By TWC India Edit Team
Thursday, May 26: After what has been a scorching summer riddled with heatwaves and above-average temperatures, it is finally time for Southern India to welcome the wettest period of the year: the southwest monsoon season.
Due to the movement and direction of these monsoon winds, the first monsoon showers mark their arrival over the Indian mainland by drenching the southernmost parts of Kerala. Over the past several decades, this onset of monsoon in ‘God’s Own Country’ has occurred on or around June 1.This year, however, the opening monsoon rains may land in Kerala up to five days earlier than normal — on May 27, 2022 (+/- 4 days).
“The monsoon onset conditions in Kerala are currently favourable. The actual onset is likely to occur on May 27, with a model error of four days. The monsoon has already progressed up to the Sri Lankan region,” an official from the India Meteorological Department’s (IMD) regional met office in Thiruvananthapuram told weather.com.
Further, the daily forecast issued by the IMD has indicated that as of Thursday morning, the conditions remain favourable for the further advancement of monsoon over some parts of Southwest Arabian Sea, some more parts of Southeast Arabian Sea, Maldives and Comorin area, south and east-central Bay of Bengal and some parts of northeast Bay of Bengal during next 24 hour.
The onset of monsoon has always been tricky, and over the last 50 years, the date of onset in Kerala has ranged from May 19 (in 1990) to June 18 (in 1972). This variance is in large attributed to the state of the ENSO — El Niño–Southern Oscillation — in the preceding winter.
The Madden-Julian Oscillation (MJO) — a tropical wave that travels around the equator every 30-40 days — also modulates the precipitation patterns in India. The current MJO signal (active phase) lies over the Indian Ocean and will likely trigger the onset of monsoon over Kerala by May 27.
However, the MJO may enter an inactive phase by the end of May. This suppression may subsequently favour a slow progress of monsoon, even though the background state weakly favours an earlier start. Therefore, amidst the prevailing weak La Niña conditions, there is a chance that the onset and subsequent progress of monsoon over Kerala and Karnataka can be delayed until the first week of June.The IMD officially declares the monsoon onset when around 60% of the available weather stations in the state record rainfall of 2.5 mm or more for two consecutive days after May 10.
If these conditions are met, and if the technical criteria for wind field and outgoing longwave radiation are fulfilled, then the onset over Kerala is usually declared on the second day.In 2020, the IMD revised the normal dates of onset and withdrawal of monsoon across India, based on the average dates of southwest monsoon’s arrival between 1961 to 2019. However, for Kerala, the new normal remains the same as the old, June 1.
Meanwhile, the IMD’s long-range forecast has indicated that the monsoon’s performance this year is likely to be normal. Quantitatively, the seasonal precipitation may amount to 87 cm — around 99% of India’s long-period average for monsoons.
As for the ongoing pre-monsoon season, it was certainly much wetter than normal for Kerala. Between March 1 and May 25, the state has collectively recorded 615.1 mm precipitation, which is a 108% ‘large excess’ compared to its long-term average for this period (295.4 mm). Even at present, widespread rains continue to drench Kerala, in what could be the final pre-monsoon rain spell of the year.