Monsoon withdrawal to be begin next week

September deluge ensures close to normal rainfall across country

The monsoon is likely to begin withdrawing from the mainland from October 6, said the India Meteorological Department as the country recorded an average of nearly 87 cm of rainfall across subdivisions, just short of the nearly 88 cm it normally receives during the monsoon. The quantum of rains during the monsoon is counted as that received between June1- September 30.

September rainfall, at 223 millimetres (mm) has been the second highest since 1993 when it got 239 mm (40% above normal). In 2019, India recorded nearly 250 mm, or about 52% more than normal.

Had it not been for the extraordinary rainfall last month, India could very well have ended up with deficit rainfall. With a weakening of the rainfall that began in mid-July and lasted most of August, the rainfall deficit in India had widened to nearly 24%. As of Thursday India has received 99% of its monsoon rainfall.

At the start of the monsoon, the IMD had forecast rainfall in the four months to be “above normal” or around 101% of the Long Period Average (88 cm). After a staggering deficit in August, the second rainiest month, it revised it to saying that this would be “at the lower end of normal” without specifying a fresh number.

As predicted

However, the IMD did also say that September rainfall would be above normal, or “greater than 110%” of the normal for the month. September rainfall was expected to be good on the back of transitioning temperatures in the Central Pacific Ocean where a La Nina — characterised by colder than normal sea surface temperatures — was taking shape.

While September is usually the month that marks the beginning of the end of the monsoon’s four-month sojourn over India, both 2020 and 2019 have seen rain spikes during the month.

In 2019, September rain was a staggering 152% or close to 25 cm, close to what the country gets in August (26 cm), considered the second rainiest of the monsoon months. That year also saw India get the highest monsoon rainfall since 1994. Last September’s rainfall at 17.7 cm was not too high but more than normal.

D.S, Pai, Head, Climate Research Services, IMD, Pune said while three Septembers of excess monsoon rains was unusual, it wasn’t yet indicative of a trend.

“There is always variability within the monsoon and the rainfall that we saw in September was part of it. We’ll have to wait for longer to see if there’s any trend,” Mr. Pai said.

Across the regions, central India saw 83% more rain than normal, northwest India 40% and southern India 24% above normal. However, northeastern and eastern India saw a 30% reduction. M. Mahapatra, Director General, IMD, said typically, heavy rains in central India correspond to weaker rains in the northeast because of the movement of the monsoon system.

Other factors that contributed to strong September rains were favourable conditions in the Indian Ocean as well as a rain-bearing system in the Bay of Bengal that resulted in Cyclone Gulab that passed through Andhra Pradesh but whose effects were felt as far as Maharashtra, bringing in torrential rain in the State.

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