The Southwest monsoon is likely to be delayed this year, with the onset expected in Kerala on June 6 instead of June 1, the India Meteorological Department (IMD) said Wednesday in its monsoon onset forecast for 2019.
“Upon reaching the south Andaman Sea, the monsoon may take three to four days additionally to cover the Andaman Sea and further over to the Andaman and Nicobar islands. We expect the monsoon to arrive over Kerala only around June 6,” D S Pai, head of IMD’s Long Range Forecast (LRF), told The Indian Express.
The delay, meteorologists said, is due to the presence of a strong mid-latitude regime which is preventing the otherwise smooth entry of the monsoon currents from over the Bay of Bengal.
What the delay means
The time of onset has little bearing on the quality or amount of rainfall during the monsoon. But a late onset has the potential to delay the arrival of the monsoon to other parts of the country as well, particularly states across south India. However, it does not mean that the arrival of monsoon over the entire country will be delayed since its northern progression depends on local factors.
“The tropical regime or simply the monsoon currents are being oppressed by the prevailing mid-latitude regime, which is why these currents may take longer to establish over the mainland. Besides, the continuous flow of strong western disturbances, too, is making it difficult for the presently weak monsoon currents to penetrate,” said Pai who is also head, Climate Research and Services, IMD, Pune.
IMD officials said that the Southwest monsoon will likely arrive over the south Andaman Sea around May 18 or May 19.
The onset marks the beginning of the four-month, June-September monsoon season over India, which brings over 70 per cent of the country’s annual rainfall.
In its season’s first stage Long Range Forecast (LRF) issued last month, the IMD had predicted that the upcoming monsoon would be “near normal.” A rainfall up to 96 per cent of the Long Period Average (LPA) is likely to be received over the country from June to September this year, it said.
The Long Period Average (LPA) of the monsoon season over the country is 89 cm, calculated for the period 1951-2000.
If realised, this will be the first time since 2013 when the Southwest monsoon will make a delayed onset over the Indian mainland, in a departing trend from the last two years.
In 2017, the onset over Kerala occurred two days in advance (May 30) whereas in 2018, the onset was realised on May 29 – three days before the normal onset date over Kerala.
Since the winter of 2018, there have been strong and frequent flows of western disturbances, which is ongoing. This season, these westerlies are reported to be passing through more southern latitudes than its normal position, for this time of the year.
Even after the monsoon onset over Kerala, its progress, according to the IMD, will remain slow owing to these conditions. “The monsoon may take longer to reach and cover regions up to Central India,” said another senior Met official from Pune.
However, the progress of the monsoon to other states will also be governed by the local weather factors, formation of cyclonic circulations and troughs, that can enhance the chances of the monsoon’s progress.
“If there are conducive local weather conditions formed after the monsoon onset, the progress to other parts may even take the normal course. But, we can say more about it only after its arrival over Kerala is recorded,” said Pai.
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