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The southwest monsoon (SWM) rains over Kerala that usually commence by June 1 might get delayed by five days, according to the latest forecast by the India Meteorological Department (IMD) on May 15, 2019.
The forecast comes with a statistical error of (+/-) four days which means that the actual onset of SWM could be up to four days early or late. This means the onset could be any time between June 2 and June 10.
In the last 14 years, the IMD has got this prediction wrong only once in 2015 by six days, according to an IMD press release. In 2014 and 2016 it was off only by a day and in the last two years it was spot on. If it gets it right three times in a row remains to be seen.
Private weather agency Skymet Weather has also predicted a delay in the onset of SWM. It says Kerala will get its first monsoon rain by June 4 with an error margin of (+/-) two days. This means that the onset can be any time between June 2 and June 6.
Reasons behind this delay
Experts say before the monsoon’s arrival, certain features of its growth show up on the Indian mainland 15 days before. But they can’t be seen yet.
“When the SWM is about to arrive there should be certain changes in wind circulation, convective and temperature patterns over the Indian region which have not yet arrived,” DS Pai, an expert on monsoons at IMD, Pune told Down to Earth.
One major reason for this delay is the continued presence of a large swathe of winds known as the mid-latitude westerlies over the Indian sub-continent, a small part of which are the western disturbances (WDs).
Between May 11 and May 15, two active WDs affected the Western Himalayan region and the plains of North West India. This year has seen a continued presence of WDs after an apparent lull in December, which had lead to an extended winter season and is causing the delay in SWM season.
“Usually by this time these westerlies leave the Indian region and push more northwards but that has not happened,” said Pai. The SWM winds now have to cut through the prevailing winds which will take longer than usual, hence the delay.
Another reason could be the ongoing weak El Nino conditions in the equatorial Pacific Ocean. El Nino is the unusual warming of the equatorial Pacific Ocean and disrupts global wind patterns affecting climatic conditions in tropical areas like Africa, sub-tropical areas like India as well as the extra-tropical areas like North America. It has a strong correlation with the southwest monsoon season in India but no direct cause and effect.
According to Pai, El Nino could have had a role to play in this delay. But since several times SWM has arrived early even during El Nino years, nothing can be said for sure.
Will delay impact monsoon’s distribution and strength?
“This delay will have no effect on the strength of the rains or their distribution. Both these aspects are unrelated,” said Pai. On the other hand, Skymet has predicted a sluggish start to the SWM season.
Skymet says the El Nino impact will be seen in the first half of monsoon. “We expect the June rain to be 23 per cent less than long-period average (LPA). First half of July will also be less than normal,” said Mahesh Palawat, chief meteorologist at Skymet Weather.
“El Nino will start weakening by August and rainfall will improve from August till September. Our forecast for August is 102.5 per cent of LPA and for September it is 99 per cent,” he added.
The private weather agency also said there is a 70 per cent probability of a below normal SWM season. Overall India will receive 93 per cent of its LPA. The central, east and north eastern and southern parts of the country will receive 91 per cent, 92 per cent and 95 per cent of LPA of rainfall, according to Skymet’s forecast.
This is not good news for farmers suffering from drought sue to deficient rains last year.