Monsoon likely to withdraw late this year, Met predicts; more rain in store
The monsoon has entered an active phase from Saturday because of a low-pressure system that will travel across central and northwest India, bringing the region widespread and heavy rain over the next four to five days, the India Meteorological Department (IMD) warned on Saturday.
The monsoon starts waning in September and usually begins withdrawing from September 17.
But the Met department’s extended range forecast indicates that there is likely to be widespread rain over the country, including northwest India, till around September 30.
Normally, around six depressions form through the course of the monsoon season, but this time the first monsoon depression is likely to form only in the next 24 to 48 hours.
“Normally, however, July and August are the main monsoon months, when active spells are common. We have also indicated that monsoon deficiency will reduce and settle in the normal category by the end of the season,” said OP Sreejith, head, climate monitoring and prediction group, IMD.
“The formation of fewer low-pressure systems compared to the climatology and absence of their longer westward movements during August contributed to the large deficient rainfall in central India as well as all India,” the IMD said in a statement on Friday.
So far, the monsoon deficiency is 7% across the country.
August received 24% less rainfall than it usually does, but September has so far seen 16.4% excess rain, showed data from the Met department.
A Negative Indian Ocean Dipole over the tropical Indian Ocean — a phenomenon where the western Indian ocean becomes colder than the eastern one and which is unfavourable for monsoon — prevailed throughout August, contributing to deficient rainfall.
There were also fewer typhoons in the West Pacific and so there was an absence of westward movement of their remnants into Bay of Bengal. This led to fewer low-pressure systems forming over Bay of Bengal.
“But now West Pacific is very active. The sea surface temperatures over central and eastern equatorial Pacific Ocean are also cooler indicating weak La Nina setting in. This is also associated with good rains,” added Sreejith.
La Niña refers to the large-scale cooling of the ocean surface temperatures in the central and eastern equatorial Pacific Ocean, coupled with changes in the tropical atmospheric circulation, namely winds, pressure and rainfall. It usually has the opposite impacts on weather and climate as El Niño, which is the warm phase of the so-called El Niño Southern Oscillation (ENSO).
ENSO has a major influence on weather and climate patterns such as heavy rains, floods and drought. In India for example, El Nino is associated with drought or weak monsoon while La Nina is associated with strong monsoon and above average rains and colder winters.
“Monsoon will be in its active phase for the next 4-5 days. This is mainly because a low-pressure area is lying over east central and adjoining northeast Bay of Bengal which will intensify and move west-northwest wards and monsoon trough will be active. The combination of these two will bring widespread rains to central India starting from Odisha covering Maharashtra, Madhya Pradesh, Jharkhand, Delhi, and some more parts of northwest India during the next few days,” said M Mohapatra, director general, IMD.
Heavy rains in September can impact standing crops, particularly pulses, experts said.
“Pulses are particularly vulnerable to damage. However, the heavy rain spell will fill reservoirs in Gujarat, Rajasthan where there was a very long dry spell in August which will be useful for the Rabi crop,” said Mahesh Palawat, vice president, climate change and meteorology, Skymet Weather.