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Expert sees early onset of monsoon this year: IMD outlook awaited

Vinson Kurian Thiruvananthapuram | Updated on January 27, 2018 Published on April 13, 2017

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monsooon

May hit Kerala coast by May 26

Even as India Met Department (IMD) looks like not having readied its initial long-range monsoon forecast yet, a renowned researcher has opined that the rains might arrive early this year.

The monsoon may make an onset over the Kerala coast by May 25, says PV Joseph, who is not only an acclaimed researcher but also a former director of the IMD.

Longe-range outlook

The IMD normally releases its first long-range monsoon forecast (LRF) within the first fortnight of April. Last year, the first LRF was out on April 12.

On Thursday, it said that a building low-pressure area in the Bay of Bengal might go on to become a depression by Saturday. Global forecasts say it could grow into a cyclone, headed towards Myanmar/Bangladesh.

Meanwhile, private forecaster Skymet and other models have opined that the likely El Nino conditions in the Pacific could impact the monsoon, despite no one-to-one correlation between the two. The IMD’s take on this is eagerly awaited.

A majority of the ocean-atmosphere coupled models have predicted that El Nino conditions are likely to set in during the second half of the monsoon, Joseph told BusinessLine.

‘Pre-monsoon peak’

“We had a negative Indian Ocean Dipole during September to November last year. Such a condition is generally followed by an El Nino in the next year.”

“With an El Nino around,we may expect less than normal all-India rainfall this year,” he added.

An early monsoon onset cannot be taken to mean that it would perform well during the four-month-long season that extends from June 1 to September 30.

Joseph, who is often consulted by the IMD, based his assessment of the onset prospect on the observed ‘pre-monsoon rain peak’ phenomenon, represented by a band of raining cloud extending from Kerala eastwards into the Bay of Bengal.

His pioneering work on the phenomenon is among the key parameters considered by the Met Department for its forecasts.

Cyclonic storm

The 'pre-monsoon rain peak' can form any time between the first week of April and the second week of May. Its timing gives prior indication of the date of monsoon onset over Kerala.

For a normal monsoon onset that occurs on June 1, the raining band of cloud in the Bay of Bengal should form around April 21.

“This year, however, it was seen in satellite pictures and low-level wind charts during the last two to three days indicating that the monsoon onset over Kerala is likely to be early by about a week.”

On occasions in the past, the raining cloud band and the westerly winds associated with it has caused the genesis of a depression or a cyclonic storm in the Bay of Bengal, just to its north.

In addition, the surface temperature of Bay of Bengal is warmer than normal by about one degree Celsius this year.

Dry air, heat waves

“We may expect the formation of a cyclonic storm in the Bay during April 15 to 20. But soon after that the raining clouds are likely to shift to the western Pacific ocean."

During the period from May 1 to 10, India is likely to face largely dry conditions with decreased rainfall and occurrence of heat waves.

From around May 10, a band of raining clouds is likely to form over the South Arabian Sea, which will increase in area covered and intensity to bring about the monsoon onset over Kerala around May 25, accompanied by strong low level winds and heavy and persistent rainfall.

This description is based on the climatology (average) of the monsoon onset process that takes place over the Indian Ccean during the 40-day period after the pre-moonsoon rainfall peak, Joseph said.

Published on April 13, 2017
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