The beginning of the journey towards Southwest Monsoon 2020 is not very far away. Very soon the countdown to the four-month long season would begin. Predicting Monsoon has always been challenging for forecasters worldwide. Monsoon rains continue to be of surprising nature, with the season taking any turn during its course. It has a track record of turning fairground into the topsy- turvy ride and vice versa. The most recent example would be of Southwest Monsoon 2019 which was initially predicted to be mild but finished with a deluge not just for the year but in the last 25 years.
While forecasting the Monsoon season, there are three oceanic parameters taken in to account: El-Nino, IOD and MJO. The Indian Ocean Dipole (IOD), sometimes called " Indian Nino" pertains to the temperature variation in the west and east equatorial Indian Ocean. It also has a history of rescuing Indian Monsoon when under adverse El-Nino conditions. And therefore it is also called a 'saviour' of monsoon. It had been a game-changer last year wherein it rewrote the monsoon chapter defying predictions made worldwide. We had witnessed the longest as well as the strongest spell of IOD, which persisted for an extended period from May to December 2019. All through this while, IOD values were above the threshold mark of 0.4 and finally peaking to the maximum of 2.2 degree centigrade, that is highest since 1997.
As per historical records, the occurrence of consecutive episodes of positive IOD as well as negative IOD are not very common. Statistically, IOD has a ratio of 1:1:4 which is positive, negative and neutral respectively. Because of the shift of Inter Tropical Convergence Zone (ITCZ) in the southern hemisphere during Indian winters and Spring, IOD is unable to show up. While we are transiting to the Pre Monsoon season and so can expect the IOD now to come up with reliable predictions to fall upon.
As per the preliminary forecast by the Bureau of Meteorology Australia, this ocean index is going to stay neutral. The respective values are likely to be 0.1 in June, -0.2 in July and -0.2 in August 2020.
The majority of weather models are predicting neutral duo of El- Nino, and IOD this season. It means that monsoon is going to ride on its own dynamics. We understand that Monsoon is a global and ocean driven phenomenon but may not get influenced much by the oceanic parameters. To us, it appears that the ITCZ, Tibetan Plateau heat and Madagascar High are going to play a dominant role.