Summer Monsoon of 2019:Understanding the Performance So Far and Speculating about the Rest of the Season

The summer monsoon of 2019 began with a massive deficit in the all-India June rainfall of about 33% of the mean. This led to considerable anxiety since a large deficit in June had occurred last in the summer monsoon of 2014, which had turned out to be a drought. Here, we have attempted to unravel the factors that led to the deficit in June 2019 and also the above-normal rainfall in July. We show that the deficit in June 2019, as that of June 2014, can be attributed to the El Niño. The phase of the other important mode, Equatorial Indian Ocean Oscillation (EQUINOO), has been favourable throughout and led to the recovery of the monsoon in July when the El Niño weakened. It is expected that EQUINOO will play an important role in determining the rainfall in August and September, and hence the seasonal rainfall in 2019. Analysis of cases like 2003 and 2008, when the positive phase of EQUINOO lasted only during June and July and of 2007, when it lasted throughout the season has given an insight into the role of the sea surface temperature (SST) of the western equatorial Indian Ocean (WEIO) in sustenance of the positive phase of EQUINOO. We find that, unlike in 2003 and 2008, the SST of the WEIO has started increasing in late July, partly due to the mechanism which operated in 2007 and has led to a positive SST anomaly by 10 August, whereas sustained cooling has led to a negative SST anomaly over eastern equatorial Indian Ocean. Since conditions now appear to be favourable for sustenance of a positive phase of EQUINOO, it is expected that the seasonal rainfall will be above normal.