Late Monsoon | National

Monsoon onset over Kerala delayed

Last year too, the monsoon had been forecast to arrive by May 31 but it landed on June 3. File photo

Last year too, the monsoon had been forecast to arrive by May 31 but it landed on June 3. File photo | Photo Credit: PTI

Monsoon has missed its May 27 date with Kerala, with the India Meteorological Department (IMD) saying that it will likely to take “2-3 days more” for the onset.

On May 13, the IMD announced that monsoon was to arrive on May 27, four days ahead of its normal date of June 1 and making it the earliest monsoon onset in 13 years over Kerala.

Friday’s forecast said the monsoon system had further advanced into parts of the South Arabian Sea, Maldives and parts of Lakshadweep as well as the Comorin area.

Westerly winds had strengthened in the lower levels over the south Arabian Sea and there was an increase in cloudiness over the Kerala coast and adjoining southeast Arabian Sea, the IMD update stated.

Three key criteria

For the IMD to declare the onset over Kerala, three key criteria must be met: One, the rain-bearing westerlies have to be at a minimum depth and speed; two, at least 60% of the available 14 stations in Kerala and coastal Karnataka, namely Minicoy, Amini, Thiruvananthapuram, Punalur, Kollam, Allapuzha, Kottayam, Kochi, Thrissur, Kozhikode, Thalassery, Kannur, Kudulu and Mangalore, must reporting rainfall of 2.5 mm or more for two consecutive days after May 10; and, finally, a certain degree of clouding, indicated by a parameter called outgoing longwave radiation being below 200 W/square metre.

IMD Director General M. Mohapatra told The Hindu that all criteria had been met except the stations criteria. “As of today, 50% of the stations have received required rain. It is quite possible that this may be met tomorrow of day after.”

Other agencies suggest that while the monsoon’s advent will likely be a weak onset, meaning that the monsoon may be stalled over the Kerala and Karnataka coast for the first few days of June instead of travelling northwards onto Maharashtra.

MJO phenomenon

A phenomenon called the Madden-Julian Oscillation (MJO) — a tropical wave that travels around the equator every 30-40 days — influences precipitation patterns in India as well. The current MJO signal (active phase) that lies over the Indian Ocean could trigger the onset of monsoon over Kerala by May 27. However, the MJO could enter an “inactive phase” by May-end and favour a slow progress of monsoon. “Therefore, amidst the prevailing weak La Niña conditions, there is a chance that that the onset and subsequent progress of monsoon over Kerala and Karnataka can be delayed to the first week of June,” according to an analysis by The Weather Company, a firm that tracks monsoon patterns.

Last year too, the monsoon had been forecast to arrive by May 31 but officially it landed on June 3 after which the progress was slow. The IMD uses a specialised weather model to forecast the monsoon onset over Kerala and the forecast date has a built-in four day margin of error. Except for 2015, the monsoon has arrived within the four-day window of the date forecast by the IMD from 2005-2021, the agency said in a press statement.

It has forecast the June-September monsoon to be normal with rainfall likely to be 99% of the historical normal.

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Printable version | May 28, 2022 8:14:55 am |