Finally, the southwest monsoon is at Kerala’s doorstep, delayed by over one week compared to the normal onset date of June 1. Though the delay has raised some anxious moments across the country, the data with the India Meteorological Department (IMD) reveal that monsoon onset is not linked to the performance of the monsoon in the four-month season in the country, especially in Kerala, which acts as the gateway for monsoon to the Indian subcontinent.
In the last 121 years of the recorded history of the southwest monsoon, the earliest onset was in 1918 (May 11) and the most delayed onset was in 1972 (June 18). But in both years, the southwest monsoon was deficient in the State. Interestingly, 1918 witnessed the lowest ever rainfall in Kerala with only 110 cm during the season against the average of around 201 cm.
72% deficient
Similarly, as per the latest weather bulletin of the IMD, the monsoon is expected to hit the Kerala coast before June 9. As of June 7, the monsoon rainfall is 72% deficient in Kerala and the current synoptic conditions hint at a weak onset over Kerala till the first half of June. Thereafter, it is likely to gain momentum.
The IMD data say the June rainfall was deficient for around 27 years in the past 121 years. Of these 27 years, the monsoon was deficient in Kerala only seven times. So, the June rainfall is not a deciding factor in the performance of monsoon rainfall, says a senior IMD scientist.
In fact, the three global factors decide the performance of the monsoon — El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and Madden Julian Oscillation (MJO).
The former two are neutral, while MJO is a rotating cloud mass around the globe with a frequency of 30 to 60 days. It has eight phases. It reaches phase 2 when it is in the Arabian Sea (AS) and phase 3 when it is in the Bay of Bengal. Other phases are in different regions. At present, the MJO is likely to support convective activity, along with cyclogenesis over the Arabian Sea and Bay of Bengal. Further, by the end of next week, the IOD is likely to be positive enhancing the precipitation along the west coast, including Kerala, says the scientist.
