update. Along with the Pacific, surface temperatures in the Indian Ocean play a major role in India’s monsoon, with the ocean’s ‘positive’ phase — when waters in western Indian Ocean are warmer than those in the east — generally boosting rains.
For the Pacific, the US’s Climate Prediction Center said in a release that there was more than a 50% chance that neutral conditions will stay till Sept. Its probability of persisting till the year-end was also higher than those of La Nina or El Nino, it said.
If this forecast holds true, this would be the first time in 12 years that the monsoon peri od, or the months immediately preceding or following it, won’t have presence of either El Nino or La Nina. These two opposite Pacific Ocean conditions are seen as most important among large scale weather features that determine how much rain India gets during the June-Sept period.
“When Pacific Ocean conditions are neutral, all scenarios are open for the Indian monsoon. However, the chances of a drought or a flood year are small. Generally, under neutral Pacific conditions, we don’t expect unwanted monsoon outcomes,” said M Rajee van, veteran meteorologist and former secretary of the Union earth sciences ministry.
During neutral conditions in the Pacific, also known as ENSO neutral phase, surface water temperatures in the ocean’s eastern and central equatorial regions are neither abnormally warm (El Nino conditions, which weaken Indian monsoon) nor too cool (La Nina). While this is said to be the ocean’s natural state, neutral years aren’t that common.
“Monsoon is more difficult to predict under such conditions. Forecasters have to be more careful and look closely into factors such as the state of the Atlantic Ocean. Internal dynamics can also play a role,” said Rajeevan, who is also IMD’s former monsoon forecaster.
As per the first monsoon forecast this year, made by private agency Skymet, total monsoon rainfall in India is likely to be 103% of the long period average, at the higher end of the normal range.
