41% probability of below-normal monsoon, says IMD's second stage forecast

The India Meteorological Department has predicted normal rainfall during this southwest monsoon in its second stage long range forecast released today. “Rainfall over the country as a whole for the 2018 southwest monsoon season (June to September) is most likely to be NORMAL (96% to 104% of long period average (LPA)),” the press release said.

According to the forecast, north-west India will get the highest overall rainfall during the June-September period.  Overall rainfall in northeast India will be the lowest this monsoon seasons. July is likely to be the wettest month. However, the model error for both season rainfall and monthly rainfall are both high at ± 8 % and ± 9% respectively.

Quantitatively, the rainfall percentage has remained the same at 97% of the LPA (Long Period Average) with a model error of ±4%.

It is to be noted that during the first stage long-range forecast issued on April 16, IMD had predicted 44% probability of below-normal monsoon this year. The second stage forecast has predicted 41 per cent probability of below-normal monsoon (deficient – 13% | below normal – 28 %).

Indian Ocean Dipole and El Nino

The global climate models, according to IMD, indicate that conditions over the Pacific likely to continue to be neutral during most part of the monsoon season and weak El Nino conditions may develop after the monsoon season. El Niño is the unusual warming of surface waters in the eastern tropical Pacific Ocean, which weakens trade winds that blow from South America to Asia, leading to reduction and uneven distribution of rainfall in Indian sub-continent.

What could be of major concern is a weak negative Indian Ocean Dipole (IOD) conditions that are likely to develop during the middle of the monsoon season and continue to persist till the early part of the post-monsoon season. During weak IOD conditions, the eastern equatorial Indian Ocean becomes unusually warm while the western tropical part of the ocean near the African coast becomes relatively colder. This effect obstructs the progression of monsoon over India. Currently, warm neutral IOD conditions are prevailing over the Indian Ocean.