Incessant rains in September have already given an impression that this monsoon spell may not end soon. As the monsoon extends beyond what is considered 'normal', experts say that the withdrawal may delay further.
Delay continues
The normal date for the beginning of withdrawal in west Rajasthan is September 1, which has not started yet. Over the past decade, the monsoon withdrawal has never really kept up with this date; four times out of the last eight monsoon seasons, the retreat started after September 20. In 2018, the withdrawal began on September 28, and this year might also be the same.
"There has hardly been any rainfall in most of Western Rajasthan since the last seven days. The jet-stream reversal—an important parameter indicating the end of the southwest monsoon—has started. Thus, we can expect the monsoon's withdrawal to commence from extreme western Rajasthan by September 27", says Akshay Deoras, a meteorologist and researcher at the University of Reading, UK.
The changeover of lower-level circulation from 'cyclonic' to 'anti-cyclonic' indicates the withdrawal. The India Meteorological Department (IMD) declares official withdrawal date for a region after three major criteria have been met: no rains for continuous five days, the establishment of the lower-level anticyclone, and considerable drop in moisture content evident in satellite images.
Withdrawal in central India
Elena Surovyatkina, a leading weather expert, feels that the withdrawal may delay up to the third week of October in central India. A scientist at the Potsdam Institute for Climate Impact Research (PIK), Germany, Elena told Business Line that the withdrawal might happen in central India between October 14 and 24.
However, Akshay says that the withdrawal from most of central India can be expected in the first fortnight of October. The normal date for withdrawal in central India is October 1. Central India has witnessed one of the wettest monsoon seasons in recent history with 23% excess rainfall till now.
The new normal
Formation of persistent low-pressure areas in late September is said to be the primary reason behind the delay in the withdrawal of monsoon. Very high temperatures in northwest India, as well as in Pakistan and Afghanistan, have also contributed to the delay.
Reports suggest that owing to unprecedented changes in monsoon over the past decade, IMD is considering the revision of its 'normal' onset and withdrawal dates. The present normal date of monsoon withdrawal, September 1, was set in 1941 and has not been revised in the past 78 years.
Unlike the monsoon's onset, its withdrawal witnesses considerable deviations from the normal dates and hence declaring the withdrawal is much harder than declaring the onset. To avoid situations when the rainfall occurs after the declaration of withdrawal, the agencies try to be cautious with the announcement. However, as the withdrawal is a rapid process, it happens from nearly on time for most of the country despite the substantial delay in the beginning.
"Having said that, there's certainly a need to revisit these dates in the case of Northwest India since the total duration of the southwest monsoon in this part of the country is less than other states," concludes Akshay.
