The South-West monsoon is expected to set in at least a week ahead of schedule this year, according to renowned scientist and monsoon researcher PV Joseph.

But the early onset does not have any relevance to its ultimate performance during the rest of the four-month season that ends in September.

India Met Department (IMD) often reaches out to the Kochi-based Joseph for making its own long-range monsoon forecast. He is a former director of its Meteorological Training School in Pune.

Pre-monsoon peak Joseph based his outlook on what is called the pre-monsoon rain peak, a chain of events starting from the warming of the south Bay of Bengal and leading up to the break-out of thundershowers over Kerala.

Situated along the south-west coast of the country, Kerala is considered as the gateway for the monsoon, the annual rain season which is crucial for the country’s farm economy.

Joseph said in an e-mailed interview to BusinessLine that the end of the first week of April 2015, central Bay of Bengal had ‘begun warming up fast’ as seen from measurements by satellites.

By April 8 (Wednesday last), sea surface temperatures (SST) there had reached 30-31 degree Celsius.

Elevated warmth of the sea accelerates the process of evaporation and is the driving force behind the formation of thunderclouds.

Early this year Rain-bearing clouds began forming to the south of this region of high SST – south Bay of Bengal, to be precise – as well as over Kerala from Wednesday.

This made up for the pre-monsoon rain peak of 2015. This is a phenomenon discovered by Joseph and co-researchers in 1988, and considered a major milestone event ahead of onset of the monsoon over Kerala

. “The pre-monsoon rain peak has formed this year about 10 days earlier than normal, an indication of earlier than normal monsoon onset over Kerala,” Joseph told BusinessLine .

He pointed to the fact that Kerala has been receiving scattered thunder rains from Wednesday and which continues till date.

“Based on the pre-monsoon peak, the monsoon is likely to set in over Kerala a week earlier than normal, by 24th May 2015 (plus or minus 3 days),” Joseph added.

Thunderstorm season The long term average date of monsoon onset over Kerala is June 1.

Joseph is currently Professor Emeritus at the Department of Atmospheric science, Cochin University of Science and Technology, Cochin.

In response to a question, he said that April and May are the months for severe thunderstorms in north India and in particular the north-eastern regions (Kal Baisakhi). It is usual for these events to show up to the accompaniment of hailstorms and occasionally tornadoes.

“What is occurring currently in North and East India and Bangladesh now is normal for this season.”

Joseph is credited with doing original research for five decades in tropical meteorology (monsoons, cyclones and thunderstorms), climate change and ocean-atmosphere interaction.

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